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Soalan mengenai dicumarol

Soalan mengenai dicumarol


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Saya tahu bahawa dicumarol ditemui dalam semanggi manis berkulat kerana ia menyebabkan pendarahan pada lembu, tetapi jika seseorang mengalami gangguan tromboemboli yang menyebabkan trombosis yang tidak terkawal, adakah baik untuk makan semanggi manis berkulat (sekiranya tiada sebarang cara hidup moden) terutamanya yang ia mengandungi mikroorganisma lain?


Kaji Soalan dan Jawapan Mudah tentang Darah

Darah adalah alat pengangkutan bahan ke seluruh badan. Darah mengedarkan nutrien, oksigen, hormon, antibodi dan sel khusus dalam pertahanan kepada tisu dan mengumpul sisa seperti sisa nitrogen dan karbon dioksida daripadanya.

Komponen Darah

Lagi Soal Jawab Bersaiz Gigitan Di Bawah

2. Apakah unsur yang membentuk darah?

Darah terdiri daripada cecair dan bahagian selular. Bahagian cecair dipanggil plasma dan mengandungi beberapa bahan, termasuk protein, lipid, karbohidrat dan garam mineral. Komponen selular darah juga dikenali sebagai sel darah dan ia termasuk eritrosit (sel darah merah), leukosit dan platelet.

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Hematopoiesis, Sumsum Tulang dan Sel Stem

3. Apakah hematopoiesis?

Hematopoiesis ialah pembentukan sel darah dan unsur-unsur lain yang membentuk darah.

4. Di manakah hematopoiesis berlaku?

Hematopoiesis berlaku dalam sumsum tulang (terutamanya dalam tulang rata), di mana eritrosit, leukosit dan platelet dibuat dan dalam tisu limfoid, yang bertanggungjawab untuk kematangan leukosit dan yang terdapat dalam timus, limpa dan nodus limfa.

5. Di dalam tulang manakah sumsum tulang boleh ditemui terutamanya? Adakah sumsum tulang diperbuat daripada tisu tulang?

Sumsum tulang terutamanya boleh ditemui di rongga dalaman tulang rata, seperti vertebra, rusuk, tulang belikat, sternum dan pinggul.

Sumsum tulang tidak diperbuat daripada tisu tulang, walaupun ia adalah tisu penghubung seperti tisu tulang.

6. Apakah sel stem darah?

Sel stem ialah sel yang tidak dibezakan yang dapat membezakan kepada jenis sel khusus yang lain.

Sel stem sumsum tulang menghasilkan sel darah yang berbeza. Bergantung kepada rangsangan daripada faktor pertumbuhan tertentu, sel stem bertukar menjadi sel darah merah, leukosit dan megakaryocytes (sel yang membentuk platelet). Penyelidikan menunjukkan bahawa sel stem sumsum tulang juga boleh membezakan kepada sel otot, saraf dan hepatik.

Sel Darah Merah dan Hemoglobin

7. Apakah nama lain untuk eritrosit? Apakah fungsi sel-sel ini?

Eritrosit juga dikenali sebagai sel darah merah (RBC) atau sel darah merah. Sel darah merah bertanggungjawab untuk mengangkut oksigen dari paru-paru ke tisu.

8. Apakah nama molekul dalam sel darah merah yang mengangkut oksigen?

Pigmen pernafasan sel darah merah dipanggil hemoglobin.

9. Apakah komposisi molekul hemoglobin? Adakah fungsi hemoglobin sebagai protein bergantung kepada struktur tertier atau kuaternernya?

Hemoglobin ialah molekul yang diperbuat daripada empat rantai polipeptida, setiap satu terikat kepada kumpulan molekul yang mengandungi besi yang dipanggil kumpulan heme. Oleh itu, molekul mengandungi empat rantai polipeptida dan empat kumpulan heme.

Sebagai protein yang terdiri daripada rantai polipeptida, kefungsian hemoglobin bergantung kepada integriti struktur kuaternarinya.

10. Secara purata, berapakah jangka hayat sel darah merah? Di manakah mereka dimusnahkan? Ke manakah perginya kumpulan heme selepas pemusnahan molekul hemoglobin?

Secara purata, sel darah merah hidup sekitar 120 hari. Limpa adalah organ utama di mana sel darah merah lama dimusnahkan.

Semasa pemusnahan sel darah merah, kumpulan heme bertukar menjadi bilirubin dan bahan ini kemudiannya ditangkap oleh hati dan kemudiannya dikumuhkan ke usus sebagai sebahagian daripada hempedu.

11. Apakah fungsi limpa? Mengapakah orang masih boleh hidup selepas splenektomi total (pembedahan pembuangan limpa)?

Limpa mempunyai banyak fungsi: ia mengambil bahagian dalam pemusnahan sel darah merah lama di dalamnya leukosit khusus matang ia membantu menjana semula tisu hematopoietik sumsum tulang apabila perlu dan ia boleh bertindak sebagai organ seperti span untuk mengekalkan atau melepaskan darah ke dalam peredaran. .

Tidak mustahil untuk hidup selepas splenektomi total kerana tiada satu pun fungsi limpa adalah penting dan eksklusif untuk  organ ini.

Anemia Diterangkan

12. Apakah anemia? Apakah empat jenis utama anemia?

Anemia adalah kepekatan hemoglobin yang rendah dalam darah.

Empat jenis anemia utama ialah anemia kekurangan nutrien, anemia yang disebabkan oleh kehilangan darah, anemia hemolitik dan anemia aplastik.

Anemia kekurangan nutrien disebabkan oleh kekurangan pemakanan dalam nutrien asas yang diperlukan untuk penghasilan atau fungsi sel darah merah, seperti zat besi (anemia kekurangan zat besi), vitamin B12 dan asid folik.

Anemia yang disebabkan oleh kehilangan darah berlaku dalam keadaan hemoragik atau dalam penyakit seperti ulser peptik dan penyakit cacing tambang.

Anemia hemolitik disebabkan oleh pemusnahan sel darah merah yang berlebihan, contohnya, dalam penyakit seperti malaria atau dalam keadaan hipervolemik (air berlebihan dalam darah menyebabkan lisis sel darah merah).

Anemia aplastik berlaku daripada kekurangan dalam hematopoiesis dan berlaku apabila sumsum tulang dicederakan oleh kanser daripada tisu lain (metastasis), oleh penyakit autoimun, oleh mabuk dadah (seperti ubat sulfa dan antikonvulsan) atau oleh bahan kimia (seperti benzena, racun serangga, cat. , racun herba dan pelarut secara umum). Sesetengah penyakit genetik juga menjejaskan sumsum tulang, menyebabkan anemia aplastik.

Sel darah putih

13. Apakah perbezaan antara sel darah putih dan sel darah merah? Apakah leukosit?

Sel darah merah dipanggil eritrosit dan sel darah putih dipanggil leukosit.

Leukosit adalah sel khusus dalam pertahanan badan terhadap agen asing dan merupakan sebahagian daripada sistem imun.

14. Apakah jenis leukosit yang berbeza dan bagaimana ia dikelaskan kepada granulosit dan agranulosit?

Jenis leukosit ialah limfosit, monosit, neutrofil, eosinofil dan basofil. Granulosit ialah mereka yang mempunyai sitoplasma yang mengandungi butiran (apabila dilihat di bawah mikroskop elektron): neutrofil, eosinofil dan basofil ialah granulosit. Agranulosit adalah leukosit lain: limfosit dan monosit.

15. Apakah fungsi generik leukosit? Apakah leukositosis dan leukopenia?

Fungsi generik leukosit adalah untuk mengambil bahagian dalam pertahanan badan terhadap agen asing yang menembusinya atau dihasilkan di dalam badan.

Leukositosis dan leukopenia adalah keadaan klinikal di mana sampel darah mengandungi kiraan leukosit yang tidak normal. Apabila jumlah leukosit dalam sampel darah melebihi paras normal bagi individu, ia dipanggil leukositosis. Apabila kiraan leukosit lebih rendah daripada paras normal yang dijangkakan, ia dipanggil leukopenia. Pendaraban sel pertahanan ini, leukositosis, biasanya berlaku apabila badan mengalami jangkitan atau dalam kanser sel-sel ini. Kiraan rendah sel pertahanan ini, atau leukopenia, berlaku apabila beberapa penyakit, seperti AIDS, menyerang sel atau apabila ubat imunosupresif digunakan.

Secara umum, badan menggunakan leukositosis sebagai tindak balas pertahanan apabila ia menghadapi agen berjangkit atau patogen. Oleh itu, keadaan klinikal leukositosis adalah tanda jangkitan. Leukopenia berlaku apabila terdapat kekurangan dalam pengeluaran (contohnya, dalam penyakit sumsum tulang) atau pemusnahan leukosit yang berlebihan (contohnya, dalam kes jangkitan HIV).

Platelet dan Hemostasis

16. Apakah mekanisme untuk mengandungi pendarahan yang dipanggil?

Mekanisme fisiologi untuk mengandungi pendarahan (salah satunya ialah pembekuan darah) secara umum dipanggil hemostasis, atau proses hemostatik.

17. Bagaimanakah platelet terbentuk? Apakah fungsi platelet? Apakah akibat klinikal daripada keadaan yang dikenali sebagai trombositopenia?

Platelet, juga dikenali sebagai trombosit, adalah serpihan sel sumsum tulang besar yang dipanggil megakaryocytes. Melalui sifat pengagregatan dan pelekat mereka, mereka terlibat secara langsung dalam pembekuan darah serta membebaskan bahan yang mengaktifkan proses hemostatik lain.

Trombositopenia adalah keadaan klinikal di mana kiraan platelet darah seseorang individu adalah lebih rendah daripada biasa. Dalam keadaan ini, orang itu menjadi terdedah kepada pendarahan.

Lata Pembekuan

18. Bagaimanakah badan mengetahui bahawa proses pembekuan mesti bermula?

Apabila luka tisu mengandungi kecederaan pada saluran darah, platelet dan sel endothelial dinding pembuluh yang rosak melepaskan bahan (faktor platelet dan faktor tisu, masing-masing) yang mencetuskan proses pembekuan.

19. Bagaimanakah proses pembekuan darah (pembekuan) boleh diterangkan?

Pembekuan darah merangkumi urutan tindak balas kimia yang produknya adalah enzim yang memangkinkan tindak balas berikutnya (sebab itu tindak balas pembekuan dipanggil tindak balas lata). Dalam plasma, tromboplastinogen berubah menjadi tromboplastin, tindak balas yang dicetuskan oleh tisu dan faktor platelet yang dikeluarkan selepas kecederaan pada saluran darah. Bersama dengan ion kalsium, tromboplastin kemudian memangkinkan perubahan protrombin kepada trombin. Thrombin kemudian memangkinkan tindak balas yang menghasilkan fibrin daripada fibrinogen. Fibrin, sebagai bahan tidak larut, membentuk rangkaian yang memerangkap sel darah merah dan platelet, dengan itu membentuk bekuan darah dan mengandungi pendarahan.

20. Apakah faktor pembekuan?

Faktor pembekuan ialah bahan (enzim, koenzim, reagen) yang diperlukan untuk proses pembekuan berlaku. Sebagai tambahan kepada faktor pencetus dan reagen yang telah diterangkan (faktor tisu dan platelet, thromplastinogen, prothrombin, fibrinogen, ion kalsium), bahan lain mengambil bahagian dalam proses pembekuan darah sebagai faktor pembekuan. Salah satunya ialah faktor VIII, kekurangannya menyebabkan hemofilia A, dan satu lagi ialah faktor IX, kekurangannya menyebabkan hemofilia B.

21. Dalam organ manakah kebanyakan faktor pembekuan dihasilkan? Apakah peranan vitamin K dalam pembekuan darah?

Kebanyakan faktor pembekuan dihasilkan di hati.

Vitamin K mengambil bahagian dalam pengaktifan beberapa faktor pembekuan dan penting untuk pembekuan darah berfungsi dengan baik.

Hemofilia Diterangkan

22. Apakah faktor VIII? Apakah penyakit genetik di mana faktor ini tidak hadir?

Faktor VIII mempunyai fungsi mengaktifkan faktor X, yang seterusnya diperlukan untuk transformasi protrombin menjadi trombin semasa lata pembekuan. Hemofilia A ialah penyakit genetik berkaitan X di mana individu tidak menghasilkan faktor VIII dan akibatnya lebih terdedah kepada pendarahan yang teruk.

23. Bagaimanakah hemofilia dirawat? Mengapa hemofilia jarang berlaku pada wanita?

Hemofilia dirawat secara perubatan dengan pemberian faktor VIII, dalam kes hemofilia A, atau faktor IX, dalam kes hemofilia B, melalui darah atau pemindahan plasma beku segar.

Kedua-dua hemofilia A atau B adalah penyakit resesif berkaitan X. Untuk seorang gadis menjadi hemofilik, kedua-dua kromosom Xnya perlu terjejas manakala kanak-kanak lelaki, yang hanya mempunyai satu kromosom X, lebih mudah terjejas. Seorang gadis dengan hanya satu kromosom terjejas tidak menunjukkan penyakit ini, kerana gen normal kromosom X yang tidak terjejas menghasilkan faktor pembekuan.

24. Apakah perkaitan epidemiologi antara hemofilia dan jangkitan HIV?

Oleh kerana pesakit hemofilik memerlukan pemindahan faktor pembekuan yang kerap (VIII atau IX), mereka lebih mudah terdedah kepada pencemaran oleh agen berjangkit yang terdapat dalam darah dari mana unsur transfusi datang. Pada masa lalu, bank darah biasanya tidak melakukan ujian pengesanan HIV dan ramai pesakit hemofilik telah dijangkiti virus tersebut.

Antikoagulasi dan Fibrinolisis

25. Apakah antikoagulan? Apakah aplikasi praktikal antikoagulan, seperti heparin, dalam Perubatan?

Antikoagulan adalah bahan yang menyekat tindak balas pembekuan dan oleh itu menghentikan proses pembekuan. Biasanya, antikoagulan beredar dalam plasma, kerana dalam keadaan normal darah mesti dikekalkan cecair.

Dalam Perubatan, antikoagulan seperti heparin digunakan dalam pembedahan di mana kecederaan tisu yang disebabkan oleh tindakan pembedahan boleh mencetuskan pembekuan darah sistemik yang tidak diingini. Ia juga digunakan untuk mengelakkan pembentukan trombi di dalam saluran darah pesakit berisiko meningkatkan risiko trombosis.

26. Apakah dicoumarol? Apakah peranan bahan ini dalam proses pembekuan dan apakah beberapa contoh ketoksikannya?

Dicoumarol adalah ubat antikoagulan. Oleh kerana struktur molekulnya, dicoumarol bersaing dengan vitamin K untuk mengikat substrat, dengan itu menyekat pembentukan faktor pembekuan dan mengganggu pengeluaran prothrombin. Dicoumarol terdapat dalam beberapa sayur-sayuran yang reput dan boleh menyebabkan pendarahan dalaman yang teruk apabila sayur-sayuran tersebut termakan secara tidak sengaja. Antikoagulan kumarin tidak boleh diberikan semasa kehamilan kerana ia melepasi halangan plasenta dan boleh menyebabkan pendarahan janin.

27. Streptokinase ialah bahan yang digunakan dalam rawatan infarksi miokardium akut. Apakah fungsi bahan ini?

Bahan yang dikenali sebagai fibrinolitik, seperti streptokinase dan urokinase, boleh memusnahkan trombi (gumpalan yang terbentuk di dalam saluran darah, kapilari atau di dalam bilik jantung) dan digunakan dalam rawatan halangan arteri koronari atau saluran darah lain.

Streptokinase memusnahkan rangkaian fibrin dan sebagai hasilnya melarutkan bekuan trombotik. Namanya berasal dari bakteria yang menghasilkannya, streptokokus.


Kandungan Esei:

  1. Esei tentang Pengenalan kepada Pembekuan Darah
  2. Esei tentang Kaedah Menentukan Pembekuan Darah
  3. Esei Kepentingan Pembekuan Darah
  4. Esei Mekanisme Pembekuan Darah
  5. Esei Faktor-Faktor Yang Mempengaruhi Pembekuan Darah
  6. Karangan Mengenai Penyakit Yang Berlaku Akibat Pembekuan Darah
  7. Esei tentang Perencatan Semulajadi Pembekuan Darah
  8. Esei Faktor-Faktor Mencegah dan Mempercepatkan Pembekuan Darah

Esei # 1. Pengenalan kepada Pembekuan Darah:

Apabila darah ditumpahkan, ia kehilangan kecairannya dalam beberapa minit dan menjadi jeli separuh pepejal. Fenomena ini dipanggil pembekuan darah atau pembekuan. Apabila disimpan lebih lanjut, bekuan itu ditarik balik kepada jumlah yang lebih kecil dan menekan keluar cecair berwarna straw yang jelas, dipanggil serum. Serum tidak akan beku lagi.

Apabila proses pembekuan darah dikaji di bawah ultra-mikroskop, ia dilihat bahawa, butiran kecil muncul pada mulanya, selalunya berhampiran rumpun platelet yang hancur. Butiran ini bercantum untuk membentuk jarum, yang sekali lagi bersatu antara satu sama lain untuk membentuk benang panjang di seluruh sebahagian besar darah. Benang-benang ini bersilang antara satu sama lain dan membentuk semacam rangkaian, ke dalam jaringan yang mana sel merah dan putih menjadi terjerat. Gumpalan secara beransur-ansur menarik balik dan serum terpisah.

Perlu diingatkan bahawa pembekuan darah adalah milik plasma sahaja. Sel merah dan putih tidak mengambil bahagian di dalamnya. Mereka hanya terperangkap dalam jaringan bekuan dan dengan itu dikeluarkan. Ia disebabkan oleh fakta ini bahawa bekuan mempunyai warna merah, dan serum adalah cecair bukan selular yang jelas. Platlet darah mengambil bahagian dalam proses itu.

Masa Pembekuan Normal:

Diukur mengikut kaedah Lee and White adalah 6 hingga 17 minit dalam tiub kaca dan 19 hingga 60 minit dalam tiub silikon.

Esei # 2. Kaedah Menentukan Pembekuan Darah:

i. Kaedah Tiub Kaca Kapilari:

Kaedah ini biasanya digunakan sebagai prosedur sisi katil. Jari dicucuk dan darah dibuat untuk mengalir ke dalam tiub kaca kapilari sepanjang kira-kira 15 cm (6 inci). Sedikit kecil tiub kaca dipecahkan dengan teliti setiap lima belas saat sehingga benang halus darah beku muncul semasa tiub itu dipecahkan. Tempoh antara penampilan darah di jari dan pembentukan benang ini diambil sebagai masa pembekuan darah. Masa purata, dengan kaedah ini, ialah 3-4 minit.

ii. Coagulometer Wright’s:

Prinsipnya sama seperti di atas. Darah dibenarkan mengalir ke dalam sedozen tiub kapilari yang sama berkaliber. Tiub dimeteraikan pada kedua-dua belah dan diletakkan di dalam tab mandi air pada suhu 37°C. Selepas 4 minit, tiub pertama (tiub yang mula-mula diisi dengan darah) dikeluarkan dari tab mandi air, hujungnya pecah dan darah di dalamnya dikeluarkan ke dalam air. Prosedur yang sama diulang dengan semua tiub lain pada selang 30 saat. Apabila darah yang dikeluarkan dari tiub tertentu mempunyai bentuk bekuan seperti cacing, titik akhir dicapai.

iii. Kaedah Lee dan White:

1 ml darah diambil dari vena dengan picagari kering dan diletakkan dalam dua tabung uji bersih, berdiameter 8 mm. Tiub ditutup dengan gabus getah. Pada 5 minit selepas pengeluaran darah mengikut cara yang diterangkan, tiub pertama dicondongkan perlahan-lahan 45 darjah pada selang satu minit sehingga ia boleh diterbalikkan 180 darjah tanpa darah mengalir.

Masa ini direkodkan dan prosedur yang sama diulang dengan tiub kedua. Memandangkan pengendalian memihak kepada pembekuan, masa untuk tiub kedua diambil sebagai masa pembekuan darah sebenar kerana ia dicondongkan kurang daripada tiub pertama.

Purata biasa ialah 3.25 minit, julatnya ialah 2-5 minit. Ia biasanya ditentukan oleh kaedah Duke’s. Lobul telinga ditebuk dan masa dicatatkan. Darah yang mengalir keluar dimop dengan sekeping kertas penapis setiap setengah minit sehingga pendarahan berhenti. Ini menunjukkan titik akhir.

Masa Prothrombin (Pantas):

Anggaran masa protrombin biasanya 11 hingga 16 saat. Apabila ekstrak tisu (tromboplastin) dan kalsium klorida dicampur (ditambah) dalam jumlah optimum kepada darah kandungan fibrinogen normal, satu-satunya faktor yang mempunyai kepekatan protrombin yang tidak mencukupi, boleh mengubah masa pembekuan.

Jika protrombin berkurangan, masa pembekuan darah meningkat. Ujian ini adalah ujian kuantitatif untuk protrombin dalam darah berdasarkan masa pembekuan darah plasma darah teroksidasi dengan kehadiran ekstrak tisu (tromboplastin) dan kalsium klorida.

Di setiap makmal, lengkung kepekatan protrombin dalam darah kepada masa protrombin biasanya dibuat untuk penilaian masa protrombin. Satu-satunya langkah berjaga-jaga ialah darah yang dikeluarkan daripada pesakit segera teroksidasi supaya tiada protrombin boleh ditukar menjadi trombin.

Dalam tabung uji 0.2 ml tromboplastin komersial yang mengandungi kalsium disimpan pada suhu 37°C. Selepas 30 saat, 0.1 ml plasma ditambah dengan cepat daripada pipet, dan jam randik dimulakan serentak. Tiub itu disimpan di dalam tab mandi air dan digoncang sentiasa tetapi perlahan-lahan selama 10 saat. Kemudian dalam pencahayaan langsung yang terang, tiub dicondongkan secara berterusan dari kedudukan menegak ke hampir mendatar sekali sesaat sehingga gel muncul.

Ini adalah titik akhir. Nilai 11 hingga 16 saat adalah memuaskan, tetapi ujian hendaklah sentiasa dilakukan dalam pendua.

Esei # 3. Kepentingan Pembekuan Darah:

Fenomena pembekuan adalah kepentingan fisiologi yang sangat besar. Tujuannya adalah untuk menghentikan hae­morrhage selanjutnya. Apabila pendarahan berlaku, darah yang ditumpahkan membeku dan saluran pendarahan tersumbat oleh bekuan itu.

Penarikan semula bekuan itu memampatkan lagi saluran yang pecah dan dengan cara ini pendarahan dihentikan.

Esei # 4. Mekanisme Pembekuan Darah:

Seawal 1904 Morawitz menerangkan fakta asas tentang mekanisme pembekuan darah dengan cara berikut. Apabila darah ditumpahkan, platelet (dengan bersentuhan dengan permukaan meja basah-air yang kasar), hancur dan membebaskan tromboplastin.

Jumlah tromboplastin tertentu juga diperoleh daripada tisu yang rosak di kawasan yang cedera. Tromboplastin menukar protrombin kepada trombin dengan bantuan ion kalsium dan trombin berinteraksi -dengan fibrinogen membentuk fibrin.

Ini adalah bekuan. Teori ini boleh diringkaskan dalam langkah-langkah berikut:

Protrombin + Kalsium ion + Fibrinogen → Nil

Selepas pertumpahan darah:

1. Thromboplastin + Prothrombin + Kalsium ion → Thrombin

2. Thrombin + Fibrinogen → Fibrin (Bekuan).

Sejak tahun 1940, kerja penyelidikan telah menunjukkan bahawa mekanisme pembekuan adalah proses yang kompleks. Pada tahun 1954 sebuah Jawatankuasa Inter­national telah ditubuhkan. Jawatankuasa itu mencadangkan sistem tatanama antarabangsa dari semasa ke semasa dengan kemunculan faktor baru.

Esei # 5. Faktor-faktor yang Mempengaruhi Pembekuan Darah:

Faktor I atau Fibrinogen:

Ia bersifat globulin tetapi mempunyai molekul yang jauh lebih besar daripada serum globulin. Berat molekul adalah kira-kira 330,000. Ia terkoagulasi pada kira-kira 56°C dan dimendakkan oleh ketepuan satu perlima dengan ammonium sulfat dan tepu dengan NaCl. Ia dibezakan daripada protein plasma lain dengan sifat pembekuannya, di mana fibrinogen ditukar menjadi fibrin.

Faktor II atau Protrombin:

Ia bersifat protein dan terdapat dalam plasma normal. Ia mempunyai berat molekul kira-kira 62,700. Ia sangat labil dalam larutan akueus dan dinyahaktifkan oleh asid pada pH 4.8, oleh alkali pada pH 10.0 dan oleh haba pada 60°C tetapi stabil selama-lamanya apabila dikeringkan daripada keadaan beku. Dalam plasma oksalat, dua bentuk protrombin ditemui ‘A’ dan ‘B’.

Bentuk A’ dimusnahkan oleh oksigen dan labil haba. Bentuk ‘B’ boleh ditanggalkan oleh aluminium hidroksida. Dalam plasma biasa kedua-dua bentuk kekal bersatu sebagai sebatian kalsium. Apabila oksalat ditambah, kalsium dikeluarkan dan kedua-dua komponen menjadi berasingan.

Ia boleh diasingkan seperti berikut:

Jika pH plasma diselaraskan pada 5.3, kedua-dua protrombin dan globulin dimendakan. Prothrombin dibubarkan dengan merawat mendakan dengan kalsium bikarbonat cair. Selepas penapisan pH turasan sekali lagi dilaraskan kepada 5.3 apabila protrombin berpisah. Dalam bentuk ini ia adalah serbuk putih, tidak larut dalam air dan kekal digabungkan dengan protein. 100 ml plasma mengandungi 40 mgm bahan ini.

Aktiviti prothrombin darah diukur dengan masa pembekuan plasma oksalat yang dikalsifikasi semula, yang mana emulsi tisu telah ditambah. Dalam subjek manusia, purata ‘masa protrombin’ ialah 12 saat. Masa protrombin akan lebih lama dalam kekurangan faktor V atau faktor VII atau faktor Stuart. Prothrombin dihasilkan di hati. Vitamin K adalah penting untuk pembentukan prothrombin. Semasa pembekuan, prothrombin ditukar menjadi trombin.

Faktor III atau Thromboplastin:

Ia diperoleh daripada dua sumber:

1. Intrinsik dalam Plasma:

Tromboplastin intrinsik terbentuk dalam plasma akibat interaksi antara faktor plasma yang berbeza, contohnya, faktor Hageman atau faktor XII, PTA atau faktor XI, faktor Krismas atau faktor IX, globulin antihaemofilik atau faktor VIII, ion kalsium, faktor V dan faktor X.

Prothrombin ditukar kepada trombin dengan bantuan tromboplastin intrinsik dengan kehadiran ion kalsium. Perlu diingatkan bahawa darah yang mengalir secara normal melalui sistem peredaran darah tidak akan membeku. Tetapi jika permukaan saluran darah menjadi kasar atas sebab apa pun, darah akan membeku walaupun tanpa penambahan ekstrak tisu (tromboplastin ekstrinsik).

2. Ekstrinsik atau Tromboplastin Tisu:

Ia terbentuk daripada tisu yang berbeza, cth., ekstrak otak, paru-paru, dsb., akibat kecederaan. Sejak sekian lama diketahui bahawa prothrombin telah ditukar kepada trombin dengan bantuan ion kal­cium dan tromboplastin yang dibebaskan daripada tisu yang rosak. Tetapi baru-baru ini didapati bahawa pelbagai faktor plasma, contohnya, faktor VII atau proconvertin, diperlukan untuk penukaran tersebut dan proses itu dipanggil pembentukan tromboplastin ekstrinsik.

Faktor IV atau Kalsium:

Kalsium ionik sangat membantu dalam pembekuan darah dengan bertindak sebagai kofaktor dalam proses pembekuan darah. Ia adalah penting untuk pembentukan kedua-dua tromboplastin intrinsik dan ekstrinsik dan juga dalam penukaran protrombin kepada trombin.

Faktor V atau Labile Factor Accelerator Globulin atau Proaccelerin:

Faktor ini diperlukan untuk penukaran lengkap protrombin kepada trombin oleh tromboplastin ekstrinsik atau intrinsik. Ia adalah protein, tahan haba dan diaktifkan dalam masa setengah jam pada 56°C atau dengan meningkatkan pH kepada 10.5. Ia terdapat dalam plasma tetapi digunakan semasa pembekuan.

Faktor VI atau Accelerin:

Faktor ini adalah produk pengaktifan hipotesis proaccelerin (faktor V).

Faktor VII atau Faktor Stabil atau Proconvertin:

Faktor ini terdapat dalam plasma dan tidak digunakan semasa pembekuan. Ia tahan haba dan boleh menahan suhu sehingga 56°C. Ia adalah protein dan kekal dikaitkan dengan prothrombin. Ia mempercepatkan pembentukan thromboplas­tin ekstrinsik atau tisu, diaktifkan oleh ekstrak yang dikeluarkan daripada tisu yang rosak. Pembentukannya terbantut selepas penggunaan Dicoumarin dan kekurangan vitamin K. Semasa pembekuan darah, proconvertin ditukar kepada menukar.

Faktor VIII atau Faktor Antihaemofilik (AHF) atau Antihaemophilic Globulin (AHG) atau Platelet Cofactor I:

Faktor ini membantu dalam pembentukan tromboplastin intrinsik dan penukaran protrombin intrinsik. Ia adalah pres­ent dalam plasma dan hilang apabila darah membeku. Ia bersifat protein dan kekal dalam hubungan rapat dengan fibrinogen. Faktor ini adalah antihemofilik. Dalam Haemophilia (penyakit bleeder’s) kecacatan bukan pada platelet tetapi ia disebabkan oleh ketiadaan faktor ini yang membantu dalam pecahan platelet dan pembebasan platelet cofactor I atau faktor tromboplastin.

Kekurangan AHG yang mengakibatkan haemofilia klasik pada lelaki adalah trans­mited sebagai sifat resesif berkaitan jantina. Badan gagal untuk mensintesis globulin penting ini kerana ketiadaan enzim khusus yang dikawal oleh gen mutan. Ia terjerap pada barium sulfat dan mempunyai berat molekul lebih daripada 200,000.

Faktor IX atau Faktor Krismas atau Komponen Tromboplastin Plasma (PTC) atau Platelet Cofactor II:

Faktor ini diperlukan untuk pembentukan tromboplastin intrinsik. Ketiadaan faktor ini membawa kepada penyakit Haemofilia yang menyuburkan dan dikenali sebagai Haemofilia C dan disebarkan sebagai resesif berkaitan jantina pada lelaki. Ia diserap oleh aluminium hidroksida, labil kepada haba tetapi agak stabil pada penyimpanan. Ia dimendakan oleh 59 peratus ammonium sulfat. Jenis penyakit ini pertama kali ditemui pada pesakit yang dinamakan Krismas dan oleh itu dinamakan faktor Krismas. Faktor ini tidak digunakan semasa pembekuan.

Faktor X atau Faktor Stuart:

Pada tahun 1959 tatanama antarabangsa telah diberikan kepada faktor ini. Secara kimia ia mempunyai banyak sifat yang serupa dengan faktor VII. Sintesisnya juga terencat selepas pentadbiran Dicoumarin. Ketiadaan faktor ini membawa kepada diatesis hemoragik ringan. Ia stabil dalam suhu bilik, tetapi musnah dengan cepat pada 56°C dalam serum.

Faktor XI atau Plasma Thromboplastin Antecedent (PTA):

Ini diaktifkan oleh faktor Hageman aktif, dan akhirnya membawa kepada pembentukan trombin. Kekurangan ini menyebabkan kecenderungan pendarahan ringan jenis D haemophiloid dan disebarkan sebagai dominan berkaitan jantina kepada kedua-dua jantina.

Faktor XII atau Hageman atau Faktor Permukaan:

Ini adalah protein dalam alam semula jadi. Borang tidak aktif diaktifkan pada sentuhan permukaan. Ini seterusnya mengaktifkan enzim pemisah protein kallikrein untuk menghasilkan kinin plasma. Kesan yang terhasil ialah peningkatan kebolehtelapan vaskular dan dilatasi saluran darah.

Faktor XIII atau Faktor Penstabil Fibrin atau Laki-Lorand (LLF):

Bentuk aktif bersama Ca ++ menukarkan bekuan fibrin lembut kepada pepejal, berserabut. Tindakannya juga mengurangkan keterlarutan bekuan dalam urea sol. Orang yang mengalami kecacatan kongenital LLF mengalami penyembuhan luka yang lemah.

Peranan Thrombin:

Thrombin ialah glikopro­tein homogen dengan berat molekul 40,000 bertindak sebagai proteinase. Ia automangkin sendiri untuk­mation dengan menukarkan plasma Ac-globu­lin kepada Ac-globulin serum aktif dan dengan melabilisasi platelet untuk mempercepatkan penjanaan tromboplastin dan membebaskan vasokonstriktor. Ia membelah hanya empat ikatan pep­tide dalam penukaran fibrino­gen kepada fibrin dan ini semua adalah ikatan antara residu arginin dan glisin.

Peranan Fosfolipid:

Phospholipid kephalin (cephalin) membantu dalam pembentukan prothrombinase. Dalam sistem intrinsik ia berada dalam faktor platelet 3 dan dalam satu ekstrinsik dalam tromboplastin tisu.

Peranan Protein:

Faktor pembekuan darah, dari V hingga XII, adalah protein plasma kebanyakannya β-globulin. Walau bagaimanapun, beberapa daripadanya adalah sama ada α-globulin atau ϒ-globulin.

Keperluan untuk sumbangan banyak faktor pembekuan terlibat dalam proses pembekuan darah. Tetapi faktor pembekuan protein plasma biasanya berinteraksi secara berpasangan. Disebabkan interaksi ini setiap faktor pembekuan seterusnya ditukar daripada bentuk tidak aktif kepada yang aktif.

Oleh kerana semua faktor pembekuan tidak sepatutnya mempunyai tindakan enzim, namun penukaran enzim ini daripada bentuk tidak aktif kepada yang aktif dimulakan dalam urutan tindakan faktor pembekuan. Proses sistem intrinsik dan ekstrinsik telah ditunjukkan secara skematik dalam Rajah 4.3.

Davie dan Ratnoff (1965) telah mencadangkan apa yang diistilahkan sebagai ‘hipotesis jujukan air terjun’ untuk menerangkan penggantian peristiwa yang berlaku dalam pembekuan darah. Setiap faktor pembekuan protein wujud dalam plasma dalam bentuk tidak aktif (proenzim) dan diaktifkan secara berurutan sehingga akhirnya trombin terbentuk yang kemudian menukar fibrinogen kepada fibrin.

Macfarlane telah mencadangkan skema pembekuan darah yang dipanggil lata enzim yang hampir sama dengan skema ‘waterfall’ (Rajah 4.4) Davie dan Ratnoff.

Penarikan Gumpalan:

Biasanya bekuan darah ditarik balik kepada kira-kira separuh isipadu awalnya dalam masa 20 hingga 24 jam. Apabila darah ditumpahkan, fibrin membentuk rangkaian seperti struktur. Platelet melekat pada rangkaian fibrin ini dan membentuk simpulan. Rangka kerja fibrin kemudiannya menjadi berpintal dan memendekkan, dan penarikan balik bekuan berlaku.

Esei # 6. Penyakit Berlaku Akibat Kecacatan Pembekuan Darah:

Kekurangan Fibrinogen atau Faktor I:

Afibrinogenaemia atau fibrinogenopenia adalah penyakit kongenital yang jarang berlaku kerana kekurangan fibrinogen. Kadang-kadang ia ditemui semasa kehamilan yang tidak normal.

Disebabkan Pengurangan Prothrombin atau Faktor II:

Vitamin K membantu dalam pembentukan prothrombin dalam hati. Vitamin K ialah derivatif naphthoquinone. Ia diserap dari usus kecil dengan kehadiran garam hempedu. Di dalam hati ia membantu dalam sintesis protrombin dan faktor VII atau faktor stabil atau proconvertin.

Dalam penyakit hati, contohnya, Cirrhosis hati, penyakit malignan hati, dan lain-lain, terdapat pengurangan sintesis protrombin dalam hati. Dalam jaundis obstruktif kerana ketiadaan garam hempedu, vitamin K tidak diserap. Oleh kerana kekurangan vitamin K, sintesis protrombin dan faktor VII berkurangan. Masa prothrombin berpanjangan dan pendarahan sering berlaku.

Disebabkan Kekurangan AHG atau Faktor VIII-Haemofilia:

Ia adalah penyakit yang berlaku pada lelaki tetapi disebarkan melalui wanita. Masa pembekuan darah berpanjangan secara luar biasa. Terdapat kecenderungan untuk berdarah teruk selepas kecederaan remeh. Sendi lutut atau siku mungkin distensi dengan darah. Kiraan platelet kekal normal. Terdapat kekurangan faktor VIII atau antihaemophilic globulin (AHG). Blood transfusion temporarily supplies AHG and stops bleeding.

Sometimes it has been observed that if bloods taken from two subjects are mixed together, coagulation time is normal although the blood coagulation time of each individual subject has got prolonged blood coagulation time. From this it has been assumed that there are two types of haemophilic subjects, one lacking in AHG and another lacking factor IX or Christmas factor or PTC.

Due to Diminution of Factors V, VII and IX-Psedohaemophilia:

In this disease there is congenital deficiency of factors V, VII and IX. The haemorrhagic condition stimulates haemophilia.

Essay # 7. Natural Inhibitors of Blood Coagulation:

To maintain blood in a fluid state in the normal condition, retarding influences coexist with positive coagula­tion-inducing -factors in the circulating blood.

Some of the ingrained safeguards against intravascular clotting are:

(a) The relative slowness of thrombin production,

(b) The unbroken continuity of the vascular endothelium and

(c) Removal of clotting intermediates by the R. E. cells. Besides these, other definite inhibitors of coagula­tion are present.

Antithrombin activities remove thrombin from blood. Antithrombin I is the thrombin-adsorbing effect of fibrin but whether it plays a role in normal blood coagulation is unknown. Antithrombin II is a factor which acts jointly with heparin. Antithrombin III is the so-called physiological antithrombin because it is present naturally and inactivates thrombin progressively. Heparin is described separately below. Antithromboplastins are present in normal blood, and one or more circulating antithromboplastins are claimed to be present.

Intravascular Clotting or Thrombosis:

It is a clot formed inside the blood vessels. Thrombus is formed due to slowing of circulation and damage of the vascular endothelium. Atheromatous patches occur in blood vessels and the vascular endothelium is damaged in some abnormal conditions. Masses of platelets are deposited in the damaged endothelium. Filaments of fibrin form also a network in this region. The platelets liberate thromboplastin.

The fibrin, entangled in the lamellae of platelets, forms the thrombus or clot. Intravascular thrombosis sometimes occurs in coronary and cerebral vessels which are called coronary thrombosis and cerebral thrombosis respectively. After surgical operations, etc., thrombosis may occur in big veins.

At first it was isolated from liver by McLean in Howell’s laboratory, hence the name. Subsequently, it has been extracted from many tissues in the body. It is anticoagulant, in vivo and in vitro. One unit of heparin is defined as the quantity of material which will prevent the clotting of 1ml of cat’s blood for 24 hours when kept in cold. Chemically it is mucoitin polysulphuric acid.

Mucoitin is a polysaccharide, composed of glucosamine, glucuronic acid and esterified sulphuric acid forming an ester with molecular weight of about 17,000. It has been shown that any substance with a high molecular weight, and being composed of polysaccharides and several SO4 groups, can act as an anticoagulant. Hirudin, found in cervical glands of the common medicinal leech (Hirudo), is a compound of this nature. Heparin is normally secreted by the mast cells.

These cells are found in blood to about 1%. They remain scattered throughout the reticulo-endothelial system and found abundantly along the course of many blood vessels, such as those of liver. Sometimes they replace the intima of the blood vessels. These cells are found to contain granules which are supposed to be the precursors of heparin.

It is doubtful whether heparin is present in normal blood in any appreciable amount and as such it probably takes no part in preventing intravascular clotting normally. Heparin helps to maintain the normal fluidity of the blood within the vascular bed. It inhibits the transformation of prothrombin to thrombin when accompanied by a plasma cofactor albumin X and neutralises the action of thrombin on fibrinogen.

iii. Fibrinolysis:

Clotted blood if kept sterile remains intact for several weeks. But if it is not kept sterile the clot breaks up. This fibrin breakdown in the clot is known as fibrinolysis and is brought about by a proteolytic enzyme in the plasma known as plasmin or fibrinolysin.

The precursor of the enzyme plasminogen (also known as profibrinolysin) is activated to plasmin by activators present in tissues, serum, urine and some bacteria. Normally fibrinolysis is prevented by the presence of another substance in the blood known as antiplasmin which remains attached to the plasma albumin.

Essay # 8. Factors Preventing and Hastening Blood Coagulation:

i. By lowering temperature, blood coagulation can be prevented.

ii. By avoiding contact with water-wettable surface and injured tissues. This prevents thrombokinase action. When blood is collected in a tube coated with paraffin, the surface not being water-wettable, the platelets will not break down and coagulation will not take place.

iii. Removal of calcium ions:

This is the commonest practice in clinical laboratories. This is done by adding citrates or oxalates of Na or K. Sodium fluoride (0.3% solution) is also used,

(b) By For­mation of a Complex Compound:

The substances used are di- and trisodium citrate and ethylene diamine tetra acetate (EDTA).

iv. Precipitation of Fibrinogen:

By adding various salt solutions in adequate amounts. When blood is mixed with one quarter of its volume of magnesium sulphate or with an equal volume of half saturated sodium sulphate solution, clotting is prevented.

v. By the Addition of Substances of Biological Origin:

Simple proteins found in some fish.

When it is injected into the veins, the coagulability of blood is reduced. [But peptone does not prevent the blood coagulation of a sample of blood in vitro]. Extracts of cray fish and nussels act in somewhat similar manner. They act by increasing secretion of heparin by the mast cells.

Mucoitin-polysulphuric acid produced by mast cells.

Hirudin (Leech extract) and the venom of certain snake. Heparin, hirudin and venom inhibit blood coagulation by inhibiting activation of prothrombin and thrombin fibrinogen reaction.

Same as heparin and hirudin.

f. Dicoitmarin or Dicoumarol:

It is chemically related to the naphthoquinone derivative. It is antagonist to vitamin K. It inhibits the synthesis of prothrombin in the liver by preventing the action of vitamin K. Dicoumarol lowers the plasma prothrombin level and depresses the activity of factor VII.

Action similar to that of dicoumarol. Its action is quick and depresses the activity of factor VII more than prothrombin.

vi. By adding azo dyes and synthetic products:

Chicago blue, trypan red, trypan blue act as anticoagulants both in vivo and in vitro.

Factors Hastening Blood Coagulation:

ii. Contact with water-wet table surface and contact with rough surface.

iii. Additions of foreign bodies into, a sample of blood (vide ‘Defibrinated blood’).

v. Addition of thromboplastin.

vi. Vitamin K injection or oral administration in high doses increases the prothrombin content of blood and increases the coagulability.

vii. Addition of calcium chloride, both in vivo and in vitro.

viii. Adrenaline injection produces constriction of blood vessels and helps in haemostatis mechanism.


1. Historical Review of Vitamin K:

Dam discovered this vitamin after studying haemorrhagic disease in chickens between the years 1930 and 1933.

2. Chemical Structure of Vitamin K:

It is a naphthoquinone derivative.

It is reported that more than one member of the K family, such as K1 K2 etc., are synthesised by green plants and bacteria. The artificially synthetic product (menadione), 2-methyl-1, 4- naphthoquinone (K3) without any side chain is 3 times more potent than the natural variety.

Two naturally-occurring vitamins K are vitamin K1 (phylloquinone, phytonadione) having a phytyl chain attached at position 3 of menadione nucleus, and vitamin K2 (flavinoquinone, farnoquinone) having a difarnesyl chain attached at position 3. Activity is apparently related to the presence of methyl group at 2 positions in the quinonoid ring. Synthetic vitamin K is called vitamin K3 (commercially menadione).

3. Properties of Vitamin K:

It is fat-soluble, heat stable, and can stand cooking. Vitamin K1 is yellow viscid oil, but vitamin K2 is a yellow, crystalline solid. The K vitamins are readily destroyed by light, alkali and alcohol.

4. Distribution of Vitamin K:

Vegetable sources are rich, such as cabbage, spin­ach, alfalfa, tomato, soya-bean, etc. It is absorbed from the in­testine with the help of bile salts. Most putrefied animals and plants contain considerable amount of vitamin K. It has also been produced synthetically.

Under normal circumstances, adequate amounts are synthesised by normal intestinal bacteria. Excessive amount of vitamin A administra­tion in certain species produces interference with bacterial synthesis of vitamin K in the intestine producing prothrombinaemia and haemorrhagic manifestations.

5. Functions of Vitamin K:

It helps to maintain the formation of normal prothrombin and factor VII in the blood and thus takes part in normal coagulation. It has been postulated that vitamin K acts as the prosthetic group to an apoenzyme to produce a holoenzyme which is involved in the clotting reactions. Prothrombin and factor VII are formed in the liver.

The principal overall effect of vitamin K is to shorten the prothrombin time. It is also postulated that vitamin K1 is an essential component of phosphorylation in both the processes of photosynthesis in green plants and animal tissues, as a cofactor necessary in oxidative phosphorylation. Loss of activity of vitamin K by ultra-violet radiation impairs oxidative phosphorylation in the mitochondria.

Bile salts are necessary for the absorption of vitamin K. In jaundice and in certain diseases of liver, when the bile secretion is defective, vitamin K fails to be absorbed resulting haemorrhages. Hepatic disease also produces hypoprothrombinaemia which is corrected by vitamin K administration. The haemorrhagic disease in the new-born is believed to be due to lack of vitamin K, since vitamin K deficiency in the new-born is due to absence of bacteria in their gut. An important therapeutic use of vitamin K is as an antidote to the anticoagu­lant drugs such as dicumarol.

6. Deficiency of Vitamin K:

Defective blood coagulation and haemorrhages.

7. Daily Requirement of Vitamin K:

Normal mixed diet supplies this vitamin in adequate amount. In the treatment of haemorrhagic diseases pro­duced as a result of vitamin K deficiency, 5 mgm is given either orally or by injection. It is believed that in adults, quite a good amount of vitamin K is synthesised by the bacteria in the gut.


BLOOD CLOTTING (HAEMOSTASIS)

The clot or coagulam is a dark -reddish-brown ‘scum’ formed mainly by a network of threads in which dead or damaged blood elements are trapped.

  • It is the property of plasma.
  • Normal blood clotting time is 3−10 min.
  • The clot inside the blood vessels is called a thrombus. A moving thrombus is called embolus.
  • In haemophilia (a sex-linked disease) the blood clotting is delayed.
  • According to Macferlane hypothesis, there are 13−factors responsible for blood clotting (or coagulation). The 4−factors are primary and 9−factors are accessory for this process.
  1. Fibrinogen
  2. Prothrombin
  3. Thromboplastin (Thrombokinase)
  4. Calcium ions

Accessory factors

(V) Labile factor (Proaccelerin) − It helps incomplete conversion of prothrombin into thrombin.

(VI) No separate entity, hence No specific name (existence doubtful).

(VII) Stable factor (Proconvertin) − It accelerates the formation of active
thromboplastin.

(VIII) Anti−haemophilic globulin (AHG)− The absence of this factor delays blood clotting causing Haemophilia−A. This type of haemophilia is most common (80%).

(IX) Plasma thromboplastin co−factor (PTC)− The deficiency of this factor causes Haemophilia−B. Approximately 20% of haemophilic patients have this type of haemophilia. The IX factor is also known as Christmas factor and Haemophilia
B is known as ‘Christmas disease’.

(X) Stuart Prower factor− It helps in the conversion of prothrombin into thrombin.

(XI) Plasma thromboplastin antecedent (PTA)− It activates the inactive christmas factor. The deficiency of this causes a rare type of bleeder-disease, called
Haemophilia -C.

(XII) Hageman’s factor or Glass factor − It converts inactive PTA into active form. It also dilates blood vessels for increasing their permeability.

(XIII) Fibrin stabilizing factor− It causes polymerization of soluble fibrin into insoluble fibrin and also inhibits depolymerization.


JAWAPAN BETUL

The p53 protein is a transcription factor that is able to suppress malignant transformation of cells by several mechanisms. It induces 1) proteins involved in DNA repair to eliminate DNA damage 2) cyclin-dependent kinase (Cdk) inhibitors to evoke quiescence (Go phase) and 3) pro-apoptotic proteins to kill cells with unrepairable DNA damage (MCQ1: B). The actin gene is not among those genes regulated by p53 (compare samples 2 to 5 in Fig. 1 MCQ2: B). The E6 oncoprotein is able to down-regulate p53 (compare samples 2 and 4 in Fig. 1), and this anti-apoptotic effect contributes to the oncogenic action of papillomaviruses (MCQ3: B). NQ01 prevents the effect of E6 (compare samples 3, 4, and 5 in Fig. 1), but possible complex formation between these two proteins was not analyzed in this experiment (MCQ4: C).

γ-Irradiation causes DNA damage and thereby increases the level of p53 in p53-positive cells (compare samples 1 and 4 in Fig. 2). The effect of dicoumarol and radicicol indicates that both NQ01 and Hsp90 is involved in the mediation of this effect (compare samples 4, 5, and 6 in Fig. 2). Both proteins are, thus, involved in DNA-damage-stimulated signaling processes leading to p53 induction (MCQ5: D). DNA repair (MCQ6: D) and inhibition of the cell cycle by blocking the phosphorylation of retinoblastoma protein by cyclin-dependent kinases (MCQ7: D, MCQ8: D, MCQ9: D). These experiments suggest that the inhibition of Hsp90 is unlikely to stop malignant cell proliferation in p53-positive myeloid leukemia patients (MCQ10: E).

Western blot analysis of human colon carcinoma cells transfected with p53, NQO1, and E6 cDNAs (for details see the text).

The effect of γ-irradiation, dicoumarol, and radicicol treatment on myeloid leukemia cells (details in the text).


Note the following:
(a) kulit (b) Fagosit
(c) B-cells (d) Keradangan
(e) Antibodi (f) T-cells
(g) Demam (h) Antimicrobial proteins
(i). NK-cells (j) Secretions
Identify the factors involved in 2nd line of defense.

Assertion: Cancer cells are virtually immortal until the body in which they resides dies.

Sebab: Cancer is caused by damage to genes regulating the cell division cycle.


Bahan Dan Kaedah

Kultur sel

Rat basophilic leukemia (RBL)-2H3 cells were grown in DME supplemented with 16% FCS and 1 mM l -glutamine. CHO cells were cultured in DME supplemented with 10% FCS.

Antibodies and Other Reagents

NAD + , NADP + , NADH, BFA, and GAPDH from skeletal rabbit muscles were obtained from Sigma Chemical Co. (St. Louis, MO). Tissue culture materials were from GIBCO BRL (Grand Island, NY) and Seromed (Berlin, Germany). GTP and ATP were from Boehringer Mannheim (Mannheim, Germany). Rabbit anti–α-mannosidase II (Man II) antibody was provided by K. Moremen (University of Georgia, Athens, GA), and a rabbit anti–β-COP antibody by J. Donaldson and J. Lippincott-Schwartz (National Institutes of Health, Bethesda, MD). All other chemicals were obtained from commercial sources at the highest available purity. BFA was stored at −20°C in stock solutions in DMSO. Dicumarol was prepared before use as an aqueous solution.

Cell Permeabilization

RBL (grown in glass chamber slides) were placed on ice and immediately washed with the permeabilization buffer (PB: 25 mM Hepes-Koh, pH 6.95, 125 mM KOAc, 2.5 mM Mg[OAc]2, 10 mM glucose, 1 mM DTT, 1 mM EGTA, and 0.5 μM taxol). Cells were then incubated with 3 U/ml of streptolycin O (SLO) (Biomerieux, Marcy l'Etoile, France), previously activated for 5 min at room temperature in PB for 8 min on ice. Unbound SLO was removed and cell monolayer was washed with cold PB, and then treated with permeabilization buffer supplemented with 1 mg/ml rat brain cytosol, 1 mM ATP, 250 μM UTP, 2 mM creatine phosphate, 7.3 U/ml creatine phosphokinase at 37°C for between 20-30 min (in the presence of the indicated treatments). To check the extent of permeabilization, cells were stained with Trypan blue (and propidium iodide) and the leakage of the cytosolic enzyme lactic dehydrogenase was measured. With the adopted schedule of SLO treatment, 95% of cells were stained with Trypan blue or propidium iodide and >80% of the lactic dehydrogenase activity was recovered in the supernatant of the permeabilized cell monolayer. Rat brain cytosol was prepared according to Malhotra et al. (1989).

BFA-dependent ADP-Ribosylation

ADP-Ribosylation in Permeabilized Cells.

RBL cells were plated in 24-well plates and used after 24 h at 90% confluency (300,000 cells/well per 250 μl). They were permeabilized as described above and then exposed for 20 or 60 min to PB containing 500 μM tymidine, 30 μM 32 P-NAD + (3 μCi/sample) and, where specified, BFA. At the end of the incubations the supernatant and the cell proteins were precipitated with 10% TCA, dissolved in sample buffer, and separated on SDS-PAGE. The radioactivity bound to BARS-50 and GAPDH was evaluated by fluorography.

ADP-Ribosylation of Cytosol.

Cytosol and membranes were prepared from rat brain as described (De Matteis et al., 1994). Cytosol (10 mg/ml) and salt-washed membranes (2 mg/ml) were incubated in the presence or absence of 200 μM NAD + or 100 μM BFA or both for 60 min at 37°C. Under these experimental conditions the ADP-ribosylation of BARS-50 (evaluated in parallel experiments run in the presence of 32 P-NAD + ) was maximal (>90%), whereas that of GAPDH was only partial (3–4%). No other proteins were detectably ADP-ribosylated by BFA (see Fig. 3). At the end of the incubation the samples were centrifuged at 100,000 g for 60 min and then the supernatants (cytosol) were dialyzed for 16 h at 4°C and used in immunofluorescence experiments in permeabilized cells as described below.

Immunofluorescence and Lectin Staining

Intact or permeabilized RBL cells were fixed in 4% paraformaldehyde in PBS at room temperature for 10 min, quenched in 10 mM NH4Cl for 10 min, washed in PBS, and permeabilized with 0.05% saponin, 0.2% BSA in PBS for 30 min at room temperature. The cells were stained with FITC-conjugated helix pomatia lectin (100 μg/ml in PBS containing 0.2% BSA) for 45 min or incubated with primary antibody for 1 h at room temperature, washed thoroughly with PBS, and incubated with specific FITC-, TRITC-, or Cy3-conjugated secondary antibody for 30 min at room temperature. After thorough washing, slides were mounted in Mowiol 4-88 (Calbiochem-Novabiochem, La Jolla, CA) and examined using a microscope equipped with a Plan-Neofluar 40× objective (Axiophot Carl Zeiss, Thornwood, NY). RBL or CHO cells grown in glass chamber slides (Nunc, Roskilde, Denmark intact or permeabilized as described above), were fixed in 4% paraformaldehyde in PBS (pH 7.4) at room temperature for 10 min, quenced in 10 mM NH4Cl for 10 min and then washed in PBS and permeabilized with 0.05% saponin, 0.2% BSA in PBS for 30 min at room temperature. Cells were stained with FITC-conjugated helix pomatia lectin (100 μg/ml in PBS containing 0.2% BSA) for 45 min or incubated with primary antibody for 1 h at room temperature, washed thoroughly with PBS and incubated with specific FITC-, TRITC-, or Cy3-conjuagted secondary antibody for 30 min at room temperative as described earlier (Buccione et al., 1996).

Mikroskopi Elektron

Cells were fixed with 2% glutaraldehyde in PBS (pH 7.4), postfixed with reduced osmium (1% of OsO4 and 1.5% of potassium ferrocianide in 0.1 M cacodilate buffer, pH 7.4), and embedded in Epon 812 as described earlier (Buccione et al., 1996).

Preparation of BARS-50–enriched Cytosolic Fractions

Rat brain cytosol (Malhotra et al., 1989) was precipitated with 35% saturated (NH4)2JADI4. The precipitate was dissolved in 25 mM Hepes, pH 8.0, containing 5% glycerol, 0.5 M (NH4)2JADI4 and 1 mM DTT (buffer A) and applied to a phenyl sepharose HP column (Pharmacia Biotech, Piscataway, NJ) equilibrated with buffer A. Proteins were eluted with a linear gradient of buffer A minus (NH4)2JADI4. The fractions containing BARS-50 were identified by the BFA-dependent ADP-ribosylation assay (De Matteis et al., 1994). These fractions (containing a 45-fold enriched BARS-50 and no GAPDH) were concentrated and dialyzed against buffer B (25 mM Hepes, pH 7.2, 50 mM K, and 1 mM Mg acetate) overnight. The final protein concentration was 2–3 mg/ml.


12th Class Biology Genetics Multiple Allelism

More than two alternative forms (alleles) of a gene in a population occupying the same locus on a chromosome or its homologue are known as multiple alleles.

Characteristics of multiple allelism

(a) There are more than two alleles of the same genes.

(b) All multiple alleles occupy the corresponding loci in the homologous chromosomes.

(c) A chromosome or a gamete has only one allele of the group.

(d) Any one individual contains only two of the different alleles of a gene, one on each chromosome of the homologous pair carrying that gene.

(e) Multiple alleles express different alternative of a single trait.

(f) Different alleles may show codominance, dominance-recessive behaviour or incomplete dominance among themselves.

(g) Multiple alleles confirm to the Mendelian pattern of inheritance.

Examples of multiple allelism : A well known example of a trait determined by multiple alleles is the blood groups in man and skin colour. Other example are eye colour in Drosophila, colour of wheat kernel, corolla length in Nicotiana, Coat colour in Cattle etc.

Blood groups in man

Blood proteins : According to Karl landsteiner (1900) a Nobel prize winner, blood contains two types of proteinous substances due to which agglutinations occurs.

(1) Agglutinogen or antigen : It is a protein found on the cell membrane of RBC&rsquos.

(2) Agglutinin or antibody : This the other proteinous substance, found in the plasma of the blood.

Whenever the blood of a person receives the foreign proteins (antigen) his blood plasma starts forming the antibodies in order to neutralize the foreign antigens.

Agglutinations : Two types of antigens are found on the surface of red blood corpuscles of man, antigen A and B. To react against these antigens two types of antibodies are found in the blood plasma which are accordingly known as antibody &ndash anti-A or a dan anti-B or b. Agglutination takes place only when antigen A dan antibodi a occur together or antigen B dan antibody b are present in the blood.

Under such condition antibody a bertindak balas dengan antigen A and makes it highly sticky. Similarly antigen B in presence of antibody b become highly sticky with the result RBC&rsquos containing these antigens clump to form a bunch causing blockage of the capillaries. Agglutination in blood is therefore antigen-antibody reaction.

Types of blood groups

ABO blood group : Landsteiner divided human population into four groups based on the presence of antigens found in their red blood corpuscles. Each group represented a blood group. Thus there are four types of blood groups viz. A, B, AB and O. He observed that there was a reciprocal relationship between antigen and antibody according to which a person has antibodies for those antigens which he does not possess.

Blood groups of man with antigen and antibodies

Type of blood group

% in society

M, N blood group : K. Landsteiner and A.S. Wiener discovered that antigen M,N or both MN are also found on the surface of red blood corpuscles of human beings. No antibodies are however formed in the blood plasma for these antigens.

In this way when blood with M group is injected in rabbit it will produce antibodies in the blood serum which will bring about agglutination with blood group M and MN but not with blood of N group. In the same way on injecting blood of N group into the rabbit it will bring about agglutination with blood group N and MN and not with blood having blood group M.

Blood transfusion

Blood transfusion is best done in the persons of same blood group. At the same time it is possible to know in which different blood groups the blood transfusion can be made possible.

Persons with blood group AB are called universal recipients because both antigens A and B are found in their blood and the two antibodies &lsquoa&rsquo and &lsquob&rsquo are absent. Therefore, such persons can receive blood of all the blood groups.

In the same way persons who have blood group [<^<>>]are universal donors as they lack both the antigens and [R<^<>>] person can donate to Rh + person as well as Rh &ndash person but Rh + person cannot donate blood to Rh &ndash person. But at the same time such persons can not be given the blood of any other blood group except blood group O because their blood possesses both the antibodies &lsquoa&rsquo and &lsquob&rsquo. Persons belonging to blood group A and B contain only one antigen and one antibody against it, in their blood. Such persons can therefore receive blood either of the blood group of their own or the blood group O.

A place where blood of different blood groups is safely stored in bottles for emergency use, is called blood bank. Blood after proper testing is stored in a sealed bottle at a definite temperature [(4<>^circ -6<>^circ c)] to be preserved for a definite time period.

Artificial anticoagulants are used to prevent blood clotting in the blood banks. These anticoagulants are added to the blood preserved in bottle. Such anticoagulants include sodium citrate, double oxalates (sodium and ammonium), dicumarol and EDTA (ethylene diamine tetra acetic acid). The whole blood in this way can be stored for a maximum period of 21 days.

Inheritance of blood groups

Blood groups in human are inheritable trait and are inherited from parents to offsprings on the basis of Mendel&rsquos Laws. Blood group inheritance depends on genes received from parents. Genes controlling blood group in man are three instead of two and are called multiple alleles. All these three genes or alleles are located on the same locus on homologous chromosomes. A person can have only two of these three genes at a time which may be either similar or dissimilar in nature. These genes control the production of blood group/antigens in the offspring. The gene which produces antigen A is denoted by [<^>,] gene for antigen B by [<^>] and the gene for the absence of both antigens by [<^>.]it is customary to use the letter I (Isohaemagglutinogen) as a basic symbol for the gene at a locus. Based on this, six genotypes are possible for four blood groups in human population.


Chemical Biology, Protein Engineering Led to Targeted HBV Treatment Advances

Two key aspects of the HBV lifecycle vital to the development of chronic infections are the creation of a viral minichromosome in the form of cccDNA and the expression of the regulatory HBx protein.

Responsible for nearly half of all cases of hepatocellular carcinoma, chronic hepatitis B virus (HBV) is a worldwide concern and a major public health problem. Through rigorous research, investigators have identified 2 key aspects of the HBV lifecycle essential to the development of chronic infections: the establishment of a viral minichromosome in the form of covalently closed circular (ccc) DNA and the expression of the regulatory hepatitis B virus X (HBx) protein.

Researchers penned an overview of recent advances in the scientific understanding of cccDNA and the mechanistic and functional roles of HBx in a recent article in ACS Infectious Diseases.

Artikel berkaitan

cccDNA Overview

According to researchers, the successful establishment of cccDNA is “critical” for HBV replication. Despite this, the specific host mechanisms that act to convert relaxed circular (rc) DNA into cccDNA are poorly understood.

Scientific advances have allowed researchers to begin identification of the roles played by various host enzymes in cccDNA generation, either through rationally testing the enzymes involved in DNA metabolism or by RNA silencing. Additional research has identified similarities between the antisense strand of rcDNA structure and 5′ flap structures, formed during Okazaki fragment maturation, as a contributor to the formation of cccDNA, and RNA silencing screening studies also identified several DNA polymerases — α, η, κ, and λ — that mediate cccDNA establishment.

Taken together with the recent confirmation of DNA ligases I and III as crucial in converting rcDNA to cccDNA and the identification the role of topoisomerase 1 and 2 in cccDNA synthesis, these factors may represent a novel therapeutic avenue for the treatment of chronic HBV infection, according to the researchers.

Further biochemical and biophysical studies are required to define the role of cccDNA-bound hepatitis B core antigen, which would prove “invaluable” for the study of both cccDNA and HBx.

HBx Overview

HBx is the primary effector protein encoded by HBV. Although numerous human proteins have been identified as potential interactors with HBx, “relatively few” of these interactions have known functional outcomes, representative of the ambiguity that surrounds the poorly understood structure of the protein.

Within the nucleus, HBx performs dual roles: redirecting host transcription factors, including p53, NF-κB, and CREB, to change the expression of a “wide variety of gene families,” and initiating virus replication via the stimulating transcription of cccDNA. Although HBx is critical for both cccDNA transcription and the development of viremia in vivo, the HBx protein itself is not packaged in the mature virion. According to the researchers, this raises the question of how, during initial HBV infection, HBx can be expressed without being already present in the cell.

“Current theories propose that HBx may be transcribed from rcDNA or dslDNA before or during conversion into cccDNA, though one recent report identified HBx mRNA in both cell culture derived virus preparations and HBV patient plasma, suggesting that it may indeed be packaged into the virion,” the researchers noted.

Yael David, PhD, and colleagues went on to describe the more well-known HBx functions and regulatory mechanisms.

HBx and CRL4. Until recently, the structural basis and functional significance for the interaction between HBx and damaged DNA-binding protein 1 (DDB1) was unknown however, research has found that DDB1 works as an obligate adaptor protein for the cullin-RING ligase 4 (CRL4) E3 ligase complex. Later proteomic studies identified the HBx-mediated degradation of the structural maintenance of chromosomes. More targeted in vitro and cell-based studies are needed.

HBx and chromatin modifications. According to the researchers, decades of study have illustrated that HBx is able to redirect the cellular machinery responsible for the erasure or deposition of histone posttranslational modifications, to produce the active chromatin landscape on cccDNA. Specific chromatin immunoprecipitation-based studies found that, within HBx-deficient infections, there was an “increased occupancy of the histone deacetylases Sirt1 and HDAC1” on cccDNA. This suggests that HBx may either outcompete for binding sites or mediate their degradation. Ultimately, the ability of HBx to recruit diverse proteins to cccDNA “raises questions about the mechanism by which it mediates such interactions.”

Posttranslational modifications of HBx. To modulate its functions, HBx itself is posttranslationally modified, adding an additional layer of complexity to HBx biology and regulation. Recent studies have described the biochemical roles for both HBx posttranslational modifications and the enzymes that deposit them, which may eventually provide insight into so-called novel pathways to indirectly target the HBx function. In the future, a more detailed analysis of HBx structure and posttranslational modifications in vivo will be required, allowing future in vitrostudies to use more physiologically relevant conditions.

Advances in HBx and cccDNA-Targeting Treatments

To date, a significant body of work has highlighted the relative importance of both cccDNA and HBx in HBV replication and in the persistence of chronic infection. In this vein, recent studies have reported a variety of approaches that can target viral elements through the use of small molecule or biologic tools. Methods range from rationally targeted approaches, backed by established and recently developed methodologies, to “target-agnostic high-throughput screens.”

Current genome editing methods allow for the “relatively facile, locus-specific” generation of double-stranded DNA breaks. This generation led to theories suggesting that a similar approach could be used to target cccDNA for degradation. Several independent groups reported relative successes, but barriers still remain that prevent the clinical use of this approach — specifically, the lack of clinical trials surrounding the practice of gene-editing therapy.

Hepatitis B virus has a 10-fold higher mutation rate compared with conventional DNA viruses as a result, resistance mutations may rapidly rise in conjunction with strong selective pressure. In addition, an approximately 8% sequence divergence at the DNA level may make it difficult for researchers to development a therapy capable of targeting each HBV genotype. Perhaps most importantly, though, is that the generation of a double-stranded DNA break in cccDNA would result in the generation of dslDNA, which could lead to genome integration by host DNA and the promotion of oncogenesis.

Despite these potential pitfalls, genome editing remains an attractive approach, useful in both research and in the clinic setting.

The lifecycle of HBV is complex, creating a challenging environment for study however, this complexity also opens up several pathways that may be adapted for use within high-throughput screening approaches. Multiple recent studies have reported successes through promising screening approaches, several of which specifically targeted HBx functions or restricted cccDNA expression.

One example was the identification of a high-throughput screening that advantageously leveraged the documented role of HBx in inhibiting certain RNA silencing pathways. Using a computational model to generate a 3-dimensional structural model of HBx, investigators identified potential binders, which were then used to screen for the reversal of HBx-mediated RNA silencing suppression. One compound, dubbed “IR415,” was generated additional studies will be necessary to determine whether IR415 disrupts any other aspects of HBx function.

Even more recently, researchers identified another HBx targeting molecule using a split luciferase screening assay. Nitazoxanide, a broad-spectrum, anti-infective agent used typically to treat parasitic infections was identified as a potential disruptor. Future studies should examine this interaction.

Most recently, investigators reported a chemical screen used to identify inhibitors of episomal DNA expression. Dicoumarol, a small molecule, was shown to decrease episomal DNA expression, which was validated using HBV-infected primary human hepatocytes. A dose-dependent depletion of cccDNA was observed, suggesting that dicoumarol may be the basis for future drug development.

Looking Forward: Future Perspectives in HBV

The use of interdisciplinary techniques, in particular, have led to significant advances in the understanding of cccDNA establishment and regulation, as well as the mechanisms of HBx function however, questions still remain regarding these “key components” of HBV.

One difficulty in the study of HBx is the scarcity of methods used to manipulate or modulate native HBx within the context of an active HBV infection however, the use of small molecules as described may represent a unique opportunity to chemically address these methodological challenges. Similarly, the use of protein engineering strategies to better study HBx both in vivo and in vitro should be developed protein fusion methods have been reported in the literature, but efforts must continue to build on this process.

Despite significant progress in identifying the elements involved in the establishment and repair of cccDNA, structural and regulatory component details remain “enigmatic,” according to the authors. Recent efforts have been made to characterize the landscape of post-translational modifications of cccDNA, but many of these efforts rely on chromatin immunoprecipitationplus next-generation DNA sequencing, which has several shortcomings — availability, inherent target bias, and relatively low throughput among them.

Finally, the development of increasingly sophisticated methods to study chromatin biology in HBV-susceptible cell lines may establish a platform allowing for the interrogation of key biochemical questions regarding cccDNA. Specifically, the development of a method for the reconstruction of a cccDNA model for use in in vitro biochemical and biophysical studies might provide “crucial insight into the mechanisms behind recognition and recruitment of host factors onto cccDNA,” the researchers noted.

“Continued efforts in recent years have revealed critical details about the cccDNA life cycle and the HBx function that may potentially serve as the basis for novel therapeutic approaches,” David and colleagues concluded. “[O]ngoing research is needed to further build upon these advances. Chemical biologic and protein engineering techniques are perfectly poised to fully illuminate these two cryptic yet indispensable components of chronic HBV infection.”


Life Sciences Questions and Answers – Respiration – 2

This set of Life Sciences Questions and Answers for Freshers focuses on “Respiration – 2”.

1. What is Respirasome?
a) The supramolecular complex of complex I, II, and III
b) Respiratory center of the body
c) Complex III and IV of the electron transport chain
d) The intermediate complex formed during oxidative phosphorylation
View Answer

2. FeS and FAD are the prosthetic groups of ______
a) Complex I
b) Complex II
c) Complex III
d) Complex IV
View Answer

3. Mark the INCORRECT statement about Coenzyme Q?
a) It shows ubiquitous in nature
b) It is also known as ubiquinone
c) Q refers to the quinone chemical group
d) It has a protein bound prosthetic group
View Answer

4. Out of the following, which one is not the inhibitor of the electron transport chain?
a) Rotenone
b) Antimycin A
c) Cyanide
d) Malonate
View Answer

5. Name the physiological uncoupler which stops ATP synthesis.
a) 2, 4-dinitrophenol
b) Dicoumarol
c) FCCP
d) Thermogenin
View Answer

6. What is the total yield of ATP from complete oxidation of one molecule of glucose?
a) 32
b) 10
c) 8
d) 40
View Answer

7. Fermentation is similar to anaerobic respiration.
a) True
b) False
View Answer

8. What is the Cori cycle?
a) Glyoxylate cycle
b) Gluconeogenesis
c) Lactic acid cycle
d) Citric acid cycle
View Answer

9. Which of the following is CORRECT for the Pasteur Effect?
a) Utilization of glucose for fermentation
b) Increased glucose consumption by yeast in anaerobic condition
c) Fermentation favors aerobic condition more than anaerobic
d) Increased consumption of glucose by yeast in aerobic condition
View Answer

10. What is the Warburg effect?
a) Shows increased glycolysis in Cancer cell
b) Disease caused by pesticide
c) Blockage of ATP synthesis
d) Inhibitor of glycolysis
View Answer

11. Mark the correct equation for Respiratory quotient?
a) RQ = O2 produced/Co2 dimakan
b) RQ = Co2 produced/ O2 dimakan
c) RQ = H2O produced/ Co2 dimakan
d) RQ = H2O produced/ O2 dimakan
View Answer

Sanfoundry Global Education & Learning Series – Life Sciences.

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