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BIO 2 > CONTROL OF GENE EXPRESSION IN PROKARYOTES (LECTURE 8) > Flashcards

CONTROL OF GENE EXPRESSION IN PROKARYOTES (LECTURE 8) Flashcards

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1
Q

For the regulation of metabolic pathways, there is regulation occurring at what 2 levels?

A

(1) Regulation at the protein level (negative feedback inhibition) and (2) regulation at the gene level.

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2
Q

How are prokaryotic genes organized?

A

Prokaryotic genes are organized into operons.

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3
Q

What can be said about genes within the same operon?

A

Operons contain genes that code for proteins (mostly enzymes) that function in the same metabolic pathway.

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4
Q

What are the two elements of an operon?

A

The promotor and the genes.

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5
Q

Describe the promoter of an operon.

A

Promoters contain an on/off switch called the operator.

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6
Q

The genes in an operon are controlled by the same what?

A

By the same operator within the promoter of that operon.

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7
Q

Since the genes of an operon share a promoter, what can be said about the product of their transcription?

A

They are transcribed as one single mRNA molecule.

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8
Q

Although the genes within an operon are transcribed as one single mRNA molecule, each gene has its own what?

A

Each gene has its own start and stop codon for translation of each polypeptide.

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9
Q

Describe the activity of prokaryotic DNA within an operon when that operon is turned on.

A

RNA polymerase binds to the promoter, all genes of the operon are transcribed as one long mRNA and each gene on the mRNA is translated into a polypeptide.

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10
Q

Describe the activity of prokaryotic DNA within an operon when that operon is turned off.

A

A repressor protein binds to the operator, preventing RNA polymerase from binding to the promoter and thus transcription is blocked.

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11
Q

What is a repressor protein?

A

A protein that binds to an operator to turn off the operon containing that operator.

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12
Q

The repressor protein is the product of what?

A

Of a regulatory gene.

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13
Q

Describe the regulatory gene that codes for the repressor protein of an operon.

A

The regulatory gene is located upstream (5’) of the operon promoter and the gene is always being transcribed.

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14
Q

The binding of repressor to operator is ____.

A

The binding of repressor to operator is reversible.

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15
Q

Can repressor proteins be regulated? By what?

A

Repressor proteins can be regulated by allosteric regulators.

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16
Q

Where do allosteric regulators bind to on a repressor protein?

A

On the repressor protein’s allosteric site.

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17
Q

Allosteric regulators are _____ in the cell.

A

Allosteric regulators are metabolites in the cell.

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18
Q

Provide two examples of metabolites that function as allosteric regulators.

A

Tryptophan and allolactose.

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19
Q

What difference is there between an active repressor and an inactive repressor protein?

A

An active repressor protein can bind to the operator, an inactive repressor protein cannot.

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20
Q

Operons can be ____ or ____.

A

Operons can be repressible or inducible.

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21
Q

Repressible operons are ____ by default.

A

Repressible operons are on by default.

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22
Q

Inducible operons are ____ by default.

A

Inducible operons are off by default.

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23
Q

Describe the regulation of transcription in repressible operons.

A

Transcription is turned off by the product of a metabolic pathway.

24
Q

Provide an example of a repressible operon.

A

The Trp operon.

25
Q

Describe the regulation of transcription in inducible operons.

A

Transcription is turned on by the presence of a reactant in a metabolic pathway.

26
Q

Provide an example of an inducible operon.

A

The Lac operon.

27
Q

Describe the trp operon (repressible).

A

It codes for enzymes involved in the production of tryptophan. Repressor protein is active when bound to tryptophan - tryptophan is a corepressor.

28
Q

Describe the activity of the trp operon in low tryptophan concentration.

A

The repressor protein is inactive and does not bind to the operator. Operon is turned on and mRNA is produced.

29
Q

Describe the activity of the trp operon in high tryptophan concentration.

A

Repressor protein is active and binds to the operator. Operon is turned off and mRNA is not produced.

30
Q

Describe the state of transcription in the trp operon in high versus low concentrations of tryptophan.

A

In high concentrations, transcription is off. In low concentrations, transcription is on.

31
Q

Describe the lac operon (inducible).

A

Produces enzymes involved in lactose metabolism (breaking down lactose for energy). Repressor protein is inactive when lactose is present - allolactose acts as an inducer (lactose is converted into allolactose in the cell).

32
Q

Describe the activity of the lac operon when lactose is not present.

A

Repressor protein is active and binds to the operator. Operon is turned off.

33
Q

Describe the activity of the lac operon when lactose is present.

A

Allolactose binds to repressor and inactivates it. Repressor protein is inactive and does not bind to operator. Operon is turned on and mRNA is produced.

34
Q

The control of gene expression can either be ____ or ____.

A

The control of gene expression can either be positive or negative.

35
Q

Describe positive control of gene expression.

A

Positive control is when transcription can be increased by an activator.

36
Q

Provide an example of positive control of gene expression.

A

CAP-CAMP is an activator for the lac operon.

37
Q

Describe negative control of gene expression.

A

Negative control is when the operon can be turned off by a repressor protein, which is the case for both repressible and inducible operons.

38
Q

Provide 2 examples of negative control of gene expression.

A

Trp operon and lac operon both have repressor proteins that can turn off transcription.

39
Q

Even when lactose is present, what can cause transcription levels of the lac operon to be very low?

A

High glucose concentration can cause lac operon transcription levels to be very low despite the presence of lactose.

40
Q

Why does a high concentration of glucose decrease transcription levels of the lac operon?

A

Because glucose is a better energy source than lactose, so there is no point is breaking down lactose when glucose is present.

41
Q

In addition to an operator, what else is located on the lac operon promoter?

A

The lac operon promoter also has a CAP - binding site.

42
Q

What must bind to the lac operon promoter to stimulate transcription?

A

Active CAP binds to the promoter to stimulate transcription of the lac operon.

43
Q

When is CAP in its active conformation?

A

When bound by cyclic AMP (cAMP).

44
Q

When are cAMP levels high?

A

When glucose levels are low.

45
Q

Glucose acts as an inhibitor to what what enzyme?

A

Glucose inactivates / inhibits adenylyl cyclase.

46
Q

What chemical reaction is catalyzed by adenylyl cyclase (or just adenyl cyclase)?

A

ATP –> cAMP

47
Q

Describe, step by step, how low glucose concentrations increase the transcription levels of the lac operon.

A

low [glucose] –> high [cAMP] –> Active CAP –> CAP binds to promoter –> transcription increases!

48
Q

Describe, step by step, how high glucose concentrations decrease the transcription levels of the lac operon.

A

High [glucose] –> low [cAMP] –> Inactive CAP –> CAP leaves promoter –> transcription decreases.

49
Q

Will transcription be turned on if there is no glucose but no lactose in the cell?

A

No.

50
Q

When transcription of an operon is on, this means the repressor is ____ and ____.

A

When transcription of an operon is on, this means the repressor is inactive and not bound.

51
Q

When transcription of an operon is off, this means the repressor is ____ and ____.

A

When transcription of an operon is off, this means the repressor is active and bound.

52
Q

The lac operon is ____ in the presence of lactose.

A

The lac operon is on in the presence of lactose.

53
Q

The lac operon is ____ when no lactose is present.

A

The lac operon is off when no lactose is present.

54
Q

The trp operon is ____ in the presence of trp.

A

The trp operon is off in the presence of trp.

55
Q

The trp operon is ____ when no trp is present.

A

The trp operon is on when no trp is present.

BIO 2 (14 decks)

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