enzymes

Question 1

substrate binding site [active site]

Answer 1

• substrates bind to specific sites through interactions with amino acids, coenzymes, metal ions. spatial geometry dictates specificity

Question 2

activation energy and transition sites

Answer 2

binding of substrates promotes formation of a transition state which lowers the activation energy

Question 3

catalytic cycle

Answer 3

1) substrate binds
2) product formed
3) product unbinds

Question 4

lock and key model

Answer 4

• complementary 3D surface recognises substrate
• substrate binds through H-bonds, hydrophobic and electrostatic interactions
• binding can be prevented by steric hindrance and charge repulsion

Question 5

induced fit model

Answer 5

• as substrates bind, enzymes undergo a conformational change
• side chains of active amino acids reposition
• binding interactions increase
• not a rigid lock, but a dynamic surface

Question 6

the transition state complex

Answer 6

• the transition state is the point of maximal bond strain
• activation energy is the free energy difference between substrate and transition state complex
• overall rate of reaction is determined by overall number of molecules acquiring the AE.

Question 7

cofactors/coenzymes

Answer 7

• catalytic properties and often dependent on non-peptide molecules called cofactors- metal ions and organic enzymes. tightly bound cofactors are known as prosthetic group. in humans coenzymes are usually synthesised from vitamins

Question 8

cofactors: metal ions

Answer 8

positively charged metal ions act as electrophiles- assist in substrate binding or stabilise anions. can acceot or even donate electrons in redox reactions

Question 9

isoenzymes

Answer 9

enzymes that differ in sequence (ie. different genes) but catalyses the same reaction. they can have different kinetic parameters and substrate specificities.

Question 10

multiple enzyme complexes

Answer 10

some enzymes catalysing multiple consecutive steps in metabolic pathways associate to form multi-enzyme complexes

Question 11

diagnostic enzymology

Answer 11

measurement of enzyme activity/concentration, can include serum enzymes, secreted enzymes and enzymes released by damaged/malignant cells. cell leakage can be caused by reduced oxygen, toxuc chemicals, microorganisma, immune responses, genetic conditions. released enzymes are affected by metabolism and excretion, they therefore have different serum half-lives

Question 12

Vo

Answer 12

initial rate of enzyme activity

Question 13

[S]

Answer 13

substrate concentration

Question 14

Vmax

Answer 14

the maximum possible rate at that enzyme

the Vmax is directly proportional to the amount of enzyme used

Question 15

Km (michaelis constant)

Answer 15

the [S] resulting from Vmax/2 (divided by 2)

• enzyme velocity is most sensitive to changes in [S] close to Km.
• if Km is shown, the [S] required to saturate the enzyme can be calculated.
• high Km= low substrate efficacy and vice versa