MICR 271 - Module 2
True or false: An increase in genome complexity results in an increase in structural and metabolic
complexity. - True! More complex organisms have more complex, and usually larger, genomes.
What are the stages of bacteriophage assembly? - 1. Infection: Phage attaches itself to bacterial surface
and injects its genetic material into the cell.
2. Replication of genetic material: Virus uses the host cell's machinery to replicate its genetic material.
3. Production of viral proteins: Host cell machinery produces proteins encoded by replicated genetic
material (including for phage structure and lysis proteins)
4. Phage completion: Phages assembled.
5. Lysis of bacterium: Lysis proteins lyse the cell's membrane and allow for phages to exit the cell.
Why are viruses considered to be obligate intracellular parasites? - Viruses can't replicate on their own,
and need to invade a host cell in order to use their machinery to replicate.
What is the structural difference between a non-enveloped virus and an enveloped virus? - Non-
enveloped: Only capsid and nucleic acid.
Enveloped: Surrounded by a lipid membrane with spikes (viral proteins produced by host cell
machinery).
What is included in a non-enveloped virus and what are it's possible shapes? - Composed of a protein
capsid and a nucleic acid (DNA or RNA)
Shapes: Icosahedral or helical
What are the different components of a tailed phage? - Phage head, tail, tail fibre. Contains nucleic
acids.
What is the purpose of the tail on a tailed phage? - The tail facilitates nucleic acid injection into bacteria.
, What is particular about the P22 phage? - The P22 phage lost its tail in evolutionary time. It infects
salmonella.
What is particular about the M13 phage? - It has ~2700 copies of the GP8 protein. It infects E-coli.
What is the difference between lytic and lysogenic infection? - Lytic cycle: Lysis proteins disintegrate
host cell membrane after viral replication.
Lysogenic cycle: Incorporates viral DNA into the host cell's genetic material. This allows viral replication
within the cell. Lysogenic cycles can lead to lytic cycles.
Is a viral RNA strand more likely to stay dormant in a lytic or in a lysogenic cycle? - Lysogenic. It is
protected by the nucleus and the DNA sections are less likely to be read than if it were to be loose in the
cytosol.
True or false: Capsids are stronger on enveloped viruses. - False. The protein capsid on the non-
enveloped viruses are strong and adapted to survive harsh conditions. They do not have the added
protection of a membrane.
What are the steps of non-enveloped virus replication? - 1. Adsorption and endocytosis into host cell.
2. Capsid destruction and viral genome release.
3. Replication and transcription into mRNA
4. Viral proteins are modified and assembled to form new viral particles (ER and Golgi apparatus)
5. Progeny virus released from cell.
What are the steps of enveloped virus replication? An example of this can be seen with HIV. Practice
with a drawing. - 1. Attachment: Viral proteins (gp41 and gp120) attach themselves to immune surface
membranes (CD4).
2. Uncoating: The virus membrane fuses with the host cell's membrane. The capsid disintegrates to
release RNA and reverse transcriptase.
3. Genome replication: Reverse transcription occurs to make RNA into DNA. The viral DNA enters the
cell's nucleus and is integrated into the cell's DNA sequence by integrase. It is then transcribed into
mRNA with the rest of the DNA sequence.
True or false: An increase in genome complexity results in an increase in structural and metabolic
complexity. - True! More complex organisms have more complex, and usually larger, genomes.
What are the stages of bacteriophage assembly? - 1. Infection: Phage attaches itself to bacterial surface
and injects its genetic material into the cell.
2. Replication of genetic material: Virus uses the host cell's machinery to replicate its genetic material.
3. Production of viral proteins: Host cell machinery produces proteins encoded by replicated genetic
material (including for phage structure and lysis proteins)
4. Phage completion: Phages assembled.
5. Lysis of bacterium: Lysis proteins lyse the cell's membrane and allow for phages to exit the cell.
Why are viruses considered to be obligate intracellular parasites? - Viruses can't replicate on their own,
and need to invade a host cell in order to use their machinery to replicate.
What is the structural difference between a non-enveloped virus and an enveloped virus? - Non-
enveloped: Only capsid and nucleic acid.
Enveloped: Surrounded by a lipid membrane with spikes (viral proteins produced by host cell
machinery).
What is included in a non-enveloped virus and what are it's possible shapes? - Composed of a protein
capsid and a nucleic acid (DNA or RNA)
Shapes: Icosahedral or helical
What are the different components of a tailed phage? - Phage head, tail, tail fibre. Contains nucleic
acids.
What is the purpose of the tail on a tailed phage? - The tail facilitates nucleic acid injection into bacteria.
, What is particular about the P22 phage? - The P22 phage lost its tail in evolutionary time. It infects
salmonella.
What is particular about the M13 phage? - It has ~2700 copies of the GP8 protein. It infects E-coli.
What is the difference between lytic and lysogenic infection? - Lytic cycle: Lysis proteins disintegrate
host cell membrane after viral replication.
Lysogenic cycle: Incorporates viral DNA into the host cell's genetic material. This allows viral replication
within the cell. Lysogenic cycles can lead to lytic cycles.
Is a viral RNA strand more likely to stay dormant in a lytic or in a lysogenic cycle? - Lysogenic. It is
protected by the nucleus and the DNA sections are less likely to be read than if it were to be loose in the
cytosol.
True or false: Capsids are stronger on enveloped viruses. - False. The protein capsid on the non-
enveloped viruses are strong and adapted to survive harsh conditions. They do not have the added
protection of a membrane.
What are the steps of non-enveloped virus replication? - 1. Adsorption and endocytosis into host cell.
2. Capsid destruction and viral genome release.
3. Replication and transcription into mRNA
4. Viral proteins are modified and assembled to form new viral particles (ER and Golgi apparatus)
5. Progeny virus released from cell.
What are the steps of enveloped virus replication? An example of this can be seen with HIV. Practice
with a drawing. - 1. Attachment: Viral proteins (gp41 and gp120) attach themselves to immune surface
membranes (CD4).
2. Uncoating: The virus membrane fuses with the host cell's membrane. The capsid disintegrates to
release RNA and reverse transcriptase.
3. Genome replication: Reverse transcription occurs to make RNA into DNA. The viral DNA enters the
cell's nucleus and is integrated into the cell's DNA sequence by integrase. It is then transcribed into
mRNA with the rest of the DNA sequence.
