Protein Function: Catalysis Flashcards

Lecture 6

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1
Q

What does a catalyst do?

A

Increases the rate of reaction by lowering the activation energy barrier in the absence of thermal activation

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2
Q

Why don’t reactions occur instantaneously?

A

Provides an opportunity for regulation; also, reactions in cells are steady state

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3
Q

Does a catalyst influence the rate of the reaction?

A

Yes

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4
Q

Does a catalyst influence the position of equilibrium of a reaction?

A

No.

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5
Q

Describe the slope of the rate of a reaction and the concentration of a reagent without an enzyme catalyst.

A

Linear slope

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6
Q

Describe the slope of the rate of a reaction and the concentration of a reagent with an enzyme catalyst.

A

Hyperbolic slope, no longer linear

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7
Q

Why would a reaction’s rate plateau when using enzymes in vitro?

A

If the enzymes become saturated with substrates, then they’re all occupied and can not increase the rate any more.

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8
Q

What’s the first step of catalysis?

A

Substrate binding

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9
Q

How does a catalyst act?

A

Forms a reversible complex with a substrate, stabilizing a transition state

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10
Q

What does folding the catalyst do?

A

Creates a binding site where specific R groups are presented to each other; specific topology allows enzymes to have specificity.

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11
Q

Is Vmax ever reached?

A

No, it is only approached.

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12
Q

What is Vmax proportional to?

A

the concentration of enzymes

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13
Q

What is Vmax?

A

maximum velocity of a reaction, when 100% of the enzymes are bound to a substrate

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14
Q

What determines the initial rate of an enzyme catalyzed reaction?

A

Km, Vmax, and the initial substrate concentration

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15
Q

What does Vmax tell us?

A
  1. At high [S], reaction rates vary significantly among different enzymes.
  2. Allows a calculation of kcat (the turnover number of a specific enzyme - measures how effective an enzyme is)
  3. In vivo, few enzymes encounter saturating [S]; Vmax and kcat set upper bounds, enabling estimates of reaction rates in vivo.
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16
Q

What does Km (Michaelis Constant) tell us?

A

measure of affinity of enzyme for substrate

17
Q

What does a high Km indicate?

A

low affinity for a substrate, may require higher substrate concentration for a reaction in vivo

18
Q

What does a low Km indicate?

A

high affinity for a substrate, may not require higher substrate concentration for a reaction in vivo

19
Q

What are the four kinds of enzyme regulation?

A
  1. Substrate-Level
  2. Covalent Modification (e.g. phosphorylation of Cdk)
  3. Modulator Proteins
  4. Allosteric
20
Q

What do modulator proteins do?

A

Bind to enzymes and either stimulate or deactivate them

21
Q

What is an allosteric effector?

A

a small molecule that regulates
the activity of an enzyme for which it is neither substrate nor immediate product

22
Q

Which kind of enzyme regulation does not obey Michaelis-Menten equation?

A

Allosteric

23
Q

How does temperature relate to the rate of the reaction? What is the rule of thumb?

A

Increased temperature increases the rate. For every 10 degrees C increase, the rate doubles (until max activity).

24
Q

Why are enzymes impacted by pH?

A

Many active sites have charged amino acid side chains and are ionizable.

25
Q

What influence does diffusion have on catalysis involving multiple enzymes?

A

Reduces the efficiency of metabolic reactions requiring multiple enzymes

26
Q

Can temperature impact pH?

A

Yes

27
Q

Can saturation occur in the cell?

A

No, only in vitro.

28
Q
A