A Genetic Switch
Card Set Information
A Genetic Switch
How many base pairs in 1 turn of the helix?
10 base pairs
mRNA is read at what end?
begins reading at the 5' end
Binding of a protein to the operator is dependant on these two factors
what triggers a lambda virus to enter to lytic cycle?
cI gene encodes for?
which is stronger: the ionic bond or the hydrogen bond?
Ionic bond is stronger
The lambda repressor is what type of regulator?
both negative and positive. It turns off all genes but turns on its own gene.
Cro protein is responsible for?
promotes and is required for lytic growth
Which gene (cI or cro) can be transcribed without a regulatory protein?
promoter (cI gene)
about ____ of the repressor proteins are found as dimers
dimerization of the repressor protein can be increase by:
Repressor dimers use which end to bind to the DNA major groove?
cro exists as a _____ in the cell
dimer (nearly 100% of the time due to high affinity to form a dimer)
How does the principle of exclusion apply to lambda phage?
Repressor at O
2 turns off cro gene by preventing of RNA polymerase to P
How does repressor act as a positive control?
Repressor at O
2 helps RNA polymerase bind and begin transcription at P
to transcribe cl (increase in roughly ten-fold)
What would happen if the Gln-Ser sequence in helix 3 of the
was altered? What if the same sequence was altered in
both of these signals are responsible for the recognition of the promoter.
Gln recognizes A
Ser recognizes G
How does repressor/Cro protein distunguish between operator sites?
amino acids other than Gln-Ser
Which characteristics can contribute to the affinity to either Cro or repressor; allow it to distinguish operators?
the tightness of binding
interactions between other parts of the protein and DNA
in lamda represson, the end of it's flexible arm
A characteristic which differs P
has a much better match at -35 and -10 region then P
, thus it transcribes freely
needs lambda repressor at O
What is the effect of binding at O
1 with either Cro or repressor?
RNA polymerase is excluded from P
because bound protein covers part of the surface of DNA helix that must be copied.
What is the effect when either Cro or repressor binds to O
the protein would block RNA polymerase from transcribing P
What is the effect of repressor bound at O
turns OFF P
overlapping the DNA surface
Name the effect if Cro is bound at O
fails to stimulate P
it also lacks the specific amino acids along the contacting surface that would favorably interact with RNA polymerase
What characteristic is paramount to the function of the Lamda switch?
the overlapping regions of the promoters and the operators
additionally, the regulation by the proteins
The TATAA box of the promoter is found in what region?
Cro at O
2 blocks polymerase from binding to P
Which gene does the repressor turn on?
it's own gene
of the viral circular DNA refers to?
the attachment site
When phage DNA is injected into the bacteria, it is linear. Next it becomes circular. Describe the process of how it becomes circular.
The DNA has an overhang (lots of C's and G's) that automaically anneal and are joined by a bacterial enzyme
known as the
site (cohesive ends)
if the phage enters a lysogenic cycle, only these 2 genes are expressed.
the N protein is a _____ regulator?
The N protein turns on 9 genes. What genes does it not turn on?
N protein only interacts with 1 promoter which turns ON
cIII , xis,
While N protein does interact with P
to turn on those genes, it can also interact in the opposite direction with P
What is the importance of the Q protein?
Q protein is an anti-terminator which allows transcription to proceed right and transcribe genes for lysis such as:
N protein, like Q protein, is also an anti-terminator
True (pg 53)
How does repressor synthesis begin in the absence of repressor?
can be transcribed from 2 promoters, one is activated by the repressor, but the other one is activated by CII protein