viruses prt 2

virus

a nonliving microscopic infectious element that consists of genetic material surrounded by a protein coat and can only replicate inside the cells of a living organism (key features: genetic material, protein coat, replicate inside a cell)

a viruses’ characteristics of living

have genetic code and can reproduce

attachment proteins

attach virus to host cell (found on either capsule or evelope)

protein coat shapes

1. icosahedral

2. filamentous

3. head-tail

icosahedral

shape of a d20 die

filamentous

tubular shape

head-tail

icosahedral on top of a filamentous

virus classification (by genetic material)

dna viruses, rna viruses, retrovirusesd

dna viruses

dna is the genetic code

rna viruses

rna as the genetic code

retroviruses

rna and dna as the genetic code, rna is converted to dna inside the host cell by reverse transcriptase (enzyme that converts rna to dna)

virus life cycle

1. attachment

2. entry

3. replication

4. assembly

5. release

attachment

virus attachment proteins attach to host cell membrane proteins, enveloped viruses have attachment proteins on the envelope, non-enveloped viruses have attachment proteins on the capsule

entry

virus enters the cells — 3 methods of entry

penetration

virus capsule remains outside of the cell and ejects only the genetic material into the cell

fusion

virus envelope fuses with cell membrane, allowing the capsule into the cell

endocytosis

virus “tricks” the cell into pulling inside using endocytosis

replication

the process of copying the virus genetic material and translating virus proteins, dna viruses-replicate in the nucelus, rna viruses- most replicate in the cytoplasm, retroviruses- replicate in the nucleus

assembly

replicated genetic material and proteins are reassembled into new virus particles

release

new viruses are released outside of the cell to go infect a new host cell, 3 methods of release

lysis

cell membrane breaks apart (cell dies)

exocytosis

capsule released via exocytosis

budding

cell membrane becomes viral envelope

lytic cycle (active)

virus dna/rna is not incorporated into host genome, host metabolism is hijacked for virus replication, host eventually dies

lysogenic cycle (dormant)

virus dna is incorporated into host genome, virus remains dormant, host replicates viral dna when it divides, later some trigger may activate the lytic cycle

bacteriophages

“bacteria eater”—only infects bacteria, head-tail protein coat (only bacteriophages have), penetration method of entry

influenza

rna virus, enveloped, infects respiratory epithelial cells, endocytosis method of entry, lytic cycle, replicates in the nucleus

coronavirus

rna virus, enveloped, infects respiratory epithelial cells, endocytosis method of entry, lytic cycle, replicates in the cytoplasm

hiv—human immunodeficiency virus

retrovirus, enveloped, infects helper t cells (white blood cell), fusion method of entry, lysogenic cycle (switching to lytic cycle causes aids), replicates in the nucleus

why is hiv so hard to fight off

lysogenic infection of immune cells makes this virus nearly impossible to fight off

rabies

rna virus, enveloped, filamentous capsule, infects central nervous system, lytic cycle, fusion method of entry, replicates in the cytoplasm, can pass blood-brain barrier

viroid

infectious rna, no protein coat (capsule), rna will self replicate in host using host’s proteins, infect angiosperms only

prion

infectious protein, no genetic material, misfolded protein that causes others proteins of the same type of misfold, common in animals—often the result of cannibalism