Genetics Exam 3 Chapter 16
Ribozymes
mRNA molecules with catalytic activity
A key factor controlling attenuation in the trp operon is the number of tRNA molecules charged with ___
tryptophan
Partial diploid
Bacterial cell that possesses two copies of genes, including one copy on the bacterial chromosome and the other on an extra piece of DNA (usually a plasmid)
B-galactosidase
breaks down lactose into glucose and galactose, or allolactose
How many promoters are typically found in a four-gene operon?
1
attenuator
1+2 and 3+4 combine when trp levels are high
antiterimator
2+3 when trp levels are low
helix-turn-helix
A protein domain composed of two α helices joined by a short strand of amino acids and is found in many DNA binding proteins. (major groove)
Inducer
A specific small molecule that binds to a bacterial repressor protein and changes the repressor's shape so that it cannot bind to an operator, thus switching an operon on.
Operon
A unit of genetic function common in bacteria and phages, consisting of coordinately regulated clusters of genes with related functions.
positive repressible operon
Active activator, transcription is on and needs to be turned off. Inducer binds to activator making it inactive, transcription is turned off.
negative inducible operon
Active repressor, transcription is off and needs to be turned on. Substrate makes repressor inactive and transcription is turned on. ex: lac operon
Motif
Actual part of the protein that fits into the major groove, different proteins will stick to different parts of the groove
Attenuation occurs when during the process of transcription?
After transcription begins
Trp operon
An example of a repressible operon
repressible operon
An operon under negative control. It is always turned on unless triggered to turn off.
Inducible operon
An operon under positive control. It is usually "off" but can be turned "on".
inducible operon
An operon under positive control. It is usually "off" but can be turned "on".
When glucose is low...
CAMP is high, bind to CAP; Transcription is on
When glucose is high...
CAMP is low, cannot bind to CAP; Transcription is off
Regulator gene
DNA sequence encoding products that affect the operon function, but are not part of the operon- on different part of the gene
Riboswitches
Folded RNAs that act as switches regulating protein synthesis in response to environmental conditions
Assume that a deletion mutation occurs within the trp operon so that the DNA corresponding to the last (distal) part of region 1 and the first (proximal) part of region 2 of the mRNA 5′ UTR is removed. What will be the effect of this deletion on the expression of the trp structural genes?
In the absence of tryptophan, transcription of the structural genes will be reduced compared to a wild-type operon.
positive inducible operon
Inactive activator, transcription is off and needs to be turned on. Substrate binds and makes the activator active, transcription is turned on.
negative repressible operon
Inactive repressor, transcription is on but needs to be turned off. Corepressor binds to repressor making it active and transcription is turned off. ex: trp operon
Which of the following is the most accurate description of gene expression regulation by riboswitches?
It involves a regulatory sequence within a mRNA that binds to some small molecule and alters mRNA secondary structure.
Genes that encode proteins which are used in metabolism or biosynthesis are called _____ genes.
Structural
catabolite repression
System of gene control in some bacterial operons in which glucose is used preferentially and the metabolism of other sugars is repressed in the presence of glucose.
In the absence of tryptophan, what happens in the trp operon when the ribosome stalls at the tryptophan codons?
The attenuator forms and transcription terminates.
A mutation in the 5ʹ UTR of the trp operon reduces the ability for region 2 to pair with region 3. What would be the effect of this mutation on the trp operon when tryptophan levels are high?
The mutation would have no effect on the trp operon.
When a structural gene is under negative inducible control, what would be the result of a mutation that eliminates the regulatory protein?
The structural gene will be constitutively expressed due to the lack of an active repressor.
What happens when 2 and 3 region come together?
Transcription continues
corepressor of trp operon
Tryptophan
A mutation occurs that causes the lac operon to be unable to be induced in the presence of lactose and absence of glucose. This same mutation also causes other sugar operons such as ara, mal and gal to also become uninducible. What mutation would most likely cause this phenotype?
a mutation in the structural gene for CAP
Antisense RNA
a single-stranded RNA molecule complementary to, and thus targeted against, an mRNA of interest to block its translation
Corepressor
a small molecule that binds to a bacterial repressor protein and changes the protein's shape, allowing it to bind to the operator and switch an operon off
zinc finger
a small protein structural motif that is characterized by the coordination of one or more zinc ions in order to stabilize the fold (major groove)
structural gene mutation
affect the structure of the enzymes, but not the regulations of their synthesis
cAMP
cyclic adenosine monophosphate- the concentration is inversely proportional to the level of available glucose
Gene regulation in bacteria cells _____
allows the bacteria to respond to environmental changes
When cellular tryptophan levels are low, regions 2 and 3 of the 5ʹ UTR pair and form the 2+3 structure called _____.
anti-terminator
An additional level of operon control that results in premature termination of transcription is called _____.
attenuation.
Enhancers are typically found _____ the gene they affect
away from
In the presence of allolactose, the lac repressor _____
cannot bind to the operator.
Many genes in various types of cancer cells are expressed inappropriately, causing the cancer cells to grow unchecked and mutate without repair. Which type of gene is NOT likely to be inappropriately expressed in these cells?
constitutive
A point mutation in region 1 of the 5ʹ UTR converts UGG to UGU. In the absence of cysteine, this mutation would most likely result in _____.
continued transcription of the trp operon in both the absence and presence of tryptophan.
constitutive expression
continuously expressed under normal cellular conditions
A _____ binds to the repressor and makes it capable of binding to the promoter.
corepressor
lacZ
encodes B-galactosidase
lacY
encodes lactose permease
lacA
encodes transacetylase
Negative operon control
has a repressor regulator protein
Positive Operon control
has an active regulator protein
Where is a repressor encoded?
in the regulatory genes
A mutation at the operator site prevents the regulator protein, which acts as a repressor, from binding. Constitutive expression results from the operon. This is an example of a(n) _____ operon.
inducible
Antisense RNA molecules typically _____.
inhibit translation
Which of the following genotypes will result in a lac operon that produces β-galactosidase, both when lactose is present and when it is absent?
lacIs lacP+ lacOc lacZ+ lacY-
operator mutations
lacOc, lacOc is dominant over lacO+, which is cis acting. C=constitutive
Promoter mutations
lacP-, cis acting
lac operon structural genes
lacZ, lacY, lacA
regulator gene mutations
lacl- leads to constitutive transcription of three structure genes. lacl+ is dominant over lacl- and is trans acting. A single copy of lacl+ brings about normal regulation of lac operon.
The lac operon would produce the greatest amount of β-galactosidase when _____.
lactose is present but glucose is absent.
Domain binding proteins
large region that sticks to DNA by forming hydrogen bonds
trp operon
negative repressible operon; when trp is low, regulator stays inactive and transcription is on. when trp is high, tryptophan binds to the regulator protein to make it active and stops transcription.
The trp operon is an example of a _____ and _____ operon.
negative; repressible
Can cAMP mutate?
no
lacZ+lacY-/lacZ-lacY+
normal phenotype
The regulator protein binds the _____ of the operon.
operator
Where do repressors bind?
operator
Where does the repressor protein bind?
operator
lacO
operator
Operator in lac operon
overlaps the promotor and the first structural gene
Which level of gene control is matched appropriately to a regulatory mechanism?
post-translation modification - activation of a protein by cleaving it
Attenuation
premature termination of transcription when 3 and 4 region of 5'UTR trp operon come together
A mutation in the 5ʹ UTR of the trp operon results in region 2 always pairing with region 3. The effect of this mutation on the trp operon when tryptophan levels are high would be that the mutation would _____.
prevent attenuation from occurring- Attenuation results in premature transcription termination. The pairing of 2 and 3 results in antitermination, and transcription will occur in this mutant.
Where does RNA polymerase bind?
promoter
lacP
promoter
Where do activators bind?
promotor
operon
promotor + additional sequences that control transcription (operator) + structural genes
regulatory proteins
proteins involved in the expression of control genes- controls of operon is on or off
If you wanted to increase the level of transcription of the trp operon, which type of control, when mutated and rendered ineffective, would give you a larger effect?
repression
lacl
repressor encoding gene
Some mRNA molecules contain regulatory sequences called _____, where molecules can bind and affect gene expression by influencing the formation of secondary structures in the mRNA.
riboswitches
Attenuation of the trp operon involves _____.
secondary structure formation in RNA molecules, untranslated regions of RNA, high tryptophan levels, and 5' UTR
Antisense RNA molecules are _____.
small RNA molecules that are complementary to DNA sequences
leucine zipper motif
structural motif in many DNA binding proteins in which two alpha helices from separate proteins are joined together in a coiled coil. leucines interact with one another and form zipper shape
Trans acting genes can control expression of genes on _____ DNA molecules, while cis acting genes can control expression of genes on _____ DNA molecules.
the other; the same
Repressible operon
transcription is usually on, but can be turned off
Permease
transports lactose into the cell
The attenuator structure of a hairpin followed by a string of uracil nucleotides is similar to the structure of a bacterial intrinsic terminator.
true
When tryptophan levels are high, regions 3 and 4 of the 5ʹ UTR pair, followed by a string of _____ nucleotides.
uracil
In the trp operon, when does translation keep up with transcription?
when tryptophan levels are low and regions 2 and 3 form a hairpin
Promoter
where RNA polymerase binds and starts transcribing