Ch 17 Flashcards
What is a capsid?
protein coat that encloses a viral genome.
Define capsomeres
Protein subunits that compose viral capsids.
What is a viral envelope?
membrane derived from host cells that surrounds some viral capsids.
What is the host range of a virus?
The limited number of species a virus can infect.
What is a prophage?
Viral DNA integrated into a host bacterial genome during lysogeny.
What is reverse transcriptase?
An enzyme that transcribes RNA into DNA in retroviruses.
What is a provirus?
Viral DNA integrated into a host cell’s genome in retroviruses.
What are bacteriophages?
Viruses that infect bacteria.
What is the lytic cycle?
viral replication cycle that results in the death of the host cell.
What is the lysogenic cycle?
viral replication cycle where the virus coexists with its host.
T/F: All viruses have double-stranded DNA genomes.
False. Viruses can have single-stranded or double-stranded DNA or RNA genomes.
T/F: Viruses can replicate outside of host cells.
False. Viruses are obligate intracellular parasites and can only replicate within host cells.
T/F: The viral envelope is made of proteins produced by the virus.
False. The viral envelope is derived from host cell membranes
T/F: Bacteriophages infect animal cells.
False. Bacteriophages specifically infect bacteria.
T/F: HIV is a retrovirus.
T
T/F: All viruses use the lytic cycle for replication.
False. Some viruses use the lysogenic cycle or can alternate between lytic and lysogenic cycles.
T/F: Viral genomes always consist of a single molecule.
False. While viral genomes are usually a single molecule, they may consist of multiple molecules.
T/F: The lysogenic cycle always results in immediate host cell death.
False. The lysogenic cycle allows for coexistence of the virus and host.
T/F: Enveloped viruses enter host cells through fusion with the cell membrane.
T
T/F: HIV directly kills T cells upon infection.
False. HIV integrates into the host genome and may not immediately kill the cell.
Viruses consist of a nucleic acid genome enclosed in a protein coat called a ________.
capsid
The first step of viral replication involves the virus ________ to the host cell.
attaching
Viruses that can switch between lytic and lysogenic cycles are called ________ phages.
temperate
In HIV, the enzyme ________ ________ transcribes the RNA genome into double-stranded DNA.
reverse transcriptase
The ________ cycle of bacteriophages results in the death of the host cell
lytic
Viral proteins that bind to receptor molecules on host cells are located on the ________ or envelope.
capsid
A virus integrated into the host genome during lysogeny is called a ________.
prophage
HIV is classified as a ________ because it transcribes its RNA into DNA before integration.
retrovirus
The protein subunits that make up viral capsids are called ________.
capsomeres
Viruses can only infect a limited number of species, which is known as their ________ ________.
host range
Which of the following is NOT a possible viral genome type?
a) Single-stranded DNA
b) Double-stranded RNA
c) Triple-stranded DNA
d) Single-stranded RNA
c) Triple-stranded DNA
How many phage particles are typically released at the end of a lytic cycle?
a) 10-20
b) 50-100
c) 100-200
d) 500-1000
c) 100-200
What is the approximate time for a complete lytic cycle at 37°C?
a) 5-10 minutes
b) 20-30 minutes
c) 1-2 hours
d) 4-6 hours
b) 20-30 minutes
Which of the following is NOT a step in the basic viral replication cycle?
a) Attachment
b) Entry
c) Photosynthesis
d) Assembly
c) Photosynthesis
What percentage of human cancers are related to viral infections?
a) Less than 5%
b) Above 15%
c) Exactly 10%
d) 50-60%
b) Above 15%
Which of the following is a characteristic of retroviruses?
a) They have a DNA genome
b) They directly kill host cells upon entry
c) They integrate their genetic material into the host genome
d) They cannot infect human cells
c) They integrate their genetic material into the host genome
What type of virus is HIV?
a) DNA virus
b) Bacteriophage
c) Retrovirus
d) Plant virus
c) Retrovirus
Which environmental factor can induce a prophage to enter the lytic cycle?
a) Low temperature
b) High-energy radiation (UV)
c) Increased nutrients
d) Decreased oxygen levels
b) High-energy radiation (UV)
How many copies of its RNA genome does HIV package into each virion?
a) One
b) Two
c) Three
d) Four
b) Two
What is the primary target cell type for HIV infection?
a) Red blood cells
b) Liver cells
c) T cells
d) Skin cells
c) T cells
