Question

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: In a cell culture, the concentration of DI (Defective Interfering) particles increases greatly with the serial passage at high multiplicity
Reason R: Their shortened genomes require less time to be replicated
In light of the above statements, choose the correct answer from the options given below:

• A. Both A and R are true and R is the correct explanation of A
• B. Both A and R are true but R is NOT the correct explanation of A
• C. A is true but R is false
• D. A is false but R is true

Hint:

DI particles are genomic deletion mutants that replicate faster because of their smaller size, outcompeting full-length helper viruses during co-infection at high MOI.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Defective Interfering (DI) particles are subgenomic viral deletion mutants that cannot replicate independently because they lack essential viral genes.
However, they can replicate when co-infecting a cell with a complete, functional "helper" wild-type virus that provides the missing proteins.
Detailed Explanation:
Let us analyze both statements:
- Assertion A: In cell culture, DI particles accumulate rapidly during serial passage at high Multiplicity of Infection (MOI). High MOI ensures that almost every host cell is infected by multiple viral particles, increasing the probability that a DI particle and a wild-type helper virus will co-infect the same cell. Under these conditions, DI particles can replicate and accumulate. At low MOI, co-infection is rare, and DI particles cannot replicate. Thus, Assertion A is true.
- Reason R: Because DI particles contain large deletions in their genomes, their genetic material is much shorter than that of the wild-type virus. As a result, their replication takes less time. During co-infection, the replication machinery of the host and virus replicates the shorter DI genomes faster than the full-length wild-type genomes, allowing the DI genomes to outcompete and deplete the replication machinery. This explains why they interfere with wild-type replication and accumulate rapidly during co-infection. Thus, Reason R is true and provides the direct biochemical explanation for Assertion A.

Step 2: Final Answer:
Both A and R are true, and R is the correct explanation of A.