CH 5 Test Review

Question 1

Sizes of Viruses

Answer 1

Viruses range from 20 nm to 300 nm in size.
Some of the largest viruses (e.g., Mimivirus) can reach 450 nm.

An electron microscope is required to view viruses as they are smaller than most bacteria.

Question 2

Structure of Viruses

Answer 2

Capsid: Protein coat protecting viral genetic material.

Types: Helical, Icosahedral, or Complex.
Nucleic Acid: DNA or RNA, carrying genetic instructions for replication.

Envelope (in some viruses):
Lipid bilayer derived from the host cell membrane.

Contains glycoproteins for cell entry and immune evasion.

Question 3

Characteristics of Envelopes

Answer 3

Composition: Lipids, proteins, and sometimes glycoproteins.

Function: Helps the virus enter host cells and avoid immune responses.

Sensitivity: More fragile than non-enveloped viruses, sensitive to heat, detergent, and alcohol.

Question 4

Nucleic Acid Release

Answer 4

Endocytosis: The virus enters the host by fusing with the host membrane or through receptor-mediated endocytosis.

Membrane Fusion: Enveloped viruses fuse with the host membrane, releasing nucleic acid into the cell.

Direct Injection: Some viruses inject nucleic acid directly into the host cell.

Question 5

Lysogeny

Answer 5

The viral genome integrates into the host’s DNA as a prophage.

The phage remains dormant and replicates with the host until triggered to enter the lytic cycle.

Question 5

Reactivating Viruses

Answer 5

Latency: Some viruses (e.g., herpesviruses) remain dormant in the host and can reactivate later.

Triggers: Stress, immune suppression, or environmental factors can cause reactivation.

Question 6

Bacteriophages

Answer 6

Bacteriophage- “bacteria-eating”, viruses that infect bacteria

Most contain double-stranded DNA, but some RNA exists as well

Every bacterial species is parasitized by various specific bacteriophages 24

Question 7

Viroids

Answer 7

Small, circular RNA molecules that infect plants.

No protein coat and smaller than viruses.

Cause diseases in plants, leading to crop damage.

Question 7

Prions

Answer 7

Infectious, misfolded proteins without nucleic acids.

Cause neurodegenerative diseases like mad cow disease and Creutzfeldt-Jakob disease.
Misfolded prions induce other proteins to misfold similarly.

Question 8

Antiviral Drugs – What They Do

Answer 8

Treat viral infections by targeting specific stages of the virus lifecycle.

Types of Antiviral Drugs:
Entry Inhibitors: Block virus from entering the host cell.

Replication Inhibitors: Block viral genome replication (e.g., reverse transcriptase inhibitors for HIV).

Protease Inhibitors: Block viral protein processing (e.g., HIV protease inhibitors).
Neuraminidase Inhibitors: Prevent influenza virus release (e.g., Tamiflu).