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PHS2102 > Lecture 7: enzymes > Flashcards

Lecture 7: enzymes Flashcards

1
Q

What happens during acid base catalysis?

A

The amino acid side chain donates or accepts protons to the substrate to form the product

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2
Q

What happens during covalent catalysis?

A
  1. The amino acid at the active site mounts a nucleophilic attack on the electrophilic site on the substrate
  2. This forms a transient covalent bond between the enzyme and the substrate, which lowers the activation energy
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3
Q

What happens during metal ion catalysis?

A

Metal ions act as cofactors for the enzyme
They can:
1. Bind to substrates and orientate it in an optimal spatial arrangement
2. Mediate oxidation reduction reactions
3. Stabilise or shield negative charges

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4
Q

What are the categories of enzyme cofactors?

A
  1. Prosthetic cofactors: tightly bound to the enzyme
  2. Coenzymes/co-substrates: loosely bound to the enzyme
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5
Q

What are the major classes of enzymes and what kind of reaction do they catalyse?

A
  1. Oxidoreductases: Redox reaction
  2. Transferases: move chemical groups
  3. Hydrolases: hydrolysis
  4. Lyases: non-hydrolytic bond cleavage
  5. Isomerases: intramolecular group transfer (isomerization)
  6. Ligases: Synthesis of new covalent bond between substrates
  7. Translocases: Catalyse the movement of ions or molecules across membranes
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6
Q

How to calculate rate of reaction?

A

v = (Vmax x [S]) / (Km + S)

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7
Q

What happens to the rate of reaction when the Michaelis constant is equal to the substrate concentration?

A

V = 0.5Vmax

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8
Q

What is Kcat?

A
  1. Turnover number
  2. Measures the maximum number of substrate molecules converted to product per unit time per active site
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9
Q

How do you calculate Kcat?

A

Kcat = Vmax / [E]T

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10
Q

What is the specificity constant and how do you calculate it?

A
  1. It measures the specificity of the enzyme for the substrate
  2. An overall measure of enzyme efficiency
  3. specificity constant = Kcat/Km
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11
Q

What do you get when you linearize a Michalis Menten plot?

A

Lineweaver-Burk plot

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12
Q

What is the lineweaver burk equation?

A

1/V = (Km/Vmax) / 1/[S] + 1/Vmax

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13
Q

How does a reversible competitive inhibitor work?

A
  1. The inhibitor is structurally similar to the substrate
  2. It competes with the substrate for binding to the active site
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14
Q

Are Vmax and Km affected by a competitive inhibitor?

A

Vmax no
Km increases (affinity decreases)

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15
Q

Can competitive inhibition be overcome?

A

Yes, by increasing substrate concentration

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16
Q

What is inhibitory constant?

A
  1. It is the concentration of the inhibitor required to occupy 50% of the enzyme’s active site
17
Q

How does a non competitive inhibitor work?

A
  1. It binds to the allosteric site
  2. It can bind to the enzyme or the enzyme substrate complex to prevent the reaction from occuring
18
Q

What happens to an enzyme’s Km and Vmax in the presence of a non-competitive inhibitor?

A

Km is unchanged
Vmax decreases

19
Q

How do you calculate the observed Vmax in the presence of a non-competitive inhibitor?

A

Vmax (observed) = Vmax (original) / (1 + [I]/Ki)

20
Q

How do you calculate the rate of reaction of an enzyme in the presence of a non-competitive inhibitor?

A

V = Vmax[S] / (Km + [S])(1 + [I]/Ki)

21
Q

How does uncompetitive inhibition work?

A
  1. Inhibitor binds to ES complex
  2. It alters the way the ES complex would dissociate to release the product or the way the substrate binds to the enzyme
22
Q

What happens to an enzyme’s Km and Vmax in the presence of a uncompetitive inhibitor?

A

Km decreases
Vmax decreases

23
Q

Why does Vmax decrease when using a uncompetitive inhibitor?

A

When substrate concentration increases, more inhibitor molecules bind to the ES complex

24
Q

Why does Vmax decrease when using a non-competitive inhibitor?

A

Inhibition cannot be overcome by increasing substrate concentration

25
Q

Are irreversible inhibitors competitive or non competitive?

A

Can be both

26
Q

What happens during irreversible inhibition?

A
  1. A covalent bond is formed between the inhibitor and the active/allosteric site of the enzyme
  2. Permanently stops the catalysis, the restoration of enzymatic activity can only be done by synthesizing new enzymes
27
Q

What are the main clinical uses of enzymes?

A
  1. As therapeutics
  2. As key components in diagnostic/analytical assays
28
Q

When is enzyme replacement therapy used?

A

Used on patients with defective or aberrant enzyme activity in metabolic pathways

29
Q

What is K1?

A

The forward rate constant (formation of ES complex)

30
Q

What is K2?

A

The rate constant of the breakdown of ES into enzyme and product

31
Q

What is K-1?

A

The rate constant of the dissociation of ES into enzyme and substrate

32
Q

How do you calculate Km using K2, K1 and K-1 values?

A

Km = (K2 + K-1) / K1

PHS2102 (15 decks)

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