Viruses Practice Questions

Correct answer: Protein capsid

Every virus consists of a nucleic acid genome protected by a protein coat known as a capsid. Viroids (infectious RNA lacking a capsid) are not classified as true viruses, and features like glycoprotein spikes and reverse transcriptase are present only in certain viral families, not in all viruses.

Correct answer: Capsomeres

Capsomeres are the individual protein building blocks that spontaneously self-assemble to create the geometric structure of the capsid. Their arrangement determines whether the virus is helical, polyhedral, or complex in shape.

Correct answer: Reverse transcriptase

Reverse transcriptase is an enzyme that catalyzes the transcription of retroviral RNA into DNA. This process reverses the standard 'central dogma' of molecular biology, where DNA is typically transcribed into RNA.

Correct answer: Lysogenic cycle

In the lysogenic cycle, the viral DNA (prophage) is incorporated into the host genome and replicated along with it. This allows the virus to persist in a latent state until environmental triggers induce the lytic cycle.

Correct answer: Binding to sialic acid receptors

Hemagglutinin is a surface glycoprotein that recognizes and binds to sialic acid receptors on the host's epithelial cells. This binding is the critical first step required for the virus to enter the respiratory tract cells.

Correct answer: An intact extracellular virus particle

A virion is the fully assembled, extracellular form of a virus. It consists of the nucleic acid core and the protein capsid (and envelope, if present) and is capable of initiating an infection in a new host.

Correct answer: They can only replicate inside a host cell

Viruses lack ribosomes, metabolic enzymes, and the machinery for protein synthesis. Consequently, they must hijack the biochemical resources of a host cell to produce new viral components and replicate.

Correct answer: No infectious virions exist inside or outside the cell

During the eclipse period, the virus has uncoated and is busy synthesizing its components; therefore, no fully assembled, infectious virions are present. This period ends once the first new virions are assembled and become detectable.

Correct answer: Negative-sense single-stranded RNA (-ssRNA)

Negative-sense RNA is complementary to mRNA and cannot be directly translated by host ribosomes. These viruses must carry their own RNA-dependent RNA polymerase to transcribe the negative strand into a positive mRNA strand upon entry.

Correct answer: Consist only of misfolded protein

Prions are unique infectious particles composed solely of protein (PrPSc). Unlike viruses, they contain no DNA or RNA and cause disease by inducing normal host proteins to misfold into the pathogenic form.

Correct answer: Budding

Budding allows enveloped viruses to exit the host cell without causing immediate cell death. The virus acquires its lipid envelope from the host's membrane, which has been modified with viral-specific proteins.

Correct answer: Herpes Simplex (HSV)

Herpes viruses are classic examples of latency, where the viral genome remains dormant in nerve ganglia for years. Periodically, the virus can reactivate and cause recurrent symptoms like cold sores.

Correct answer: Method of mRNA synthesis and genome type

Created by David Baltimore, this system groups viruses into seven classes based on the nature of their genome (DNA vs RNA, single vs double stranded) and the pathway they use to produce mRNA.

Correct answer: The lipid envelope

The lipid envelope is highly susceptible to chemical disinfectants because these agents dissolve lipids. Once the envelope is disrupted, the virus loses its attachment proteins and its ability to infect cells, which is why handwashing is effective against enveloped viruses like SARS-CoV-2.

Correct answer: Abrupt reassortment of viral genome segments

Antigenic shift occurs when two different influenza strains infect the same cell and swap genome segments. This results in a major change in surface antigens, often leading to pandemics because the population has no pre-existing immunity.

Correct answer: A small, naked RNA that infects plant cells

Viroids are even simpler than viruses, consisting only of short strands of circular, catalytic RNA without a protein coat. They are significant pathogens in the agricultural industry, causing diseases in crops like potatoes and citrus.

Correct answer: Viral Tropism

Tissue tropism refers to the specificity of a virus for particular cells or organs, which is determined by the presence of specific receptors on the host cell surface that match the virus's attachment proteins.

Correct answer: Adsorption

Adsorption is the physical binding of the viral surface proteins to specific receptor molecules on the host cell membrane. This 'lock and key' interaction must occur before the virus can penetrate the cell.

Correct answer: Human Papillomavirus (HPV)

Certain high-risk strains of HPV are oncogenic; they can integrate their DNA into the host's genome and produce proteins that interfere with tumor suppressor genes, leading to uncontrolled cell growth and cancer.

Correct answer: The release of the viral genome from its capsid

Uncoating is the removal of the protein capsid after the virus has entered the host cell. This step releases the viral genome into the cytoplasm or nucleus so that replication and transcription can begin.