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Flashcards in Enzymes Deck (14):

Describe cofactors

non-protein component needed for activity


Describe coenzymes

Complex organic molecule, usually formed from vitamins


Describe prosthetic groups

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


Describe apoenzymes

The protein component of an enzyme containing a prosthetic group


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


Define the Michaelis Constant

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


Larger Km values indicate

a less stable ES complex


Lower Km values indicate

a more stable ES complex


Km tells us about

the affinity of the enzyme for the substrate


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


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


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

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


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


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