chapter 19: viruses

capsid

protein enclosing viral genome

viral envelope

membrane surrounding the viral capsid, made from host membrane and viral parts

bacteriophage

virus that infects bacteria

lytic cycle

reproductive cycle of viruses which results in host cells being destroyed and releasing progeny viruses

lysogenic cycle

reproductive cycle resulting in viral genome being engrained into host cell, letting the host cell continue living and viral genome being passed onto daughter cells. creates prophages

virulent phage

virus that only uses lytic cyclet

temperate phage

virus that can use lytic and lysogenic cycle

prophage

result of lysogenic cycle

provirus

viral DNA in host DNA as a permanent part of it

is a virus living or nonliving

a nonliving because it requires other cells for duplication

virus componente

• elongated capsid head that contains genome

• protein tail piece used to inject genetic info into host

factors controlling phage entering lytic vs. lysogenic cycle

environmental conditions control this. if the environment is stressful (starvation or toxic chemicals) will cause virus to use lytic cycle

advantage of lysogenic cycle

allows for host cell to live

basis of animal virus classification

• DNA or RNA

• single or double stranded

reproductive cycle of retroviruses (HIV)

virus will use reverse transcriptase to incorporate viral RNA in host DNA

function of reverse transcriptase

used by retroviruses to put viral genome in host DNA

emerging virus and how its caused

• a new virus

• from mutations, dissemination from isolated human pop., or transferred from different species

viroid

circular RNA molecule that infects plant cells and affects growth

prion

slow-acting, virtually indestructible infectious protein. propagates by turning normal proteins in prions

2 characteristic of prions that make it hard to control

• hard to detect

• brain disease

• don’t know you have until too late