BSC 315 Lecture Notes - Lecture 21: Dna Binding Site, Lac Repressor, Regulatory Sequence

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silvercicada472

21 Mar 2017

School

University of Alabama

Department

Biological Sciences

Course

BSC 315

Professor

Edwin Stephenson

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Document Summary

Positive regulation of lac gene expression: when is glucose present, expression of the lac operon is turned off. How does lactose turn lac gene expression on and off: normal pattern of lac gene expression is known as inducible , off when lactose is absent, on when lactose is present, lactose is the inducer, occurs via negative regulation. Constitutive mutations: laco- and laci: normal expression: (off when lactose absent; on when lactose present, some mutations cause constitutive expression (assayed easily with onpg or x-gal), constitutive = on all the time, whether lactose is absent or present. If laco- and laci- mutations cause constitutive expression of the lac operon what are the roles of laco+ and laci+: an analogy. The laci gene and laco laci+ gene encodes the lac repressor protein: laci: transcribed independently, and at all times laco+: the operator = dna regulatory sequence to which lac repressor protein binds.

Related Questions

1. What is the term when the product of a biochemical pathway inhibits the activity of the first enzyme of a pathway?

		feedback inhibition.
		activator inhibition.
		diffusional regulation.
		enzyme activation.

2. Through control of gene expression, prokaryotes respond to changing __________ conditions.

		internal
		protein
		environmental
		genetic

3. A protein that negatively regulates transcription by binding to the operator is known as the

		operon
		repressor
		activator
		inducer

4. During attenutation, when tryptophan levels are high, the ________ stem-loop forms and transcription ________ the trpL gene.

		1-2, ends just past
		3-4, ends just past
		1-2, continues beyond
		3-4, continues beyond

5. The process of turning on the expression of a gene in response to a substance in the environment is called:

		constituation.
		repression.
		induction.
		catabolism.

6. What is a function of some specific transcription factors?

		to bind to the promoter region of the gene to facilitate the proper alignment of the RNA polymerase
		to bind to the centromere to induce meiosis
		to bind to enhancer regions to help regulate gene transcription
		to bind to the operator to recruit sigma factor

7. How does exposing an E.coli cell to glucose affect the regulation of the lac operon via CAP?

		cAMP binds to CAP and transcription is increased.
		cAMP binds to CAP and transcription is decreased.
		cAMP does not bind to CAP and transcription is increased.
		cAMP does not bind to CAP and transcription is decreased.

8. The lac repressor protein works when mutations in the repressor gene and structural genes are:

		in cis or in trans.
		in trans only.
		in cis only.
		in both prokaryotes and eukaryotes.

scarletwombat949

When (glucose, lactose) ___________ levels inside a bacterial cell are low, cyclicAMP levels are (high, low) __________. This is because metabolizes sugars (activate, inhibit) ___________ the enzyme adenylate cyclase, and (activate, inhibit) __________ the enzyme cAMP phosphodiesterase, causing cyclic AMP levels to rise. Consequently, the CAP protein is (Activated, inhibited, unaffected) ___________ by the cyclic AMP and binds to the lac promoter region, and the CAP protein acts like a sigma factor recruiting (DNA, RNA) ___________ polymerase to the promoter. This establishes condition that may lead to the (transcription, replication) __________ of the lac operon if (allolactose, glucose, lactose) _____________ is available to bind to (lac repressor, lacZ, lacY, lacA) _________ protein keeping this protein from binding to the (lacO, lacZ. lacY, lacA) ___________ gene.

yellowwasp623

Phosphofructokinase (PFK1) is a glycolytic enzyme that catalyzes the irreversible transfer of a phosphate from ATP to fructose -6-phosphate to form fructose-1, 6- bisphosphate.

fructose-6-phosphate + ATP --> fructose-1,6-bisphosphate + ADP

PFK1 is the key regulatory enzyme for glycolysis. When ATP levels are high in the cell, the cell no longer needs metabolic energy production to occur. In the case of these high energy levels, PFK1's activity is inhibited by allosteric regulation by ATP, which essentially closes the valve on the flow of carbohydrates through glycolysis.

Recall that allosteric regulators bind to a different site on the enzyme rather than the active (catalytic) site. ATP binds to the regulatory site and decreases PFK1 activity. ATP bound in the regulatory site acts as a modulator by lowering the affinity of PFK1 for its substrate, fructose-6-phosphate. AMP on the other hand, which is generated when the cell is in a low energy state binds to allosteric site and increases enzyme activity.

7. The enzyme PFK1 is an example of a non-regulatory enzyme or regulatory enzyme?

8. How is PFK regulated?

A. It is not regulated because it is a non-regulatory enzyme

B. allosteric enzyme regulation

C. covalent enzyme regulation

D. or proteolytic cleavage enzyme regulation?

9. What is the substrate and to which site on the enzyme does it bind? Which compounds are the positive and negative effectors?

10. In which conformational state would the enzyme be when negative inhibitors bind and in which conformational state would the enzyme be when positive inhibitors bind?

11. PFK1 is a heterotropic or homotropic regulatory enzyme?

12. Draw (or insert the picture from your course packet available on Canvas) the graph that corresponds to this reaction. Your graph should include the activity of PFK without bound effectors, with bound positive effector, and with bound negative effector. Label (or describe) each line to distinguish these along with which molecules are positive and negative effectors.

13. How does Vmax and K0.5 change with the positive and negative effectors?

BSC 315 Lecture Notes - Lecture 21: Dna Binding Site, Lac Repressor, Regulatory Sequence

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