- •16. Neoplasia
- •16.1. Name the basic kinds of tissue growth changes.
- •16.3. Why tumoral process is considered to be the general biological phenomenon?
- •16.4. Are there features in character of tumoral process in humans and different kinds of animals?
- •16.5. What are the basic distinctions between benign and malignant tumours?
- •16.6. What are methods of experimental studying of tumours?
- •16.7. Name principal causes of malignant tumours occurrence.
- •16.8. Who and how for the first time has proved a role of chemical factors in occurrence of malignant tumours?
- •16.9. How are chemical carcinogens classified?
- •16.10. Give the examples of carcinogens of a natural and artificial origin.
- •16.11. Characterize carcinogenic action of polycyclic aromatic hydrocarbons (pah).
- •16.12. What is the feature of carcinogenic action of aromatic amines?
- •16.13. What is carcinogenic influence of nitrozo-compaunds characterized by?
- •16.14.Give examples of carcinogenic action of products of mushrooms life.
- •16.15. What meaning is put in concept "endogenous carcinogens"?
- •16.16. In what experiences possible participation of hormones in occurrence of malignant tumoral growth is proved?
- •16.17. What are chemical carcinogens of direct and indirect action? Give their comparative characteristic.
- •16.18. What properties of chemical substances cause their carcinogenic action?
- •16.19. What stages passes chemical carcinogenesis? What is their essence?
- •16.20. What is an explanation of the phenomenon of a tumoral progression?
- •16.21. What physical factors can matter in occurrence of malignant tumours?
- •16.22. Name the basic laws of carcinogenic action of an ionizing radiation.
- •16.23. What is "plastic" carcinogenesis? What are its features?
- •16.24. Who proved a role of viruses in occurrence of tumours and in what experiments?
- •16.25. What dna-containing viruses are oncogenic for animals and human?
- •16.26. What rna-containing viruses are oncogenic for animals and human?
- •16.27. Name stages of virus oncogenesis.
- •16.28. Name factors on which transforming action of viruses on a cell depends.
- •16.29. What are the viral oncogenes?
- •16.30. What are protooncogenes?
- •16.31 How are virus oncogenes and protooncogens classified?
- •16.32. What are cellular oncogenes? Name the basic mechanisms of transformation of protooncogenes into cellular oncogenes.
- •16.33. What are antioncogens?
- •16.34. What molecular mechanisms can underlie in virus oncogenesis?
- •16.35. What molecular mechanisms can be connected carcinogenesis, caused by action of chemical and physical factors?
- •16.36. Name features of growth of malignant tumoral cells in vitro conditions.
- •16.37. Name the basic features of growth of malignant tumours in vivo.
- •16.38. With what speed do malignant tumours grow? What factors is it defined by?
- •16.39. What violations of metabolism characterize malignant tumours?
- •16.40. What is invasiveness of tumours? How do malignant cells sprout in surrounding tissue?
- •16.41. What is metastasing? How is it carried out?
- •16.42. How do the tumours influence on an organism as a whole? Why cancer cachexy do develops?
- •16.43. What factors of an organism influence development of malignant tumours?
- •16.44. What mechanisms of antineoplastic protection exist in an organism?
- •16.45. Name the basic pathogenetic approaches to treatment of tumours.
16.26. What rna-containing viruses are oncogenic for animals and human?
All oncogenic RNA-containing viruses belong to retrovirus family. Their general property is presence of a gene coding structure of revertase enzyme in virus genome, known still as return transcriptase, or RNA-dependent DNA-polymerase. This enzyme provides synthesis of two-spiral DNA on a matrix one-spiral RNA. That is why DNA-copy of retrovirus which has received the name of DNA-provirus is formed.
Depending on oncogeneicity retroviruses are divided into two groups.
I. Acutetransformate retroviruses. They are very oncogenic, cause development of tumours after the short latent period. These viruses have oncogen in the genome, therefore in a basis of transformation of cells in tumoral lays an epygenome mechanism. Viruses, in particular, are concerned to the specified group of sharp leucosis of birds, mice and sarcoma of Raus of hens.
II. Slowtransfomate retroviruses. Cause development of tumours after the long latent period. These viruses do not include oncogen; therefore the basic mechanism of their transforming action is mutational. Viruses, belong to this group are lympholeucosis viruses.
The oncogenic retrovirus of the person is the virus of the T-cellular leucoma-leucaemia. It is transferred from the person to the person during long intimate contacts, blood transfusion. It is necessary to note, that this lymphotropic virus has a big similarity to the human immunodeficiency viruses (HIV) causing AIDS.
16.27. Name stages of virus oncogenesis.
I. Reception of the virus. There is an interaction of a virus particle to the certain structures of a plasmatic membrane of a cell (receptors). Absence of corresponding receptors is explained specific immunity to a virus infection.
II. Undressing and penetration of a virus into a cell (internalization).
III. Association (integration) of virus genome with the genome of cell. It is the central and obligatory stage of virus oncogenesis. In case of DNA-containing oncoviruses there is an embedding of DNA virus in DNA of a cell, in case of RNA-containing viruses - DNA-provirus, formed under influence of revertase enzyme.
IV. Constant stay (persistention) of a virus in genome of a cell. Thus the virus is made multiple copies together with a cell. Such current of a virus infection refers to abortive. The abortive current is an indispensable condition of transformation of a cell in tumoral under influence of a virus.
V. Tumour transformation of a cell.
VI. Promotion.
VII. The tumoral progression (see question.16.19 and 16.20).
16.28. Name factors on which transforming action of viruses on a cell depends.
I. Factors which are defined by properties of a virus. So-called structural deficiency of a virus, in particular, is concerned to them. Structurally defective viruses which during duplication and formations of virus particles have lost a part of the genome. They are capable to get into a cell and to be united with its genome; however they are not capable to reproduction. In this case the unique variant of a virus infection is its abortive current which increases probability of transformation of a cell under influence of structurally defective viruses.
Besides for mechanisms of oncogenic actions of viruses the presence or absence in their genome of virus oncogen matters has a great importance.
II. Factors which are defined by properties of cells. They include the presence of corresponding receptors on surfaces of cells, the period of a cellular cycle during which the virus gets into the cell. Integration of a virus genome with cells genome is possible only in a synthetic phase (the S-phase) or during, directly previous it (the end of phase G1,). In particular such circumstance that high-differentiated cells which have lost ability for duplication are steady against action of oncogenic viruses is explained.
Besides the cell becomes sensitive to oncogenic viruses if in it there are no conditions for synthesis of all proteins of a virus particle. In such conditions the reproduction of a virus and a virus infection is impossible proceeds on abortive to the type at which the probability of transformation of a cell increases. The similar phenomenon has received the name of functional deficiency of a virus.