Enzymes & Chemical Catalysis

Question 1

What is rate called?

Answer 1

Velocity (V)

Question 2

What are reactants called?

Answer 2

Substrates (S)

Question 3

Why should we care about enzymes?

Answer 3

1) lots of organic mechanism
2) lots of commercially available products
3) targets for drugs

Question 4

What does aspirin inhibit?

Answer 4

Inhibitor of cycloygenase

Question 5

What does Retrovir inhibit?

Answer 5

Inhibitor of reverse transcriptase (HIV)

Question 6

What does roundup inhibit?

Answer 6

Inhibits an enzyme involved in biosynthesis of aromatic amino acids

Question 7

What does tamiflu inhibits

Answer 7

Inhibitor of neuraminidade (flu)

Question 8

What does penicillin inhibit?

Answer 8

Inihibits a transpeptidase in peptidoglycan synthesis ( bacteria cell wall synthesis)

Question 9

Why are enzymes catalysts and why are they good catalysts?

Answer 9

They reduce the change in free energy- lower activation energy

1) reduce activation energy in mild conditions
2) immense catalytic power
3) exquist specificity

Question 10

What catalysts are used in Haver process?

Answer 10

Chemical- Fe- needs stronger conditions

Biological- nitrogenase- milder conditions (pH, temperature, pressure)

Question 11

What is the roll of glycosidase?

Answer 11

Cleaves sugars - add water, an alcohol leaves

Breaks the glycosidic bond (-O-R)

Question 12

Why are enzymes specific ?

Answer 12

They only interact with proteins of a complementary shape/ e.g. If there is small change to glucose - enzyme no longer works as they are specific
Indentations, grooves and pockets on the surface of the enzyme provide the complementary bonding side for substrates-
Induced fit- strain towards TS
Lock and key hypothesis

Question 13

What is the function of protease?

Answer 13

Hydrolysis of peptide bond (amide bond)
Protease and water react
( see mechanism)

Enzymes are active with certain R groups

Question 14

Name catalytic strategies

Answer 14

1) proximity and orientation
2) covalent catalysis (Nu attack)
3) general acid/ base catalysis
4) electrostatics
5) strain

Question 15

How does proximity and orientation increase rate?

Answer 15

Holding groups closer together- decreasing entropy
Holding the nucleophile closer to the electrophile and fix orientation increases the rate
- enzymes hold sugar in specific orientation and reduce rotation of side chain- hold close to active site

Question 16

What are enzyme non covalent interactions?

Answer 16

Enzymes harness the full range of non covalent interactions

• electrostatics
• ion dipole
• dipole- dipole
• H bonding
• hydrophobic

Question 17

What is covalent catalysis (Nu)

Answer 17

Enzyme intermediate in protein bonds to substrate and this drives the reaction forward as this increases the energy of the complex
ES is higher in energy then EP
- reaction via a short lived covalent intermediate

Question 18

How do you form an imine?

Answer 18

Add a primary amine to a C=O bond
Water is the leaving group
See mechanism

Question 19

How does retinal allow us to see?

Answer 19

Lysine acts a nucleophile and donates electrons from the nitrogen to the C=O bond on retinal
This causes imine formation
The imine can accept hv due to double bonds
This triggers a change in structure and allows us to see

Question 20

How do you form a ketone and CO2?

Answer 20

Catalysed by acetoacetate decarboxylase
Lycine attacked
Water also attacks and Co2 is released
(See mechanism)

Question 21

What is one or the best features of an enzymes ?

Answer 21

It can perform general acid and general base catalysis and at the same time

Question 22

Describe glycoside hydrolysis

Answer 22

The amino residue in the enzyme is deprotonated

The acid is held in close proximity and the glycosidic bond is protonated

Question 23

What pka do the enzyme residues need to have?

Answer 23

They need to have pka close to the pH you are working at so it can donate or accept a H

Question 24

What is electrostatic catalysis?

Answer 24

The enzyme has the ability to change its pH environment to bind to the transition state rather than the substrate
This drives the reaction forwards
There is an attraction between the positive surface and the negative ester intermediate (charge-charge interactions)

Question 25

What is the mechanism for Keto- enol tautomerisation?

Answer 25

See mechanism

Question 26

How does strain and distortion catalyse the reaction?

Answer 26

Epoxides are more reactive than the other ethers, it wants to relieve its strain and drive reaction forwards
The strain makes the process go faster
Enzymes harness the binding energy of the substrate to distort them to make them more reactive (higher energy)

Question 27

What do enzymes favour binding?

Answer 27

Enzymes favour binding to the transition state over the substrate

Question 28

What is the evidence that enzymes stabilise the transition state?

Answer 28

1) enzymes are inhibited by transition state mimics

2) antibodies raise against transition state mimics have catalytic activity

Question 29

What is the role of NAD+ coenzyme

Answer 29

From niacin

Oxidation or hydrogen transfer

Question 30

What is the role of FAD coenzyme

Answer 30

From riboflavin

Oxidation or hydrogen transfer

Question 31

What is the role of CoA coenzyme

Answer 31

From pantothenic acid

Acetyl group carrier

Question 32

What is the role of coenzyme B-12

Answer 32

From vitamin B-12

Methyl group transfer

Question 33

What is the role of TPP coenzyme

Answer 33

From thiamin (B-1)

Aldehyde group transfer

Question 34

Describe hydride addition

Answer 34

See mechanism