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Exam 12: Control of Gene Expression

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Question 41

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What would happen to the lac operon in the absence of allolactose?

A) The structural genes within the lac operon will be constitutively transcribed.
B) The activator protein will be bound to the operator, which will turn on the structural gene behind it.
C) The repressor regulator protein binds to the operator and prevents the transcription of the structural gene.
D) The catabolite activator protein becomes inactivated and no transcription occurs.
E) The cAMP level rises in the absence of allolactose, which in turn inactivates the transcription.

F) A) and D)
G) C) and E)

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Question 42

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An E.coli strain of chromosomal genotype lacI^- lacP⁺ lacO⁺ lacZ⁺ lacY⁺ constitutively expresses the genes of the lac operon.The strain is converted to wild-type lac operon regulation by the addition of an extra piece of DNA.What gene or genes are contained on this extra DNA that explain this conversion to wild type? Include an explanation of cis- or trans-acting factors and how they work.

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The extra piece of DNA contain...

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Question 43

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In corn, red kernels (PP)are typically dominant to white kernels (pp).A red plant was crossed to a white plant to produce a Pp heterozygote with red kernels.However, a partially white kernel appeared unexpectedly.This kernel was grown into an adult plant, and for several generations of crosses, all the offspring of this original kernel had a mix of partially red and partially white kernels.However, when the seeds were grown in the presence of a demethylating drug, all of the resulting plants had red kernels.Explain why the mixed color kernel appeared, why the offspring of this kernel also had the mixed color phenotype, and why the demethylating drug had its effect.

How is the epigenetic trait induced by vinclozolin transmitted to offspring?

In the nematode roundworm, Caenorhabditis elegans, the LIN-14 protein controls the timing of certain cell divisions during development.LIN-14 protein levels are normally high in early development but decrease in the later stages.In a lin-4 mutant, the level of LIN-14 protein stays high throughout development, changing the pattern of cell divisions in the animal and producing defects in the shape of the animal.The lin-4 gene encodes a microRNA that binds to a sequence in the 3'UTR of the lin-14 mRNA. a.How does the lin-4 microRNA likely regulate LIN-14 protein levels? Explain why the lin-4 mutant has high levels of LIN-14 throughout development. b.Mutations in the 3' UTR of lin-14 have been identified that alter the sequence to which lin-4 normally binds.What effect would these mutations be expected to have on the expression of LIN-14 protein in the animal?

What is the consequence of methylation of DNA sequence called CpG islands?

Which gene control mechanisms from the previous question are NOT used in prokaryotes, and why?

If there are mutations that inactivate lacP and lacI, which of the following is true? (I = lac repressor gene; Z, Y, A = lac operon structural genes; P = lac promoter; O = lac operator)

Where would the lac repressor be bound in a (nonmutant) E.coli cell that is growing in low glucose and high lactose? (I = lac repressor gene; Z, Y, A = lac operon structural genes; P = lac promoter; O = lac operator)

When siRNAs are present, the rate of mRNA degradation _____ and the rate of protein production _____.

Explain why glucose-dependent catabolite repression in E.coli is important and how it is possible to achieve this repression without influencing glucose metabolism.

How would you expect DNA methylation to alter gene expression?

Which of the following is NOT an example of epigenetics?

If the lacY gene is turned off when lactose is absent, how do the first molecules of lactose enter the cell to induce transcription of the all three lac operon genes?

Over the past decade, a significant finding in biology has been the identification of miRNAs and siRNAs and their role in regulating the development of many multicellular organisms.Briefly describe the four different ways these small RNAs influence gene expression.

Which of the following statements about response elements is INCORRECT?

Aside from the case of lacO^c, where the operator is unable to bind to the repressor protein, briefly describe another mutant that could have caused constitutive expression of lac operon.

Which one of these is NOT an advantage of using Arabidopsis thaliana as a model organism?

How is foreign DNA transferred into Arabidopsis?

Insulators can block the effects of enhancers only when they lie: