FINAL EXAM P2 Flashcards
DNA to DNA
is standard in all cells and is done by DNA polymerase
process is called replication
is done to reproduce the genome
DNA to RNA
is done by RNA polymerase
process is called transcription
is done by every cell on Earth
RNA to RNA
is done by RNA replicase
is only found in viral replication
RNA to DNA
is done by reverse transcriptase
is only found in retroviruses
lytic infection (T4 phage)
in every case where a phage infects a cell, the end result will by lysis and cell death
not all phages kill cells
early middle and late steps must happen in order or reproduction will not be efficient
99.9% of cells choose this pathway
early gene expression
takes over the cellular machinery
middle gene expression
has nucleic acid replication
late gene expression
has capsomers, assembly, packaging, and lysis
takeover
part of lytic cycle
done with the production of nucleases
drives it away from the host to transcribe phage genes. after it makes several copies of its own DNA, late expression begins
nuclease
degrades the host cell genome/DNA
produces its own DNA polymerase
makes its own sigma factor
sigma factor
binds to the host cell RNAP to direct it to a specific set of promoters found on the phage DNA
T4 lysozyme
makes the protein that breaks down PG
can never be lysogenic
lysogenic/temperate phage
aka lambda phage
shuts itself down, turning off its own gene expression so it doesn’t kill the cells. instead, it inserts its genome into the host genome. it stays there silently, not harming the cell; it’s part of the genome
every time the cells replicates its genome, it also replicates the phage genome, passing it on to its progeny
0.1% of cells choose this pathway
prophage
phage is called this when it is inserted into the host cell genome
lysogen
the host strain that carries the prophage
the prophage is in the lysogen
it can be induced, causing the prophage to unsilence itself and start expressing its genes
it will then be excised out of the host DNA and go back into the lytic cycle
induction
caused by DNA damage to the host cell when UV light or chemicals that damage the host DNA
if the cell carrying the prophage is endangered, that cell may die. if it dies, than the phage is dead and will never be able to replicate again. this makes it the right time for the prophage to come out and produce progeny that can hopefully go on and infect other cells
RNA phage (MS2)
an E. coli phage
only has 4 genes. they encode a maturation protein, a coat protein (encodes the capsomer), a lysis protein (eventually lyses the cell), and one for RNA replicase
some of the genes are overlapping into different reading frames. lysis overlaps into the coat and replicase regions. allows for more coding capacity
+RNA in virion
serves as mRNA and as a template for -RNA
key for making the RNA replicase
is packaged into new virus capsids
