Virology Final Part 1 Flashcards
What is the definition of a virus?
Chemical complexes of RNA or DNA protected by protein
What do viruses lack so that they cannot synthesize their own proteins?
- cannot extract energy from molecules to build nucleic acids and proteins
- no instructions to make nucleotides and amino acids
- no ribosomes
What makes up a capsid?
Proteins
Where is the gene that encodes the protein structure for the capsomere?
The virus’ genome
What is a capsid made up of?
Capsomeres (protein subunits)
What is an envelope made out of?
Lipid bilayer + glycoproteins imbedded, and sometimes a matrix layer of proteins just below the envelope
Where does the envelope structure come from?
Stolen from the host cell
Which kind of virus is more fragile in the environment?
Enveloped
What are the two general pathways of virus evolution?
Co-evolution with host, and infection of multiple host species
What is the advantage/disadvantage of co-evolution with the host, and what is an example of it?
- If the host does well, so does the virus, but if the host goes extinct, so does the virus
- smallpox
What is the advantage/disadvantage of infecting with multiple host species, and what is an example of it?
- if one host species is compromised, the virus can replicate in another, but it cannot optimize for any one situation
- influenza, rabies
What are the five steps of virus replication?
- Virus adsorption/ attachment to host cell
- Genome (and any needed proteins) enter the cell
- Gene expression (Making the parts): Synthesis of viral mRNA, viral proteins, replication of genome
- Assembly of virus from parts
- Release from host cell
What additional layers can viruses have?
- lipid bilayer envelope at the surface
- layer of protein between capsid and envelope
- internal lipid layers
- protein occlusion bodies
What are the functions of a capsid?
- Protect the chemically labeled virus genome from nucleases, from agents, and from mechanical forces
- Delivery of the virus’ genome to the location within the cell where the genome can be replicated and expressed
How does the virus and host interact with each other?
Host cell: virus receptor (Normal cell structure made out of protein or carb+protein that the virus exploits)
Virus: anti-receptor
What are a virus’ possible methods of entering the genome into the cell?
- 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
What causes a capsid to change from a stable structure to an unstable structure?
- interactions with other proteins
- changes in pH
- cleavage of proteins
- unfolding of proteins
What is adsorption?
random weak collisions that lead to the attachment of the virus
particle to the virus receptor
What is virus attachment?
multiple molecular interactions that lead to a firm binding so
that the virus’ genome can enter the cell
What does it mean if a virus is both susceptible and permissive?
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)
What direction do polymerase read templates? What direction do they synthesize the complementary strand?
3’-5’ ; 5’-3’
What direction do ribosomes read the mRNA template? What direction do they synthesize polypeptide?
5’-3’; N to C
Why do some viruses package their own replicate every enzymes in their capsids?
- 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
- RNA viruses: cell’s RNA pol can’t read an RNA template
What is something that ALL RNA viruses must have in their genome?
A gene that encodes a polymerase that can read RNA as a template and synthesize RNA or DNA
If a DNA virus is replicating/expressing its genome in the nucleus, what polymerase does it use?
The cell’s DNA or RNA polymerase
If a DNA virus is replicating/expressing its genome in the CYTOPLASM, what options does it have for polymerases?
- genome encodes the DNA or RNA polymerase
- capsids contains pre-made RNA/DNA polymerase
If an RNA virus is replicating/expressing its genome in the nucleus, where does it get its polymerases?
The genome encodes an RNA polymerase, and the capsid may contain a pre-made one
If an RNA virus is replicating/expressing its genome in the cytoplasm, where does it get its polymerases?
- genome encodes it (RDRP)
- positive sense: synthesize after infection
- negative sense: must have it packaged in the capsid
What is the process of a retrovirus?
RNA—ssDNA—dsDNA—integrate—RNA
What does postive sense RNA need for a host cell ribosome to translate it?
5’ cap, start codon, single ORF, stop codon, polyA tail
How do viruses break up poly proteins that are translated on ribosomes?
Self-proteolytic cleavage: Folds the protease and it becomes active when the protein folds
- protease cuts them
