Viruses Flashcards
Features all viruses share
- No cytoplasm
- Few or no enzymes
- Small in size (20-300nm)
- Has nucleic acid as genetic material
- Has a caspid
How do viruses vary?
- Size range
- Whether they use DNA or RNA
- Single or double stranded
- Circular or linear genome
- Proteins in and shape of capsid
- Size of genome
- Presence of a lipid envelope
- Genes present
What determines whether a virus replicates through lytic cycle or lysogenic cycle?
Viruses with a lipid envelope use the lysogenic cycle and ones without use the lytic cycle
7 Stages of lytic cycle
- Phage attaches to host cell
- Phage DNA entry into host cell
- Phage DNA replication
- Phage protein synthesis
- Assembly of new phage viruses
- Lysis
- Spread
5 stages of lysogenic cycle
- Phage attaches to host cell
- Phage DNA entry into host cell
- Phage DNA is integrated into host genome
- DNA replication
- Cell division
What is the virus first hypothesis and what evidence is there against it?
The theory that viruses existed in a precellular world as self replicating units
EVIDENCE AGAINST:
Viruses are intracellular parasites (need a cell to replicate) so they couldn’t have existed without cells.
Viruses use the same genetic code as other cells, so it is likely they have evolved from them.
Why do scientists beleive that viruses evolved from cells? (3 points)
- Share the same genetic code
- Require cells to replicate
- Viruses share more protein folds in common with cells than each other
Progressive vs Regressive virus hypothesis
Progressive states that viruses came from taking and modifying cell components
Regressive states that viruses come from cells which have lost their cellular components.
What are the sub-sections in terms of shape of virus DNA?
Can be linear or circular, and inside those categories they can either be single or double stranded
What are the sub-sections in terms of shape of virus RNA?
Can be linear or circular, and inside those categories they can either be single or double stranded - HOWEVER a circular double stranded RNA does not exist
Why is there such rapid evoloution in viruses?
- Evoloutionary change happens over generations, and viruses have short generation times
- Mutation rates are high - more genetic variation
- High amounts of natural selection since host organism has mechansim to destroy viruses
What is phage induction?
When a prophage (Forms when phage DNA is integrated into host genome) in a bacteria is exposed to stressors (low nutrient conditions, UV light), it extracts itself from the genome and carries out lysis instead
