Chapter 1 - V Flashcards
Virus
chemical complexes of RNA or DNA protected by protein
What are viruses
Viruses are tiny non-living agents
all viruses have genetic information surrounded by a protein coat
some also contain external structure and an envelope pf phospholipids
They are obligate intracellular parasites - require host to reproduce
Each type of virus infects a specific unicellular species or type of cell in multicellular - need the right virus receptor
What are viruses
Viruses are not cells
They cannot synthesize their own ATP, aa, or nucleotides
They cannot synthesize protein on their own
- they lack the ability to extract energy from molecules to build nucleic acids
- they lack ribosomes
- they have an extracellular state (inert) and intracellular state (replicating)
Viruses vs cells
cells are always dsDNA, virus can be DNA or RNA, ss or ds
viruses don’t have plasma membrane (maybe envelope)
Virus can’t carry out translation independently like normal cells. Requires ATP and nucleotide from the host cell
virus also can’t do translation without a host cell
Viruses don’t have metabolic capabilities. Cells have extensive ATP synthesis, oxidation of reduced C. aa and nucleotide biosynthesis
What percentage of your genomes has its origins in virus sequence?
50%
Central dogma of molecular biology
Usually cells DNA –> RNA –> protein
however viruses can mix these steps up eg.
RNA - DNA - RNA - Protein
RNA - RNA - protein
Diversity of viruses
Even though viruses are very simple, they are still very diverse group
structure can be:
- Naked - non enveloped
- enveloped
- complex capsid
Viral genetic material can be ssDNA/RNA, dsDNA/RNA
- their genes can be wither circular or linear
- Circular dsRNA does not exist
Diversity of viruses
Viruses vary in type of host cell that they can infect
- species specific
- cell/tissue specific
They can infect more than one species/cell type
- just need the right cell receptors on the host
Diversity of viruses: Example
Infects only Humans
- poliovirus
- HIV
- Smallpox
Infects humans and other animals
- Influenza
- Rabies
- Covid
- Ebola
- Measles
Replicating strategies: lytic and lysogenic cycle
- Where genomes are replicated in the infected cell
Replication cycle: lytic, persistent, latent)
one or more rounds of mRNA expression
Virus structure
- virus fall into 2 categories: naked or enveloped
In naked virus, the genome is enclosed by only a capsid-protein shell
The capsid is made of multiple copies of protein subunits called capsomeres
- it could be made from one type of protein or several different proteins
Nucleic capsid - when nucleic acid binds to capsid
A capsomere might bind tightly to a structure on a host or they maybe attachment proteins that protect the outside of the capsid (eg spike proteins)
Enveloped Viruses
have lipid bilayer surrounding their capsid
- lipid bilayer can be derived from the host cell plasma membrane or any other membrane (eg Golgi, ER)
Some enveloped viruses have a matrix later protein just below the enveloped
- eg gp41/120 Hemogluttinate etc
Enveloped glycoproteins are acquired for attachment to host cell
Why do some viruses have envelopes and some don’t
Relates to virus replication cycle
Enveloped: virus buds out through the membrane and acquires envelope without killing the host cell immediately
- Virus replication occurs for long periods of time
- when it leaves the host cell contents are not released into the bloodstream (cuz enveloped)
Naked: cell lyses, all progeny is released at once - cell is dead
- as leave cell, all contents are released to the extracellular environment
Sometimes viruses have complex structure - possess a capsid that is not helical but icosahedral and may have other structures like protein tail or complex outer wall
What is more stable, naked or enveloped
Naked virus is more stable in environment
The envelope may dry out and tear from result of virus structure
- since the attachment protein the virus uses to bind to host cell are in the enveloped - if the envelope is lost, it virus becomes non infectious
cleaning agents like detergent can disrupt envelope - naked viruses are notoriously stable. Poliovirus can persist in chlorinated swimming pool water
Why do we study viruses
They cause disease n humans, wild animals, crops
if understand virus, we can develop a protocol to limit the spread
Enzyme RT and RNases enable pharmaceutical companies to manufacture human products in bacteria or yeast cell
Can also impact society:
- loss of productivity - economics
- allocation of resources - medical facilities, research monies
- closure of public venues, hospitals, schools, airports
- Chaine in social behaviouirs
- Change in policy and education
