lecture 43 - general catalysis mechanisms

Question 1

generally, what are two ways in which the rate of reaction can be increased?

Answer 1

(1) provide energy to the system (heat - allows molecules to collide with more energy)
(2) lower energy of the transition state (I.e. reducing the activation energy)

Question 2

explain the gibbs free energy graph for an enzyme catalyzed reaction

Answer 2

3 part graph - overall is less energy than the uncatalyzed

part 1: E + S –> ES

• endergonic reaction (ES higher than E+S)
• small peak
• no chemistry is happening
• requires the dissolvation of E and S (remove h2o so that S can bind E)

part2: ES –> EP
- exergonic reaction (ES higher than EP)
- largest peak of entire reation
- chemistry is happening
- have bond rearangements

part 3: EP –> E + P

• exergonic reaction (EP higher than E + P)
• small peak
• no chemistry is happening
• have dissociation and re-solvation of E and P

Question 3

ΔG for the uncatalyzed conversion of S–>P is ______ (greater or less) than the ΔG for catalyzed conversion of S–>P

Answer 3

much greater

Question 4

what do we call the difference in energy between the catalyzed and uncatalyzed transiton states for a rxn?

Answer 4

ΔGb = bidning energy

Question 5

what are the 3 effects of enzymes that allow them to lower the energy of the transition state?

Answer 5

(1) enzymes form interactions with the substrate and with the transition state
(2) some can change the reaction path
(3) all enzymes have proximity and orientation effects

Question 6

explain generally the interactions between enzymes/substrates/transiton states (what type of reactions are they and what purpose do they serve)

Answer 6

• hydrophobic, electrostatic, h-bonds

- act as the source of binding energy to lower the transition state energy

Question 7

are there enzymatic interactions dierctly involved in decreasing the energy of the transition state? if so provide an example, if not why?

Answer 7

• yes

- electrostatic interactions that compensate for the generation of charges in the transition state

Question 8

explain the enzymatic interactions that aid in binding substrate to the enzyme

Answer 8

• interactions help determine specificity

- interactions help align functional groups in the ezyme and substrate so the reaction can occur

Question 9

are enzymes perfectly complementary to the substrate?

Answer 9

no

Question 10

with what does the enzyme make optimal interactions?

Answer 10

the transition state

Question 11

what would happen if the substrate binded to the enzyme tighter than the transition state did?

Answer 11

the reaction would not be accelerated

Question 12

is the catalyzed transition state still a high energy state?

Answer 12

yes - still unstable and transient

Question 13

describe how some enzymes are able to change reaction paths

in terms of ΔG, what is the result?

Answer 13

• do so through the rearrangement of covalent bonds
• allows the formation of transient covalent bonds between the enzyme and substrate
• results in a lower overall ΔG of the catalyzed transition state

Question 14

describe the proximity and orientation effects of enzymes

Answer 14

substrate binds to an enzyme such that reactive groups are optimally positioned and oritented for the reaction to occur