Question

2. Answer the following about Viruses with a simple 2-3 sentence (or more if you needed)

a.Describe the importance of viruses ecologically, evolutionarily, and with respect to human disease

b.Explain the difference between enveloped and nonenveloped viruses.

c. Compare and contrast the viral replicative (lytic) vs. the lysogenic cycle.

d. Discuss the three hypotheses for the origin of viruses and explain how they continue to evolve.

e. Describe some of the problems caused by emerging viral diseases, and give at least one example.

f. Explain how the diversity of viruses is related to their genetic material.

Answer 1

Viruses are obligate intracellular parasites, that are yet not confirmed as a living entity because of its dependence on a living cell for replication. It also doesn't carry out any metabolic process on its own and it doesn't possess the ribosomal machinery for synthesizing its protein. It is classified as Capsid-encoding organisms it has simply the following components

1. genomic material (DNA/RNA)
2. protein capsid - encloses the genomic material
3. lipid envelope - helps in attachment to host cell

a. Most of the viruses are bacteriophages that replicates only within the bacterial cells. Hence, it kills the pathogenic bacterium and recycles the carbon and other components embeded in those organisms. Viruses also destroys the algal blooms which are harmful for the aqatic organisms, thereby saving the marine life. As like other organisms virus evolves through period which leads to failure of a vaccine developed at a particular period for a specific virus in the later stages of life. And they are also considered to be one of the rapidly evolving organisms.

b. The lipid envelope is not present in all viruses, those which possess this component were called envelped virus while others are called non-enveloped virus.

c. Virus particles has two cycles of lifecycle in the host cell

1. Lytic cycle: Here, as soon as the virus particle enters the host cell, it replicates its genome and produces other components needed for virus particle assembly by hijacking the host metabolic processes. When the needed components are produced, the virus particles assembles and evades the host cell by rupturing the cell membrane. This cycle increases the reproduction rate of the virus.
2. Lysogenic cycle: Here, the virus genome gets integrated into the host cell genome and remain as a prophage for a longer period of time causing no harm to the host cell. The virus particle then turns out to lytic cycle by environmental stiimuli or stress conditions.

d.Hypothesis on the origin of viruses

1. The Progressive Hypothesis : It states that the virus particles are originated from mobile genetic elements such as retrotransposons through a progrssive process. The only difference between the retroviruses and retrotransposons are the possession of capsid protein and envelpes(in some) by retroviruses
2. The Regressive Hypothesis: It states that virus are originated through a reductive process from cellular organisms. The virus groups which best supports this hypothesis is nucleocytoplasmic large DNA viruses which include pox virus and Mimivirus
3. The Virus-First Hypothesis: It states that virus was once a self replicating entity and from which other organisms are evolved. It claims that virus was the first organisms on the earth and with the arrival of cellular forms the virus losses its self replicating entity and thrive to survive in living cell as a parasite.

e. Viruses cause large amount of lethal diseases in humans. It also remains as the major organisms that pose periodic pandemic threats to manking in Earth. The following virus possess a greater risk to humans in the present days

1. Ebola virus
2. Human Immunodifficiency virus
3. Herpes Virus
4. SARS-nCOV-19
5. Influenza virus

Currently, as their are no medicine to treat this lethal disease causing viruses, the humans are struggling to stand against this organisms. Due to their highly mutagenic nature, the virus complicates the drug discovey process especially in case of HIV infection. And since it takes atleast 2 years for developing a drug, this viruses cause enough damage to mankind before the drug comes to the market.

f. viruse are one of the most diverse organisms in earth. It has both RNA and DNA as their genetic material and the genetic material may be single stranded or double stranded.

Genome	Virus
Single stranded DNA	Parvovirus
Double stranded DNA	Adenovirus, Pox virus
Single stranded RNA	HIV
Double stranded RNA	Rotavirus

This differences in the genome reflects it in host range.