Enzymes

Question 1

major classes of enzymes

Answer 1

oxidoreductases
transferases
hydrolases
lyases
isomerases
ligases

Question 2

oxidoreductases

Answer 2

catalyse redox reactions

Question 3

transferases

Answer 3

transfer functional groups between donors and acceptors

Question 4

hydrolases

Answer 4

catalyse hydrolysis

Question 5

lyases

Answer 5

catalyse removal of group, not by hydrolysis or oxidation

Question 6

isomerases

Answer 6

catalyse intermolecular rearrangement

Question 7

ligases

Answer 7

catalyse union of 2 molecules

Question 8

exergonic

Answer 8

products more stable than reactants

Question 9

key concept of delta G

Answer 9

independent of path taken

Question 10

free energy at equilibrium

Answer 10

0
no net change in concentration of reactants or products

Question 11

how do enzymes work

Answer 11

lower activation energy of transition state by stabilising it to make its gibbs free energy lower

Question 12

delta G dagger

Answer 12

difference in free energy between the transition state and the substrate

Question 13

what type of interactions form between the enzyme and the substrate and binding energy

Answer 13

non covalent
releases some energy that stabilises the interaction: binding energy

Question 14

in induced fit, what are the enzymes actually complementary to

Answer 14

the transition state

Question 15

rearrangement of covalent bonds by enzymes

Answer 15

makes carbonyl more electrophilic so water is a strong enough nucleophile to make tetrahedral intermediate

Question 16

catalytic triad

Answer 16

3 amino acids that interact with each other in the active site of protease to increase the nucleophilicity (ability of an atom to donate a pair of electrons to form a new covalent bond in a reaction) of the serine residue
The histidine is a base, so accepts the hydrogen, giving the oxygen a negative charge. This makes it a strong enough nucleophile to attack the carbonyl and form the tetrahedral intermediate. Electrons move back down and the double bond is reformed, which kicks out the blue section. The peptide has been cleaved but the red section is still covalently bonded to the serine residue. The serine residue has been acylated as an ester has been formed. The red section is now a better electrophile. The histidine in the catalytic triad can deprotonate a water molecule, and OH- is now a good enough nucleophile to attack the carbonyl to form another tetrahedral intermediate. The electrons move back down to reform the double bond and kicks out the serine. Product is formed and catalytic triad is reformed.

Question 17

4 things enzymes do

Answer 17

release binding energy by forming non covalent interactions
rearrange covalent bonds
hold reactants and products close together in the necessary orientation
cause desolvation of substrate