Viruses Flashcards
shared features of viruses
- non-cellular (no cytoplasm, metabolism, enzymes)
- obligate intracellular parasites
- multiple origins (no shared ancestor)
- small, fixed size (smaller than the host cell, lack structural features, do not grow)
- nucleic acid as genetic material (same as host cell - where their proteins are synthesized, same genetic code)
- capsid made of protein subunits
which enzymes do viruses have
- replication of genetic material
- infecting host cells
- lysis (bursting hist cells)
what kind of genetic material can viruses have
- double/single-stranded RNA which can be circular/linear
- double/single-stranded DNA which can be positive/negative sense
positive vs negative sense
positive sense - can be used immediately as mRNA - negative has to be transcribed before translation
diversity of viruses
- genetic diversity - no genes occur in all viruses
- structural diversity (can be enveloped or non-enveloped)
virus membrane is made out of
phospholipids (from the hosts’ plasma membrane (lysis))
glycoproteins (from the virus)
virus membrane function and which viruses have it
helps the virus to make contact and infect the host cell
animal viruses are enveloped
(plant and bacteriophages are mostly non-enveloped)
Influenza virus
- infects epithelial cells of respiratory system
- eight single-stranded negative-sense RNA
- enveloped
- RNA-replicase enyzme
TMV (Tobacco Mosaic Virus)
- infects plant cells
- one single-stranded positive-sense RNA
- non-enveloped
- 1st discovered virus
Bacteriophage
- infects bacteria
- one double-stranded DNA
- non-enveloped
COVID-19
- infects epithelial cells of human respiratory system
- single-stranded positive-sense RNA
- enveloped (have spike proteins on the capsid - receptors, initiate fusion of the virus with the host cell)
HIV
- infects human T-lymphocyte cells (a type of white blood cell that is a part of the immune system - develop in bone marrow)
- two single-stranded positive-sense RNA
- enveloped
- retrovirus - converts RNA to DNA - reverse transcriptase (has the highest mutation rate)
lytic cycle
virus attaches and injects its genetic material which produces viruses inside of the host cell and then bursts it
steps of lytic cycle
1|attachment (to a host cell using tail fibers)
2|penetration - genetic material entered via tail and pores in the membrane
3|DNA replication (100 copies)
4|sythesis of viral proteins - using mRNA transcribed from viral genetic material
5|assembly (of new viruses)
6|lysis (host bursting)
lysogenic cycle
viral genetic material becomes integrated into the host cell’s genetic material - virus is temperate in this state because it does not kill its host (causes minimal harm) - daughter cells of the host inherit the undetected and inactive viral genes - stimulus for lysis can come from inside or outside of the host
- steps the same as in lytic but with integration
