Question

1. List 3 viral classes based on their morphology.
2. What is the difference between lytic and lysogenic cycles?
3. How can you grow viruses in the laboratory?
4. _________________________ viruses become integrated in to the host cell’s DNA and induce tumors.

Answer 1

Based on their morphology, viruses are of three types

A) Helical - Nucleic acid and capsomere are coiled and form a spiral structure. Example- Tobacco Mosaic Virus

B) Icosahedral - having 20 facets, 12 corners and 30 edges whose symmetry is same as of body diagonal of cube. Example- Adenovirus

C) Complex or Binal - Whose head is Icosahedral and tail is helical, exhibits this style of symmetry. Example- T2 phage

Difference between lytic cycle and lysogenic cycle

Lytic cycle	Lysogenic cycle
Lytic cycle involves T even series of phages	it involves lambda phages
There is no integration be of viral DNA with host DNA	Here Integra of vir DNA with host DNA takes place
Host cell get lysed	Host cell doesn't lysed
The entire cycle can taken a relatively short time than lysogenic cycle	It takes relatively a long time

Viruses can be grown in laboratory in embryonated chicken eggs. Steps are as follows

1) The egg which has embryo , has air space at larger end.

2) Then at larger end, the shell is cut and removed

3)As a result of it , adjacent membrane is exposed

4) Then membrane is removed and virus to be grown is taken in dropper and simply spreaded over the exposed embryo.

5) Soon after inoculation, it is sealed with cellphane membrane and left it for incubation as in hatching

6) Virus started infecting embryo and developed pock mark which the result of growing viral population. This pock marks are visible against transparent background.

Oncoviruses become integrated in to host cell's DNA and induce tumors. As Adenovirus can cause tumors, Epstein-Barr virus causes some neoplasia in human. Oncovirus has certain gene elements which brings the malignant characters of cell.