Chaptr 3 - Enzymes And Biochemical Pathways

Question 1

What are enzymes?

Answer 1

Biological catalysts (speed up the rate of reaction), proteins, not used up in the reaction, recycled over and over again.

Question 2

Define

1. Monomeric enzymes

2. Oligomers

Answer 2

1. Enzymes that consist of a single polypeptide chain.

2. Enzymes consisting of two or more polypeptide chains.

Question 3

Why are enzymes so specific?

Answer 3

Due to the active site on the enzyme being complimentary in shape to the structure of the substrate.

Question 4

1. Lock and key model
2. Induced fit mode

• diagrams pg9

Answer 4

1. The substrate and enzyme active site have complimentary shapes; active site is rigid and fixed.
2. The active site changes its shape to fit tightly around its substrate; active site is not fixed, forms complimentary shape —> reaction complete —> returns to relaxing state.

Question 5

Two type of chemical reactions

1. Anabolic reactions
2. Catabolic reactions

Answer 5

1. Building of larger molecules (polymers) from smaller molecules (monomers), chemical bonds created, needs ATP, endergonic (requires absorption of energy) = dehydration/condensation = water lost.
2. Breaking down of macromolecules (polymers) into smaller molecules, chemical bonds broken, energy released = exergonic = hydrolysis = adding water.

Question 6

Activation energy

1. Define
2. Enzymes relation?

*graph diagram pg10

Answer 6

1. The minimum amount of energy that is required to activate atoms or molecules to a condition in which they can undergo chemical transformation or physical transport.
2. Enzymes lower the activation energy required.

Question 7

Are of enzyme-catalysed reactions depend on?

Answer 7

Concave downwards
• substrate concentration
• enzyme concentration

Bell curves:
• pH concentration
• temperature concentration

Question 8

Enzyme inhibition

1. Define enzyme inhibitor
2. Two types of inhibition

Answer 8

1. A molecule that binds to an enzyme and interferes with its ability to function.
2. • Irreversible inhibition = permanent inactivation of an enzyme; a compound forms strong covalent linkages with amino acids at the active site of an enzyme, alters the structure I the enzyme and active site, poisons such as cyanide act this way.
   • reversible inhibition = temporary inactivation if an enzyme; a compound forms weak non-covalent linkages with amino acids at the active site of the enzyme, inhibitor can be removed, enzyme can function again.

Question 9

Two types of reversible inhibition?

*diagrams pg11

Answer 9

1. Competitive inhibition
   • inhibitor has a similar shape to the usual substrate, binds to the active site of the enzyme, preventing the formation of the enzyme-substrate complete, reducing the rate of reaction.
2. Non-competitive = inhibitor does not bind to the active site, inhibitor binds to another site called the allosteric site. This distorts the 3D shape of the enzyme, including the active site, so it can no longer bind to its substrate, so the enzyme is inactivated.

Question 10

Define

1. Cofactors
2. Coenzymes

• organic cofactors = coenzymes or prosthetic groups.

Answer 10

1. Additional non-protein components that endure the stability and functionality for some enzymes.
2. Addition non-protein organic components that can move energy, protons and electrons between reactions in the cell.

Question 11

ATP (adenosine triphosphate)

1. Is?
2. Process?

• ADP is regenerated to ATP during cellular respiration
• diagram pg12

Answer 11

1. A co-enzyme that transfers energy around the cell.
2. ATP and the reactants dock with the enzyme. A phosphate group is transferred to the reactant from ATP, creating ADP and a phosphorylated reactant. Energy is release and a hydroxide from a H2O takes the place of the third phosphate group. The phosphorylated reactant now has the energy to react with another reaction. Then hydroxide from H2O is release, phosphate is added. forming ATP.

Question 12

NADH & NADPH

1. Role?
2. Loaded form of NAD + examples
3. Unloaded form of NAD + examples

Answer 12

1. NADH & NADPH act as coenzymes, but they help transfer proteins and electrons between substrates and reactions.
2. A source of electrons and a helper for any enzyme that catalyses a reaction in which its substrate is reduced. E.g. ATP/NADH/NADPH.
3. Where NAD is a receiver of electrons and is a helper for any enzyme that catalyses a reaction in which its substrate is oxidised. E.g. ADP/NAD+/NADP+.