Question

Match the following options:

List I	List II
1.HIV	i.Host
2.Pilus	ii.Prophage
3.Virus penetration	iii.Retroviridae
4.Lysogeny	iv.Polyhedral virus

(a) 1 - i, 2 - ii, 3 - iii, 4 - iv
(b) 1 - i, 2 - iv, 3 - iii, 4 - ii
(c) 1 - iv, 2 - iii, 3 - ii, 4 - i
(d) 1 - iii, 2 - iv, 3 - i, 4 - ii

Answer 1

Hint: Virus is classified based on the species of organisms they infect. They are obligate parasites as without an organism to provide shelter and nutrients, they remain in a dormant state. Some viruses use certain appendages on bacteria for adhesion. Upon infection, they can kill the organism or just replicate increasing its population.

Complete answer:
- HIV or Human Immunodeficiency Virus is an enveloped lentivirus within the family retroviridae. It causes deadly AIDS or Acquired ImmunoDeficiency Syndrome, where a person experiences a marked deficiency in the cellular immune response. This occurs due to a significant drop in the subpopulation of T- cells.
- Pilus is an appendage made up of contractile proteins protruding from several gram- negative bacteria. Polyhedral viruses like Bacteriophage use pilus to identify and bind to the bacterial cell surface.
- The virus uses specific receptors on the cell surface for attachment. The cell to which it binds is referred to as the host. This attachment is succeeded by virus penetration into the host. It does so by various methods like directly penetrating its genome or fusing with the host’s plasma membrane or through receptor- mediated endocytosis.
- A bacteriophage has two different types of life cycles- The lytic cycle or the Lysogenic cycle. In the lysogenic cycle, the viral DNA is inserted into the host’s DNA and reproduces as the host’s DNA replicates. For this, it first inserts its genetic material into the DNA of host cells. This stage is referred to as the prophage stage. A cell bearing prophage is known as a lysogen.
So, the correct answer is ‘1 - iii, 2 - iv, 3 - i, 4 - ii.’

Note:
- The lysogenic cycle of bacteriophage in the host cell does not result in its death. In fact, a lysogenic phage can remain in this state for numerous replication of host cell DNA until it excises itself from the host DNA and undergoes a lytic life cycle.
- The lytic life cycle causes the death of the host as it results in its lysis or rupture. Such phages are known as virulent phages. E.g. T4 phages.