Genetics Chapter 16 – Flashcards
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Genetic regulation in eukaryotes can take place at a variety of levels from transcriptional to post-translational. At what level is genetic regulation considered most likely in prokaryotes?
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transcriptional
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This question relates to the regulation of enzymes involved in the synthesis of tryptophan in E. coli. If tryptophan is present in the medium and available to the bacterium,
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the repressor is bound to the operator, thus blocking transcription.
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Under the system of genetic control of the tryptophan operon,
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when there is no tryptophan in the medium, transcription of the trp operon occurs at high levels.
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What term refers to a contiguous genetic complex that is under coordinate control?
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operon
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What term would be applied to a regulatory condition that occurs when protein greatly reduces transcription when associated with a particular section of DNA?
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Negative control
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When referring to attenuation in regulation of the tryptophan operon, it would be safe to say that when there are high levels of tryptophan available to the organism,
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transcriptional termination is likely.
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Which of the following terms best characterizes catabolite repression associated with the lactose operon in E. coli?
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Positive control
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Which term most appropriately refers to a regulatory protein in prokaryotes?
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DNA binding protein
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What is meant by polycistronic mRNA? Give an example.
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Polycistronic mRNA can be translated in to more than one protein. The tryp operon is an example. The one mRNA can be translated into 5 different proteins.
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Present a detailed description of the actions of the regulatory proteins in inducible and repressible enzyme systems.
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In inducible enzyme systems, a repressor protein is bound to the operator at all times. When a certain molecule is present and binds to the repressor protein, it changes its conformation so that it can no longer bind to the operator. This allows the polymerase to bind and transcription occurs.
In repressible enzyme systems, a repressor protein is present in the environment, but in the wrong conformation. When a certain molecule is present and binds to the repressor protein, it changes its conformation so that it can bind to the operator. This prevents polymerase from binding and transcription stops.
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Certain mutations in the regulator gene of the lac system in E coli result in maximal synthesis of the lac proteins (β-galactosidase, etc.) even in the absence of the inducer (lactose). Provide an explanation for this observation.
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If there is a mutation in either the repressor gene or the operator binding site, translation will continue. A mutation in the repressor gene will either make a non-functional repressor protein or not make one at all. A mutation in the operator binding site will not allow the repressor protein to bind. Both of these situations mean the polymerase can bind even in the absence of lactose.
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The following table lists several genotypes associated with the lac operon in E. coli. For each, indicate with a "+" or a "—" whether β-galactosidase would be expected to be produced at induced levels. (Assume that glucose is not present in the medium.)
β-galactosidase production
Genotype No Lactose On Lactose
(a) I + O+ Z+/ F' I - O+ Z+ ________ ________
(b) I - Oc Z +/ F'I - O+ Z- ________ ________
(c) I s Oc Z +/ F'I + O+ Z+ ________ ________
(d) I - O+ Z +/ F' I - O+ Z+ ________ ________
I + = wild-type repressor
I - = mutant repressor (unable to bind to the operator)
I s = mutant repressor (insensitive to lactose)
O+ = wild-type operator
Oc = constitutive operator (insensitive to repressor)
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a) -/+
b) -/+
c) +/+
d) +/+
