Please help with 16-26 16. Protein A and B binds DNA. Which of the following is
ID: 262131 • Letter: P
Question
Please help with 16-26
16. Protein A and B binds DNA. Which of the following is a cooperative DNA binding?
A. If A binds DNA, B binds the same DNA with higher avidity
B. If A binds DNA, B binds a different molecule of DNA with higher avidity
C. The rate of DNA binding by A and B remain the same whether one or the other is bound to DNA
17. Activators may increase the frequency (or rate) of transcription ____________ by ____________
A. initiation/ recruiting RNAP
C. elongation/ allosteric changes of RNAP or elongation factors
B. termination/recruiting rho enzyme to the terminator of the transcript
D. initiation and elongation/ recurring RNAP and allosteric changes of RNAP or elongation factors
E. initiation, elongation and termination/ recruiting appropriate proteins or inducing allosteric changes
18. Inducers are generally _________.
A. proteins
B. nucleic acids
C. small organic molecules
D. any of these organic substances
19. Bacterial activators may bind _________ and repressors may bind________. The best answer will be scored. (UAS- upstream activation sites).
A. UAS/ operator
B. UAS and inducers/ inducers
C. UAS and-or inducers/ operators and-or inducers
D. UAS and-or inducers and-or RNAP/ operators and-or inducers
Regulation by recruitment: example the lac operon
20. Lac operon has three structural genes (Z, Y and A), a promoter, multiple activator binding sites (i.e. UASs) and multiple repressor binding sites (i.e. operators). If you remove (delete) ______ from the gene, there will be minimal or no change in the regulation of the gene.
A. UASs
B. the operators
C. the core promoter
D. the Lac Y or A gene
21. The function of the protein generated from the lacY gene of the lac operon is __________
A. cutting lactose to separate glucose and galactose
B. serving as a membrane transporter
C. detoxification of thiogalactosides
D. converting lactose to allolactose
22. The lac repressor inhibits the transcription of the lac operon mostly by ________.
A. allostery
B. steric hindrance
C. target protein modification
D. cooperative binding of DNA
23. When there is plenty of glucose but no lactose inside the cell, _________.
A. the DNA of the gene will loop and the bound lac repressors will interact with each other
B. the gene will completely shut down and no mRNA will be transcribed from the operon
C. the lac repressor will bind allolactose and two or more of the operators
D. two of these events will take place
E. all of these events will take place
24. Which of the following is the inducer(s) of the lac operon?
A. lactose
B. allolactose
C. cyclic AMP
D. lactose and allolactose
E. allolactose and cAMP
25. When E. coli grows in the presence of both glucose and lactose, all the following will take place except________.
A. the promoter will be de-repressed
B. the operon will be transcribed at the basal level
C. CRP will bind the UAS and activate the operon
D. lac repressor will bind allaolactose and not the operators
E. RNAP-sigma factor will be able to bind the promoter and transcribe the gene
26. Suppose: The number of mRNAs transcribed from the lac operon is (i) 0.01 unit when the operon is repressed, (ii) 2.0 units when the operon is de-repressed (or at the basal level), and (iii) 100 units when the operon is activated by CRP. Which of the following explains 50-fold increase (over the basal level) of transcription by CRP?
A. The CRP-cAMP complex binds the UAS and frequently recruits RNAP/sigma to the promoter
B. The lac promoter is weak thus RNAP/sigma bind the promoter with low affinity
C. CRP-cAMP binds and induces conformational changes in the RNAP/sigma
D. Two of these explain the degree of activation
E. All these explain the degree of activation
Explanation / Answer
16. Option A is correct.
Cooperativity refers to the phenomenon that the binding of one molecule favors the binding of the incoming molecule.
17. Option A is correct.
Activators may increase the frequency (or rate) of transcription initiation by recruiting RNA polymerase.
18. Option C is correct.
Inducers are generally small organic molecules such as Lactose.
19. Option A is correct.
Activators bind to UAS and repressors bind to the operator sequence.
20. Option D is correct.
If we remove a structural gene, it will not affect the regulation of transcription of other structural genes in the operon.
21. Option B is correct.
Lac Z = Beta-galactosidase = required for the hydrolysis of lactose
Lac Y = Permease = required for the transport of lactose
Lac A = Transacetylase
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