Virology Final Part 1

Question 1

What is the definition of a virus?

Answer 1

Chemical complexes of RNA or DNA protected by protein

Question 2

What do viruses lack so that they cannot synthesize their own proteins?

Answer 2

• cannot extract energy from molecules to build nucleic acids and proteins
• no instructions to make nucleotides and amino acids
• no ribosomes

Question 3

What makes up a capsid?

Answer 3

Proteins

Question 4

Where is the gene that encodes the protein structure for the capsomere?

Answer 4

The virus’ genome

Question 5

What is a capsid made up of?

Answer 5

Capsomeres (protein subunits)

Question 6

What is an envelope made out of?

Answer 6

Lipid bilayer + glycoproteins imbedded, and sometimes a matrix layer of proteins just below the envelope

Question 7

Where does the envelope structure come from?

Answer 7

Stolen from the host cell

Question 8

Which kind of virus is more fragile in the environment?

Answer 8

Enveloped

Question 9

What are the two general pathways of virus evolution?

Answer 9

Co-evolution with host, and infection of multiple host species

Question 10

What is the advantage/disadvantage of co-evolution with the host, and what is an example of it?

Answer 10

• If the host does well, so does the virus, but if the host goes extinct, so does the virus
• smallpox

Question 11

What is the advantage/disadvantage of infecting with multiple host species, and what is an example of it?

Answer 11

• if one host species is compromised, the virus can replicate in another, but it cannot optimize for any one situation
• influenza, rabies

Question 12

What are the five steps of virus replication?

Answer 12

1. Virus adsorption/ attachment to host cell
2. Genome (and any needed proteins) enter the cell
3. Gene expression (Making the parts): Synthesis of viral mRNA, viral proteins, replication of genome
4. Assembly of virus from parts
5. Release from host cell

Question 13

What additional layers can viruses have?

Answer 13

• lipid bilayer envelope at the surface
• layer of protein between capsid and envelope
• internal lipid layers
• protein occlusion bodies

Question 14

What are the functions of a capsid?

Answer 14

1. Protect the chemically labeled virus genome from nucleases, from agents, and from mechanical forces
2. Delivery of the virus’ genome to the location within the cell where the genome can be replicated and expressed

Question 15

How does the virus and host interact with each other?

Answer 15

Host cell: virus receptor (Normal cell structure made out of protein or carb+protein that the virus exploits)
Virus: anti-receptor

Question 16

What are a virus’ possible methods of entering the genome into the cell?

Answer 16

• just the genome goes into the cell
• the virus enters the cell in an endosome and the genome is released into the cytoplasm or nucleus
• the virus envelope fuses to the cell membrane, and releases the genome into the cytoplasm or nucleus

Question 17

What causes a capsid to change from a stable structure to an unstable structure?

Answer 17

• interactions with other proteins
• changes in pH
• cleavage of proteins
• unfolding of proteins

Question 18

What is adsorption?

Answer 18

random weak collisions that lead to the attachment of the virus
particle to the virus receptor

Question 19

What is virus attachment?

Answer 19

multiple molecular interactions that lead to a firm binding so
that the virus’ genome can enter the cell

Question 20

What does it mean if a virus is both susceptible and permissive?

Answer 20

Susceptible: ability for virus to get genome into the host cell (structure)
Permissive: ability of the virus to replicate its genome in the host cell (presence of enzyme, expression linked to cell cycle)

Question 21

What direction do polymerase read templates? What direction do they synthesize the complementary strand?

Answer 21

3’-5’ ; 5’-3’

Question 22

What direction do ribosomes read the mRNA template? What direction do they synthesize polypeptide?

Answer 22

5’-3’; N to C

Question 23

Why do some viruses package their own replicate every enzymes in their capsids?

Answer 23

1. Some species of viruses replicate their genomes in the cytoplasm of the cell and they can’t use cellular DNA/RNA pol’s in the nucleus to make the enzymes
2. RNA viruses: cell’s RNA pol can’t read an RNA template

Question 24

What is something that ALL RNA viruses must have in their genome?

Answer 24

A gene that encodes a polymerase that can read RNA as a template and synthesize RNA or DNA

Question 25

If a DNA virus is replicating/expressing its genome in the nucleus, what polymerase does it use?

Answer 25

The cell’s DNA or RNA polymerase

Question 26

If a DNA virus is replicating/expressing its genome in the CYTOPLASM, what options does it have for polymerases?

Answer 26

• genome encodes the DNA or RNA polymerase

- capsids contains pre-made RNA/DNA polymerase

Question 27

If an RNA virus is replicating/expressing its genome in the nucleus, where does it get its polymerases?

Answer 27

The genome encodes an RNA polymerase, and the capsid may contain a pre-made one

Question 28

If an RNA virus is replicating/expressing its genome in the cytoplasm, where does it get its polymerases?

Answer 28

• genome encodes it (RDRP)
• positive sense: synthesize after infection
• negative sense: must have it packaged in the capsid

Question 29

What is the process of a retrovirus?

Answer 29

RNA—ssDNA—dsDNA—integrate—RNA

Question 30

What does postive sense RNA need for a host cell ribosome to translate it?

Answer 30

5’ cap, start codon, single ORF, stop codon, polyA tail

Question 31

How do viruses break up poly proteins that are translated on ribosomes?

Answer 31

Self-proteolytic cleavage: Folds the protease and it becomes active when the protein folds
- protease cuts them