Enzymes Flashcards Preview

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Flashcards in Enzymes Deck (14):
1

Describe cofactors

non-protein component needed for activity

2

Describe coenzymes

Complex organic molecule, usually formed from vitamins

3

Describe prosthetic groups

Cofactor covalently bound to the enzyme or very tightly associated with the enzyme

4

Describe apoenzymes

The protein component of an enzyme containing a prosthetic group

5

Give three ways in which enzymes catalyse reactions

- increase rate of spontaneous reactions
- lower the activation energy of biochemical reactions
- accelerate movement toward reaction equilibria

6

Define the Michaelis Constant

Km = 1/2 Vmax = k.1 + k2/k1

7

Larger Km values indicate

a less stable ES complex

8

Lower Km values indicate

a more stable ES complex

9

Km tells us about

the affinity of the enzyme for the substrate

10

Describe competitive inhibition

- these inhibitors bind to enzymes in the same way as the intended substrate
- bind non-covalently and tend to resemble proper substrate
- leads to increase in Km as affinity for proper substrate decreases
- increasing conc. of substrate can displace the competitor and Vmax can be achieved

11

Describe non-competitive inhibition

- these inhibitors bind non-covalently
- bind to a site other than the active site of the enzyme
- enzyme can still bind to active site so Km is unchanged
- inhibitor cannot be displaced by increasing conc. of substrate so Vmax will decrease

12

Metabolites can bind to allosteric sites on some enzymes to act as

inhibitors or activators
- this is an example of non-competitive inhibition

13

Describe the concerted model

- each subunit can exist in 2 different confirmations
- one will have low Km, other will have high Km
- with no substrate, enzyme flips between conformations
- all units must be the same conformation i.e. in concert
- when 1 substrate binds it holds enzyme in open conformation
- increases affinity and explains sigmoid curve

14

Describe the sequential model

- no flipping between different conformational states
- binding causes a conformation change in 1 subunit
- this causes a change in another subunit making further binding easier
- binding sensitises the enzyme to more substrate