QUIZ 2 - BI234 EXAM QUESTIONS AND ANSWERS WITH COMPLETE
SOLUTIONS
Parts of a virion - parts of all - no virus can be a virus without:
1. nucleic acid - most important - genome
2. capsid (shell)
-capsomere proteins make up the capsid. (self assembling)
3. spike proteins - false ligands for cell surface receptors - pretend to be ligands
Other virion parts that some have:
1. envelope: lipid membrane stolen from a cell
-prevents desiccation
-acts as camouflage
2. matrix proteins: big protein shell
3. enzymes waiting to be active in a new host cell
Nucleic acid
Just like a cell's genome, it encodes all protein sequences and all instructions for
controlling which proteins get made at which time.
Capsid (protein shell) made of capsomere proteins
1. Capsid protects the nucleic acid
2.Capsomeres self-assemble to make the capsid.
Spike proteins
1. Spike proteins are the major factor that attaches to host cells. A typical virus has a
spike protein that mimics a ligand for a cell surface receptor. If the receptor binds the
spike protein (like a typical receptor-ligand interaction) the virus will successfully enter
the host cell. Review what a receptor its ligand are and how they typically interact.
2. Spike proteins are critically important for viral replication. They are the virion’s only
hope of entering a host cell. They absolutely must successfully attach to the cell
surface.
3. Human immune systems can quickly neutralize virions (and thus slow down viral
infections) by targeting spike proteins. What part of the immune system neutralizes
virions?
4.The spike proteins are the most obvious site of the “Evolutionary arms race” between
viruses and their hosts. Explain how antibodies and spike proteins might force each
other to evolve. 1 paragraph
Envelope
The envelope is a lipid bilayer membrane stolen from the host cell.
Functions of the envelope:
a. Prevention of desiccation: Proteins and nucleic acids generally need some water to
maintain their shapes. Envelopes help keep water in.
b. Sometimes, as camouflage: If it was stolen from a host cell membrane, it can contain
all the glycolipids that identified the host cell. In other words, an envelope has molecules
that tell a macrophage “I’m a hepatocyte” or “I’m an epithelial cell” when it is, in fact, a
virion.
c.Assisting in entry into host cells. See the animal virus replication cycle.
Enzymes function
help the virus replicate once it enters a cell
SOLUTIONS
Parts of a virion - parts of all - no virus can be a virus without:
1. nucleic acid - most important - genome
2. capsid (shell)
-capsomere proteins make up the capsid. (self assembling)
3. spike proteins - false ligands for cell surface receptors - pretend to be ligands
Other virion parts that some have:
1. envelope: lipid membrane stolen from a cell
-prevents desiccation
-acts as camouflage
2. matrix proteins: big protein shell
3. enzymes waiting to be active in a new host cell
Nucleic acid
Just like a cell's genome, it encodes all protein sequences and all instructions for
controlling which proteins get made at which time.
Capsid (protein shell) made of capsomere proteins
1. Capsid protects the nucleic acid
2.Capsomeres self-assemble to make the capsid.
Spike proteins
1. Spike proteins are the major factor that attaches to host cells. A typical virus has a
spike protein that mimics a ligand for a cell surface receptor. If the receptor binds the
spike protein (like a typical receptor-ligand interaction) the virus will successfully enter
the host cell. Review what a receptor its ligand are and how they typically interact.
2. Spike proteins are critically important for viral replication. They are the virion’s only
hope of entering a host cell. They absolutely must successfully attach to the cell
surface.
3. Human immune systems can quickly neutralize virions (and thus slow down viral
infections) by targeting spike proteins. What part of the immune system neutralizes
virions?
4.The spike proteins are the most obvious site of the “Evolutionary arms race” between
viruses and their hosts. Explain how antibodies and spike proteins might force each
other to evolve. 1 paragraph
Envelope
The envelope is a lipid bilayer membrane stolen from the host cell.
Functions of the envelope:
a. Prevention of desiccation: Proteins and nucleic acids generally need some water to
maintain their shapes. Envelopes help keep water in.
b. Sometimes, as camouflage: If it was stolen from a host cell membrane, it can contain
all the glycolipids that identified the host cell. In other words, an envelope has molecules
that tell a macrophage “I’m a hepatocyte” or “I’m an epithelial cell” when it is, in fact, a
virion.
c.Assisting in entry into host cells. See the animal virus replication cycle.
Enzymes function
help the virus replicate once it enters a cell
