Question

What are viruses composed of? How do they differ from cellular life? What is their basic life cycle? Describe lytic and lysogenic cycles in bacteriophages. What are three hypotheses about how viruses originated?

Answer 1

● Viruses are composed of:

1. Core of nucleic acid

2. Nucleic acid core surrounded by capsid (protein coat)

(3. Sometimes, protein capsid is surrounded by an additional coat called the lipid bilayer )

● virus differs from cellular life in following ways:

1. Viruses are non-living particles.

2. They Cannot generate ATP

3. They Need living-host for survival and reproduction.

● Basic life cycle of a virus:

1. Attachment: attach itself to the target cell.

2. Penetration: the targeted cell engulfs the virus by endocytosis.

3. Uncoating : viral contents are released in the cell.

4. Biosynthesis: viral RNA enters the nucleus for replication.

5. Assembly: new viral particles are assembled.

6. Release: newly produced viral particles are released in the extracellular fluid (the host cell, which is not killed in the process will continue to produce new viral particles)

● lytic cycle - This cycles results in destruction of the infected host cell after the bacteriophage replicates.

Lysogenic cycle - In this cycle, the nucleic acid of the bacteriophage gets incorporated with that of a host, followed by reproduction of the resulting prophage.

● Three Hypothesis regarding virus origins:

1. Virus first hypothesis: It states that viruses existed as self-replicating units in a precellular world and contributed to the rise of cellular life.

2. Regressive or reduction hypothesis: It states that viruses are remnants of cellular organisms.

3. Progressive or escape hypothesis: It states that viruses arose from genetic materials (RNA or DNA) that break free from a host cell.