Lecture 7: Enzymes - for life

Question 1

What is the general role of enzymes?

Answer 1

Enzymes increase reaction rates by lowering the energy (Ea) required to reach the transition state, allowing critical life processes to occur. They are not consumed in this process.

Question 2

Why do we need enzymes to catalyse biological reaction?

Answer 2

We need enzymes to catalyze biological reactions because they significantly increase the reaction rates, allowing essential processes in the body, like metabolism and digestion, to occur quickly and efficiently under normal physiological conditions. Without enzymes, these reactions would be too slow to sustain life.

Question 3

Will a biological process occur spontaneously if ΔG > 0? Why/Why not?

Answer 3

It will not occur spontaneously as ΔG > 0, so energy is required to drive the reaction forward.

Question 4

Do enzymes alter the equilibrium of a reaction?

Answer 4

No, they decrease activation energy, this accelerates the forward and backwards reaction equally thus the overall equilibrium for the reaction is not changed.

Question 5

How do enzymes effect the thermodynamics of a reaction?

Answer 5

Enzymes catalyse thermodynamically favourable reactions by lowering the activation energy. (No change to thermodynamics)

Question 6

What are the major classes of enzymes?

Answer 6

6 Classes: OTHLIL

Over The Hill Little Indians Leap

1. Oxidoreductases - RedOx (transfer of electrons)
2. Transferases - Transfer of a functional group
3. Hydrolases - Hydrolysis reactions (using H2O)
4. Lyases - Non-Hydrolytic breaking or making of bonds (no H2O)
5. Isomerases - Transfer of atoms/groups within a molecule to yield an isomeric form
6. Ligases - Join two molecules together (ie. form a new bond; usually coupled to ATP cleavage)

Question 7

What is a cofactor, and what purpose do they serve?

Answer 7

Many enzymes require other non-protein “factors” to help them catalyse reactions

Question 8

What are the two major classes of cofactor?

Answer 8

Metal ions and Coenzymes

Question 9

How do metal ions aid enzymes in metal ion catalytic mechanisms?

Answer 9

Are Lewis acids (electron acceptors), so they can particpate in acid-base catalysis.

Form co-ordination compounds with precise geometries (good for positioning reactants exactly where they need to be)

Question 10

List examples of enzymes that utilise Mg2+

Answer 10

DNA polymerase, hexokinase, pyruvate kinase

Question 10

List examples of enzymes that utilise Zn2+

Answer 10

Alcohol dehydrogenase, carbonic anhydrase

Question 11

List examples of enzymes that utilise Fe2+ or Fe3+

Answer 11

Cytochrome oxidase, peroxidase

Question 12

What is a coenzyme and how is it derived?

Answer 12

Coenzymes are small organic molecules, co-substrates and are carriers of (electrons, atoms or functional groups)

They are often derived from vitamins

Question 13

How do coenzymes aid in enzymatic reactions?

Answer 13

Coenzymes aid in enzymatic reactions by serving as carriers for chemical groups or electrons that are transferred during the reaction. They assist enzymes by temporarily holding or transferring molecules, thereby helping facilitate the chemical transformation and enhancing the enzyme’s activity.

Question 14

What is reaction coupling and how do enzymes mediate this?

Answer 14

Enzymes can couple a spontaneous reaction to a non-spontaneous one, to make the overall ΔG < 0.

For Example:
Hexokinase couples ATP reaction (-30.5kJ/mol) to glucose reaction (+13.8kJ/mol) resulting in an overall spontaneous reaction (-16.7kJ/mol)

ATP + Glucose —> Glucose-6-P + ADP

Enzymes mediate reaction coupling by bringing the two reactions together within their active sites, allowing the energy released from the spontaneous reaction to drive the non-spontaneous reaction.

Question 15

How does ‘PLP’ co-factor facilitate glycogen
phosphorylase activity?

Answer 15

PLP is covalently attached to a lysine at the active site, is good at donating a proton to Pi.

This processes helps stabilise the transition state and also helps to stabilize the negatively charged intermediates that form during glycogen breakdown, facilitating the release of glucose-1-phosphate.

Question 16

What is the metabolic network?

Answer 16

Biochemical synthesis and degradation uses pathways of enzyme catalyzed steps. The metabolic network keeps most of these individual steps away from equilibrium.