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Biochem > Enzyme Regulation > Flashcards

Enzyme Regulation Flashcards

1
Q

Multiple steps in metabolic pathways allow

A

Efficient energy utilization

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2
Q

What do interconnections in metabolic pathways ensure?

A

Efficient utilization of metabolites

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3
Q

What are reversible reactions controlled by?

A

Changes in substrate

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4
Q

Irreversible reactions are…

A

Enzyme regulated

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5
Q

What is flux?

A

The rate at which the starting material is converted to the products of the pathway

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6
Q

What are 3 ways flux is controlled through a pathway?

A
  1. Enzymes in the pathway
  2. Supply of starting material
  3. Rate of product utilization
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7
Q

Flux through a pathway is never faster than what?

A

The rate limiting step

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8
Q

What is feedback regulation?

A

When the product of a pathway controls its synthesis

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9
Q

2 types of feedback regulation

A
  1. Product inhibition
  2. Feedback inhibition
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10
Q

List 5 factors involved in regulation of enzyme activity

A
  1. Substrate conc
  2. Product inhibition vs Feedback inhibition
  3. Allosteric activation and inhibition
  4. Cooperativity
  5. Post-translational modification
    Phosphorylation/dephosphorylation
    Proteolysis to activate an inactive precursor called
    a zymogen
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11
Q

For many enzymes, where is [S]?

A

Near Km

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12
Q

When [S]&raquo_space;Km, the rxn velocity…

A

Doesn’t change with [S]

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13
Q

When [S] &laquo_space;Km, the rxn velocity…

A

Changes in proportion to [S]

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14
Q

According to the Michaelis-Menter Equation, how much change in substrate conc is necessary to access the full dynamic range of enzyme initial velocity?

A

~100 fold

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15
Q

What is product inhibition?

A

When the product of an enzyme inhibits that enzyme

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16
Q

What is feedback inhibition?

A

When the product of a metabolic pathway influences its production

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17
Q

What two isozymes are controlled by different mechanisms?

A

Hexokinase and glucokinase

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18
Q

Does hexokinase have high/low Km?

A

Low Km

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19
Q

What is hexokinase inhibited by?

A

Its product glucose-6-P

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20
Q

Does glucokinase have high/low Km?

A

High Km

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21
Q

What is glucokinase regulated by?

A

Conc of glucose, making it a “glucose sensor”

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22
Q

Whaat is allostery?

A

Process by which biological macromolecules transmit effect of binding at one site to an often distal, functional site, allowing for regulation of activity

23
Q

What 2 things does allostery require?

A
  1. Binding
  2. Change in conformation associated with binding
24
Q

What can allostery result in?

A

Activation or inhibition/positive or negative feedback

25
Q

Allosteric enzymes have ___ and ___ affinity conformations

A

low and high

26
Q

What does cooperativity apply to?

A

Multimeric enzymes En with n equivalent active sites

27
Q

What are homotropic allosteric modifiers?

A

substrates for the active site

28
Q

What are heterotropic allosteric modifiers?

A

Do not bind at active site; not substrates

29
Q

Heterotropic allosteric modifiers differ from…

A

Ligand at active site

30
Q

Heterotropic inhibitors stabilize a ___ affinity form of the active site

A

low

31
Q

Heterotropic activators stabilize a ____ affinity form of the active site

A

high

32
Q

What does PFK-1 do?

A

Incorporates phosphate from ATP into F6P to form F16BP

33
Q

What shape is the graph of PFK-1 velocity vs F6P substrate?

A

Sigmoidal - signature of + cooperativity

34
Q

PFK-1 has ___ identical subunits, each with 1 active site

A

4

35
Q

In the absence of substrate F6P, PFK-1 exists in the ___-state

A

T

36
Q

When F6P binds at 1 active site, all other sites…

A

Switch to high affinity R-state

37
Q

F6P is a…

A

homotropic allosteric activator

38
Q

ATP is what 2 things?

A
  1. Substrate
  2. Heterotropic inhibitor
39
Q

PFK-1 has what 2 different ATP binding sites on each subunit?

A
  1. 1 ATP site is active site (where ATP is substrate)
  2. Other ATP site is not active site, it stabilizes low affinity T-state for F6P
40
Q

F26BP is a….

A

Heterotropic activator

41
Q

F26BP activates…

A

PFK-1

42
Q

Where does F26BP not bind?

A

Active site of PFK-1/ Heterotropic allosteric activator

43
Q

What enzymes do phosphorylation/dephos. and on what residues?

A

Kinases do phosphorylation/dephosphorylation of serine, threonine, or tyrosine residues

44
Q

What enzymes do proteolysis that activate a precursor (zymogen/proenzyme)?

A

Proteases

45
Q

Protein kinases transfer… to hydroxyl groups of…

A

Protein kinases transger phosphate from ATP (NTP) to hydroxyl groups of ser, thr, tyr

46
Q

What do protein phosphatases do?

A

Remove phosphate from the enzyme

47
Q

AMP is a …. of ….

A

AMP is a heterotropic allosteric activator of glycogen phosphorylase

48
Q

High AMP in ___ cell

A

High AMP in a low energy cell

49
Q

What further stabilizes glycogen phosphorylase active form?

A

Phosphorylation

50
Q

Which of many enzymes are translated as inactive zymogens and activated by proteolysis?

A

Pancreatic digestive enzymes

51
Q

What is the blood clotting cascade controlled by?

A

Proteolytic activation of inactive proteases (zymogens)

52
Q

What converts prothrombin to thrombin?

A

Factor Xa

53
Q

What is prothrombin?

A

An inactive protease (zymogen)

54
Q

What is thrombin?

A

An active protease?

Biochem (6 decks)

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