Exam #4 (CH 14)
What two ways do inducers cause transcription to increase?
1. binds to repressor proteins to prevent its binding to DNA 2. Bind to activator protein to cause it to bind with DNA
What three things can occur in the regulation of gene expression which prevent TRANSLATION from starting?
1. translational repressor proteins bind to mRNA 2. riboswitches produce mRNA conformation 3. Antisense RNA bind to mRNA
Consider the data presented on pg 353 from the Jacob and Monod experiments with partial diploids. In the two mutant strains, what was the percentage of beta-galactosidase when lactose was added or not added? Just put the number and don't include the % sign.
100
Regulatory proteins that respond to small effector molecules typically have _____ (number) binding sites. What are these binding sites for?
2. One for DNA the other for the effector molecule
Which of the following encodes a trans-acting factor? A. lacP B. lacO C. lacI (i) D. CAP site
C
a repressor is a _____ that ______ transcription. a. small effector molecule, inhibits b. small effector molecule, enhances c. regulatory protein, inhibits d. regulatory protein, enhances
C
Assume a test was conducted with two mutants (lacI- and lacO-) with no F' factor present. What would be true of expression of the lac operon between these two mutants with and without lactose? A. The lacI- mutant would have higher expression than the lacO- mutant under both conditions. B. The lacI- mutant would have lower expression than the lacO- mutant under conditions with lactose. C. The lacI- mutant would have lower expression than the lacO- mutant under conditions with no lactose D. Both mutants would have similar expression under both conditions.
D
What is associated with allosteric regulation? a. allolactose b. allolactose and glucose c. allolactose and cAMP d. allolactose, cAMP and glucose
D
What would expression of beta-galactosidase and permease be in a high glucose, high lactose environment be compared to an environment with no glucose and high lactose? In other words, you are describing expression how expression would differ in high glucose and high lactose conditions. Assume there are no mutations to genes associated with the lac operon. A. Expression of both beta-galactosidase and permease will be greater. B. Expression of beta-galactosidase will be greater but expression of permease will be less. C. Expression of permease will be greater but expression of beta-galactosidase will be less. D. Expression of both beta-galactosidase and permease will be less. E. It isn't possible to determine based on the provided information.
D
What is the CAP site?
DNA sequence recognized by an activator protein called the catabolite activator protein (CAP)
what are F' factors?
F factors that also have genes from the bacterial chromosome
A lac operon has a mutation in the lac I gene that results in the production of a nonfunctional protein. Under conditions of no lactose, what would you predict to be true about the relative expression of beta-galactosidase and permease in this situation? A. Expression of both beta-galactosidase and permease will be greater. B. Expression of beta-galactosidase will be greater but expression of permease will be less. C. Expression of permease will be greater but expression of beta-galactosidase will be less. D. Expression of both beta-galactosidase and permease will be less. E. It isn't possible to determine based on the provided information.
a
Which of the following conditions would cause transcription to be activated within the lac operon? a. repressor and inducer b. repressor and corepressor c. activator and inhibitor d. none of the above
a
What is a merozygote?
a bacteria containing F' factors, a partial diploid
What does the term "induced" mean in regulation?
a gene that has been transcriptionally activated by an inducer
What are cis-acting factors?
a regulatory protein that binds to a regulatory element in DNA that has a cis effect
What are trans-active factors?
a regulatory protein that binds to a regulatory element in the DNA and has a trans effect
What is allosteric regulation?
action of a small effector molecule
What is the role of allolactose in regulation?
acts as small effector molecule for lac operon
What is polycistronic mRNA?
an RNA that contains the sequences of two or more genes. (encoded by operon0
If a gene is repressible and under positive control, describe what effector molecule and regulatory protein it has.
an inhibitor molecule and an activator protein.
How does an effector molecule play a role in transcriptional regulation?
binds to a repressor or activator, causing conformational change in the regulatory protein which influences whether the protein can bind or not to DNA.
Consider the following bacterial strain, in the absence of lactose, is beta-galactosidase and/or permease made? F'/I-P+C-Z+Y+/I+P+O-Z-Y- If the normal produces 100% beta-galactosidase....what would this partial diploid make?
both beta-galactosidase and permease It would make 50% because the second chromosome section doesn't make beta-galactosidase
How does exposing an E. coli cell to glucose affect the regulation of the lac operon via CAP?
cAMP doesn't bind to CAP and stranscription DECREASES
The lac operator site is is an example of a ____-acting element (cis/trans)
cis. because it doesn't defuse, it helps the genes next to it
Unregulated genes are also called ____________ genes (one word)
constitutive genes
___________ genes (one word) encode proteins needed for survival. In contrast, the majority of genes are _______ so that the proteins they encode can be produced at the proper times and in proper amounts (one word)
constitutive, regulated
What is cAMP?
cyclic AMP. small effector molecule produced from ATP via an enzyme known as adenylyl cyclase
What did the analysis of mutations in the lac operon reveal?
each protein involved with lactose utilization is encoded by a separate gene
In conjunction with regulatory proteins, small __________ (one word) molecules play a critical role in transcriptional regulation.
effector
What binds to allosteric sites?
effector molecules
What is the role of the lacZ gene?
encodes enzyme B-GALACTOSIDASE that cleaves lactose into galactose, allolactose and glucose.
what is the role of the lacY gene?
encodes lactose PERMASE, required for transport of lactose into the cytoplasm of the bacterium
What is the role of the lacI gene?
encodes the lac repressor, a protein that regulates the lac operon by binding to the operator site and repressing transcription
What are repressible genes?
genes that are regulated by repressors and inhibitors
What are inducible genes?
genes which are regulated by a small effector molecule that increases transcription, an inducer.
What is a trans-effect?
genetic regulation that can occur even though two DNA segments are not physically adjacent.
What substance directly acts to decrease the concentration of active CAP protein? One word.
glucose
What is an operon?
group of two or more genes under the transcriptional control of a single promoter
what is the most common way to regulate gene expression in bacteria?
influencing the rate at which transcription is initiated. The rate of RNA synthesis can be increased or decreased
What lac gene is NOT in the operon?
lacI
What genes are under the control of the lac promoter?
lacZ, lacY, and lacA
What is lactose made of?
made of glactose and glucose
On its chromosome an E. coli cell as lacI-, lacZ+, lacY+, lacA+. It has an F' factor that is lacI+, lacZ+, lacY+, and lacA+. What is the expected level of expression of the lac operon genes in the absence of lactose?
neither lac operon whould be expressed
Is the lacI gene part of the lac operon?
no, its its own second transcriptional unit
For transcription to take place, an operon is flanked by a _______ that signals the beginning of transcription and a _______ that specifies the end of transcription
promoter, terminator
Enzyme adaptation is due to the transcriptional __________ of genes (one word)
regulation
What is negative control vs. positive control?
regulation by a repressor protein is negative control, regulation by an activator protein is positive control
What is a repressor?
regulatory protein that binds to the DNA and inhibits transcription
What is an activator?
regulatory protein that increases the rate of transcription.
In most cases, transcriptional regulation involves ___________ (two words) that bind to the DNA and affect the rate of transcription of one or more nearby genes
regulatory proteins
What are the two types of regulatory proteins?
repressors and activators
What is the operator site?
sequence of bases that are the binding site for the lac repressor
What is an inducer?
small effector molecule that causes transcription to increase
What is lactose?
sugar found in milk
What is the key benefit of gene regulation?
the encoded proteins are produced only when they are required, this doesn't waste energy
What happened when jacob and Monod exposed bacterial cells to lactose?
the levels of lactose-utilizing enzymes increased by 1000-10,000 times
What is diauxic growth?
the sequenctial use of two sugars y a bacterium
Is the action of the lac repressor on the lac operon a _______ effect (cis/trans)
trans
What is the difference in mediation between trans-effect and cis effect?
trans-effect is mediated by genes that encode regulatory proteins, whereas a cis-effect is mediated by DNA sequences that are binding sites for regulatoy proteins
What is catabolite repression?
transcriptional regulation that is influences by the presence of glucose (which is a catabolite, broken down inside the cell)
what is enzyme adaptation?
when an enzyme only appears within a living cell after the cell has been exposed to the substrate for that enzyme
Under what condition is the lac repressor bound to the lac operon?
when it is not exposed to lactose—when allolactose is not bound to the repressor.
What is gene regulation?
when the level of gene expression can vary under different conditions (compared to unregulated genes which have constant levels of expression in all conditions over time)
