AP-Micro Virology: Structure, Replication, and Diagnosis 2 — Questions and Answers
Question 1: The eclipse period in the viral replication cycle is defined as the time when:
- Infectious virions cannot be detected inside or outside the infected cell (Correct answer)
- The cell undergoes lysis releasing mature virions
- Viral DNA integrates into the host chromosome
- The burst size reaches its maximum
Correct answer: Infectious virions cannot be detected inside or outside the infected cell
During the eclipse period the virus has uncoated and been disassembled, so no intact infectious particles are detectable until new assembly begins.
Question 2: In lysogenic viral infection, the integrated viral genome within the host chromosome is called a:
- Virion
- Prophage (provirus) (Correct answer)
- Capsid
- Replicon
Correct answer: Prophage (provirus)
The integrated viral genome in a lysogenic cell is called a prophage (for bacteriophages) or provirus (for animal viruses), replicating silently with the host.
Question 3: During which step of viral replication are viral nucleic acids and proteins synthesized using host machinery?
- Adsorption
- Penetration
- Biosynthesis (Correct answer)
- Assembly
Correct answer: Biosynthesis
Biosynthesis is the phase in which viral genomes are replicated and viral mRNAs are transcribed and translated into structural and nonstructural proteins.
Question 4: Cytopathic effects (CPE) observed in viral cell cultures include all of the following EXCEPT:
- Cell rounding and detachment
- Syncytia (multinucleated giant cell) formation
- Intranuclear or intracytoplasmic inclusion bodies
- Increased host cell proliferation (hyperplasia) (Correct answer)
Correct answer: Increased host cell proliferation (hyperplasia)
CPE represents cytodestructive changes caused by viral infection; uncontrolled proliferation is not a feature of CPE, though some oncogenic viruses can transform cells.
Question 5: Enveloped viruses acquire their lipid membrane during release by:
- Explosive lysis of the host cell
- Budding through the host cell membrane, incorporating host lipids and viral glycoproteins (Correct answer)
- Secretion via lysosomes
- Assembly in the endoplasmic reticulum only
Correct answer: Budding through the host cell membrane, incorporating host lipids and viral glycoproteins
During budding, enveloped viruses incorporate viral glycoproteins into a patch of host cell membrane and pinch off as enveloped virions without lysing the cell.
Question 6: HIV requires CD4 as its primary receptor plus which co-receptor(s) for fusion and cell entry?
- CXCR4 or CCR5 (Correct answer)
- CD8 molecule
- Sialic acid residues
- CD21 complement receptor
Correct answer: CXCR4 or CCR5
HIV uses CD4 for initial binding and either CXCR4 (T-cell tropic strains) or CCR5 (macrophage-tropic strains) as an obligatory co-receptor for membrane fusion.
AP-Micro Virology: Structure, Replication, and Diagnosis 2
The eclipse period in the viral replication cycle is defined as the time when: