Chapter 16: Control of Gene Expression in Prokaryotes Flashcards
Structural Genes
encoding proteins that “make or break”
Regulatory Genes
encoding products that interact with other sequences and affect the transcription and translation of these sequences
Regulatory Elements
DNA sequences that are not transcribed but play a role in regulating other nucleotide sequences
What makes expression constituitive?
if a gene is continuously expressed under normal cellular conditions
If a cell is undergoing catabolite repression, what kind of control is it undergoing?
Positive
What type of positive control uses CAP, cAMP, and glucose to repress the metabolism of other sugars?
Catabolite repression
Where do CAP and cAMP bind?
slightly upstream of the lac gene promoter
What is inversely proportional to the level of available glucose?
cAMP
What is positive control?
-stimulate gene expression by using a regulatory protein is an activator
-has to be turned on
How does catabolite repression function when glucose is low?
-levels of cAMP are high and it readily binds to CAP. ONce binded to the DNA, DNA polymerase increases binding efficiency
-RESULTS: high rates of transcription and translation of structural genes AND the production of glucose from lactose
How does catabolite repression function when glucose is high?
levels of cAMP are low and less likely to bind to CAP. RNA polymerase cannot bind as efficiently so transcription is low
What is negative gene expression?
-needs to be turned off
-inhibit gene expression; regulatory protein is a repressor
What stage are most proteins regulated in?
transcription
What are the different shapes within a protein?
domains
What is significant about the domains of a protein?
~60-90 amino acids that are responsible for binding to DNA and forms hydrogen bonds
What is the specific shape that is found within a domain?
motif
What is significant about motifs?
a simple structure that fits into the major groove of the DNA
What is a helix-turn-helix motif?
-regulatory in prokaryotes
-contains a DNA-binding helix, turn, then a dimer binding helix
What is the signifigance of a zinc finger motif?
eukaryotic regulation
What is the signifigance of a leucine zipper motif?
eukaryotic regulation
What is an operon?
group of genes sharing a common promoter and are transcribed as a unit
What is a promoter+ additional sequences that control transcription (operator)+ structural genes?
operon
Are operons more common in prokaryotes or eukaryotes?
typical in prokaryotes but not in eukaryotes
How were operons discovered?
found by investigating decision of E.coli to eat glucose or lactose
What is a regulator gene?
DNA sequence that encodes products that affect the operon function, but are not part of the operon
How can regulator genes regulate transcription of mRNA?
regulator genes must have their own promoter that encodes for a regulatory protein. It must then bind to the operator site
What type of operon has transcription off and needs to have it turned on?
inducible operons
What type of operon has transcription turned on and needs it be turned off?
repressible operon
What is the function of the lac operon?
it is a negative, inducible operon that functions in lactose metabolism
What is the inducer in the lac operon?
allolactose
lacI
repressor encoding gene
lacP
operon promoter
What is contained in the lacP?
-35 and -10 consensus sequences
lacO
operon operator
lacZ
encoding B-galactosidase
lacY
encoding permease
What is the function of permease?
actively transprots lactose into the cell where B-galactosidase breaks it into galactose and glucose
What is the function of B-galactosidase?
-breaks lactose into glactose and glucose and the related compound of allolactose (to then be converted to galactose and glucose)
lacA
encoding transacetylase
Does the repression of the lac operon completely shut down transcription?
no
How does the regulatory protein function in the absence of lactose?
the repressor binds to the operator and inhibits transcription
What does it mean that the lacI+ gene is transdominant?
the repressor produced can bind to both operartors and repress transcription in the anbsence of lactose
How does the regulator protein function in the prescence of lactose?
some of the lactose is converted to allolactose. This binds to the regulator protein making it inactive
What happens to the structrual genes of of the lac operon in the prescence of lactose?
they are transcribed and translated since the regulator cannot bind to the operator
When is functional B-galactosidase produced from the lacZ+ gene?
when lactose is present and it has inactivated the repressor
What does the lacI gene produce in the prescence of lactose?
a super repressor that does not bind lactose and is transdominant
What is a partial diploid?
full bacterial chromosome+ an extra piece of DNA on F plasmid
How does the partial diploid function in the absence of lactose?
active represssor binds to the operator which creates B-galatosidase
How does the partial diploid function in the prescence of lactose?
lactose binds to the repressor, which inactivates it and produces nonfunctional B-galactosidase
What affects the structure of the enzymes but not the regualtion of their synthesis?
structural gene mutations
Where do structural gene mutations occur and affect?
only affect lacZ or lacY and only occur on lacZ/lacY
What affects the transcription of trans structrual genes?
regulator gene mutations
What gene leads to constitutive transcription of three structural genes?
lacI-
What is dominant over lacI- and is trans acting?
lacI+ is dominant and a single copy brings about normal regulation of lac operon
What do operator mutations affect?
affect transcription of structural genes; cis
Is an operator mutation dominant or recessive?
dominant over lacO+
What do promoter mutations affect?
transcription of structural genes
What is the trp operon?
a negative repressible operon that is composed of 5 structural genes
What works together to convert chorismate to trytophan?
-the 5 structural genes
-trpE, trpD, trpC, trpB, and trpA
How does the trp operon function when trp is low?
the trp repressor is noramlly inactive and cannot bind to the operator so transcription occurs
How does the trp operon function when trp is high?
trp binds to the repressor and activates it. The repressor then binds to the operator and shuts transcription off
What affects the continuation of transcription, not its initiation?
attenuation
What action terminates transcription before it reaches the structural genes?
attenuation
How does attenuation work in the trp operon when trp is high?
region 1 binds to region 2, which causes the binding of region 3 and 4
-premature transcription termination
How does attenuation work in the trp operon when trp is low?
region 2 pairs with region 3 and termination does not occur in transcription
Antisense RNA
complementary to targeted partial sequence of mRNA; they function by going to influence translation somewhere else
Riboswitches
molecules influence the fomration of secondary structures in mRNA; RNA that has to bind to an RNA molecule to allow it to be linear and disrupt base pairing to prevent translation
Ribozymes
mRNA molecules with catalytic activity
