Question 1: Viruses are acellular particles that infect host cells to reproduce. Describe the basic structure of a virus and explain how it replicates within a host cell.

Answer: Viruses consist of genetic material (DNA or RNA) enclosed in a protein coat called a capsid. Some viruses have an additional lipid envelope. They replicate by attaching to specific receptors on a host cell, injecting their genetic material, and hijacking the host's cellular machinery to produce new virus particles, which are then released to infect other cells.

Question 1: Define a virus and contrast it with bacteria.

Answer: A virus is an acellular particle that infects host cells to reproduce, whereas bacteria are single-celled living organisms that can reproduce independently. Viruses require a host to replicate, while bacteria can grow and divide on their own.

Question 2: Explain why viruses are considered obligate intracellular parasites.

Answer: Viruses are obligate intracellular parasites because they cannot reproduce or carry out metabolic processes outside a host cell; they must infect a host cell to replicate.

Question 1: A viral sample contains 2 x 10^6 infectious units per millilitre. If a scientist has 0.5 millilitres of this sample, how many infectious units are present in total?

Answer: 1 x 10^6 infectious units

Question 2: The replication cycle of a certain virus takes 8 hours. How many cycles will occur in 48 hours assuming continuous replication?

Answer: 6 cycles

Question 1: Design a basic experiment to test the effectiveness of a new antiviral drug against a virus in vitro. Include variables to control, variables to measure, and safety precautions.

Answer: The experiment should include a control group with no drug and a test group with the drug. Variables to control include virus concentration, incubation time, and temperature. The variable to measure is the number of infectious units post-treatment. Safety precautions involve working in a sterile environment, using PPE, and proper disposal of infected materials.

Question 1: A study reports that after exposure to a certain antiviral agent, the number of virus particles in a sample decreased from 5 x 10^8 to 1 x 10^7 over 24 hours. Calculate the fold reduction in virus particles.

Answer: Fold reduction = (Initial count) / (Final count) = (5 x 10^8) / (1 x 10^7) = 50

Question 1: Describe the process by which a virus infects a host cell and reproduces, highlighting key stages.

Answer: A virus attaches to a specific receptor on the host cell surface, then injects or releases its genetic material into the cell. The viral genetic material hijacks the host's cellular machinery to produce viral components. These components are assembled into new virus particles, which are then released from the cell, often destroying it, to infect new cells.

Question 1: Explain how understanding viral replication is important in developing antiviral drugs and vaccines.

Answer: Understanding viral replication helps scientists identify stages in the virus life cycle that can be targeted by drugs or vaccines. For example, vaccines can stimulate immunity before infection, while antiviral drugs can inhibit specific steps like entry, replication, or assembly, reducing the severity of infections.