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Biochem 2 > Lecture 16 - Regulation > Flashcards

Lecture 16 - Regulation Flashcards

1
Q

What is an example of short term regulation?

A

Feedback inhibition (and activation)

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2
Q

What is an example of post-translational control?

A

Protein kinase and protein phosphatase in glycogen metabolism control by covalent modification (+/- phosphate)

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3
Q

What is an example of long term control?

A

Control of RNA and protein levels because the response time is longer

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4
Q

What is an example of compartmentation regulation?

A

Beta-oxidation occurs inside the mitochondria, whereas fatty acid synthesis occurs in the cytoplasm

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5
Q

What is an example of hormonal regulation?

A

Glycogen regulation

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6
Q

How are branched pathways regulated?

A

1) Multiple enzyme control
2) Sequential control
3) Synergistic feedback

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7
Q

Describe multiple enzyme control

A

Multiple alleles of the same enzyme (1 and 2) catalyze a step early in the pathway, and are affected differently by different inhibitors (E and G)

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8
Q

What is the problem with multiple enzyme control?

A

Additional sites of control are required in each branch after the initial branch point

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9
Q

Describe sequential control

A

The end products inhibit a step after the branch, which causes a build-up of an intermediate, which in turn acts sequentially to inhibit a step earlier in the pathway

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10
Q

Describe synergistic feedback

A
  • 2 end products work synergistically to inhibit a step early in the pathway and together have a much larger effect than individually
  • Can be cumulative (effects of E and G are additive) or concerted (neither has an effect individually)
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11
Q

What does control of transcription affect?

A

The number of mRNA molecules produced, thereby affecting the number of protein (enzyme) molecules produced

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12
Q

Is transcriptional control common? Why or why not?

A

Yes because it provides greater energy efficiency in stopping both RNA and protein synthesis

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13
Q

What is an operon?

A

A grouping of genes, the products of which have a common metabolic purpose

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14
Q

What is the function of lac operon?

A

Metabolism of lactose (galactose-beta1,4-glucose)

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15
Q

What does lac operon encode?

A
  • Transport protein (lactose permease) to transport lactose into the cell
  • Cleavage enzyme (beta-galactosidase) to cleave the 2 sugars
  • Beta-galactoside transacetylase for detoxification
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16
Q

Which reactions does beta-galactosidase catalyze?

A

1) Lactose galactose + glucose

2) Galactose + glucose allolactose

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17
Q

What affects the synthesis of beta-galactosidase mRNA?

A

The carbon sources present in the growth medium

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18
Q

When is beta-galactosidase produced?

A

When substrate is present

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19
Q

Is lac operon produced when succinate is present?

A

No

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20
Q

Is lac operon activated when lactose is present?

A

Yes, to digest the lactose

21
Q

Is lac operon activated when glucose is added?

A

No, because glucose is a better substrate than lactose, so beta-galactosidase isn’t required

22
Q

What are the 3 states of lac operon?

A

1) Repressed
2) Induced
3) Catabolite repressed

23
Q

When is lac operon repressed?

A

When succinate is the carbon source

24
Q

When is lac operon induced?

A

When lactose is present in the medium

25
Q

When is lac operon catabolite repressed?

A

When glucose is in the medium

26
Q

What does the I gene of lac operon do?

A

Encodes repressor protein

27
Q

What does the Pi gene of lac operon do?

A

Promotes the I gene

28
Q

What does the P gene of lac operon do?

A

Promotes the lac gene

29
Q

What does the Z gene of lac operon do?

A

Encodes beta-galactosidase

30
Q

What does the Y gene of lac operon do?

A

Encodes galactosidase permease

31
Q

What does the A gene of lac operon do?

A

Encodes transacetylase

32
Q

What does the O1 gene of lac operon do?

A

Main operator for the lac operon

33
Q

Which genes of lac operon are the regulatory system?

A

I, O, and P

34
Q

Which genes of lac operon are the structural genes?

A

Z, Y, and A

35
Q

What does the crp gene encode? Is it linked to the lac operon?

A
  • Encodes a transcription activator protein known as catabolite gene activator protein (CAP) or cAMP receptor protein (CRP)
  • Not linked
36
Q

What does CAP require for activity?

A

cAMP

37
Q

What occurs in the repressed state of lac operon?

A

The repressor binds to the operator, which overlaps the promoter and prevents RNA polymerase and CAP from binding

38
Q

What occurs in the induced state of lac operon?

A
  • CAP-cAMP facilitates RNA-P binding to the promoter, which activates transcription
  • Repressor is bound by allolactose
39
Q

How does allolactose inhibit the repressor?

A

It brings the equilibrium of the repressor closer to the T (inactive) state

40
Q

What occurs in the catabolite repressed state of lac operon?

A
  • Glucose causes cAMP levels to drop, reducing the amount of CAP-cAMP
  • Repressor is inactive because of the presence of lactose/allolactose
41
Q

Is lac operon a catabolic or anabolic operon and why?

A
  • Catabolic

- Only turned on when the substrate of the operon is present so energy is not wasted

42
Q

Is trp operon a catabolic or anabolic operon and why?

A
  • Anabolic

- Turned off when the product of the operon enzymes is present so that energy is not wasted

43
Q

When is the trp operon induced?

A

When glucose is present as a substrate and no tryptophan is present

44
Q

When is the trp operon repressed?

A

When tryptophan is added (no need to produce more)

45
Q

How does the trp operon become repressed?

A

Tryptophan binds to the repressor protein, which binds to the operator, blocking the mRNA from the tryptophan synthetic enzymes

46
Q

What are 2 examples of multiple feedback inhibition?

A

1) Threonine and methionine inhibit homoserine dehydrogenase

2) Threonine, homoserine, and isoleucine inhibiti aspartate kinases

47
Q

What is an example of sequential feedback inhibition?

A

Isoleucine blocks threonine, which blocks homoserin

48
Q

What is an example of synergistic feedback inhibition?

A

Isoleucine and lysine together inhibit aspartate semialdehyde

49
Q

What are 2 examples of long term transcriptional control in the isoleucine synthesis pathway?

A

1) Threonine and isoleucine are corepressors of the operon with genes encoding aspartyl kinase 1 and homoserine dehydrogenase 2
2) Methionine is a corepressor of the operon with genes encoding aspartyl kinase 2 and homoserine dehydrogenase 1

Biochem 2 (40 decks)

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