Enzyme Catalysis Flashcards

1
Q

What is general base catalysis?

A

Partial proton abstraction from a Bronsted base.

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2
Q

Why is acid/base catalysis useful?

A

It helps the enzyme to stabilise charged intermediates during the reaction.

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3
Q

What is specific acid-base catalysis?

A

Catalysis involving protons or OH ions specifically.

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4
Q

What is concerted acid-base catalysis?

A

When both processes occur simultaneously.

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5
Q

What does covalent catalysis involve?

A
  1. Nucleophilic reaction between the catalyst and the substrate to form a covalent bond.
  2. Withdrawal of electrons from the reaction centre by the now electrophilic catalyst.
  3. Elimination of the catalyst.
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6
Q

What is limiting the rate of reaction in nucleophilic catalysis?

A

Covalent bond formation.

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7
Q

What is limiting the rate of reaction during electrophilic catalysis?

A

Withdrawal of electrons.

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8
Q

How is a schiff base formed?

A

Condensation of an amine with a carbonyl compound.

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9
Q

How does a schiff base act as an electron sink?

A

The positive N atom stabilises any negative charge on an adjacent carbon.

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10
Q

What is a good covalent catalyst?

A

A group with high nucleophilicity and the ability to form a good leaving group.

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11
Q

Give examples of coenzymes usually involved in covalent catalysis.

A

Thiamine pyrophosphate and pyridoxal phosphate.

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12
Q

What are metalloenzymes?

A

Enzymes with tightly bound metal ions.

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13
Q

What are metal-activated enzymes?

A

Enzymes that loosely bind metal ions from solution.

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14
Q

How is metal ion catalysis useful?

A
  • metal ions bind to substrates and orientate them properly.
  • metal ions facilitate redox reactions through changes in the metal’s oxidation state
  • metal ions stabilise charges
  • metal ions shield charges
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15
Q

How do metal ions stabilise charges?

A

By acting as Lewis acids.

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16
Q

How can water be made a better nucleophile?

A
  • by abstracting a proton

- by binding a metal ion

17
Q

What is electrostatic catalysis?

A

Enzymes arrange active site charge distributions in order to stabilise the transition state.

18
Q

What effect do proximity and orientation have on catalysis?

A

Reactants must come together with the proper spatial relationship for a reaction to occur.

19
Q

When are molecules maximally reactive?

A

When their orbitals are aligned so that the electronic energy of the transition state is minimised.

20
Q

What is general acid catalysis?

A

Partial proton transfer from a Bronsted acid.

21
Q

What are the features of a perfectly evolved enzyme?

A

Diffusion controlled. Km is much higher than physiological [S] value.