16 Questions
What is a characteristic of viruses?
They require host cells for replication
What is the composition of a virus?
Nucleic acid and protein
Why are viruses so small?
Because they can only carry a few genes
What is the purpose of receptors on the surface of host cells?
To allow the virus to enter the cell
How do antiviral drugs work?
By binding to and blocking viral receptors
What is the mechanism of viral entry?
It varies depending on the type of virus
What happens once the virus is inside the host cell?
The virus begins the cycle of replication
Why do viruses only cause specific infections?
Because they rely on other cells for metabolic functions
What is the reason why some viruses have additional steps in their replication process?
Because host cells have DNA genomes and don't carry the necessary enzymes for replication of RNA
What is the first step in the replication process of a virus?
Attachment
What is the phase of replication where the virus takes over the host cell's machinery?
Nucleic acid and protein synthesis
Why can't antiviral drugs target the host cell enzymes used by viruses for replication?
Because the host cell enzymes are also required by the host cell
What is the basis of the nucleoside analogs used to treat diseases such as HIV?
The virus's polymerase
What is the reason why antiviral drugs cannot kill viruses?
Because viruses are not living things
What is the last step in the replication process of a virus?
Release
What is the phase of replication where the virus's proteins and nucleic acids are packaged into new virions?
Assembly and packaging
Study Notes
Characteristics of Viruses
- Not true living cells
- Do not take in nutrients or expel wastes
- Require host cells for replication
- No metabolic activities
- Consist of only nucleic acid (either DNA or RNA) and protein
- May be enclosed in a lipid and protein envelope
- Very small, require an electron microscope to be viewed
- Can only carry a few genes
Viral Infection and Replication
- Viruses rely on host cells for metabolic functions
- Need to enter host cells and take over cellular machinery
- Recognize specific molecules on cell surface to bind and gain entry
- Use receptors to enter cells (e.g. sialic acid for influenza virus)
- Antiviral drugs work by binding to and blocking viral receptors
- Mechanism of viral entry varies depending on whether the virus has an envelope
Steps in Viral Replication
- Attachment to a susceptible host cell
- Penetration of either the whole virus or just its nucleic acid into the cell
- Nucleic acid and protein synthesis (virus takes over host cell machinery)
- Assembly and packaging of proteins and nucleic acids into new virions
- Release of mature virions from the host cell
Antiviral Drugs
- Work by intervening in the viral replication process
- Target specific stages of replication (e.g. attachment, penetration, synthesis)
- Nucleoside analogs used to treat diseases like HIV target the viral polymerase enzyme
Learn about the fundamental characteristics of viruses, including their structure and replication process. Understand how viruses interact with host cells and rely on them for metabolic functions.
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