Topic 8.1: Metabolism

Question 1

Definition of metabolism

Answer 1

Web of all the enzyme-catalysed reactions in a cell

Question 2

Metabolic pathways

Answer 2

Consist of chains and cycles of enzyme-catalysed reactions

Question 3

Example of chains of enzyme catalyzed reactions

Answer 3

Glycolysis

Question 4

Example of cycle of enzyme catalyzed reactions

Answer 4

Krebs cycle

Calvin cycle

Question 5

Definition of activation energy

Answer 5

Required amount of energy for a chemical reaction to proceed

Question 6

How do enzymes speed up the rate of a biochemical reaction?

Answer 6

a) Lowering the activation energy

b) Stressing and destabilising the bonds in the substrate

Question 7

Types of enzymatic reactions

Answer 7

a) Exergonic (Release of energy to the environment)

b) Endergonic (Absorbance of energy from the environment)

Question 8

Definition of enzyme inhibitor

Answer 8

Molecule that disrupts the normal reaction pathway between an enzyme and a substrate

Question 9

Normal enzyme reaction (3)

Answer 9

a) A substrate binds to an enzyme
b) The active site undergoes a conformational change to optimally interact with the substrate
c) Substrate is converted into product at an accelerated rate

Question 10

Competitive inhibition (2)

Answer 10

a) Molecule, other than substrate, blocking the active site, preventing substrate from binding to it.
b) Its effects can be reduced by increasing substrate concentration.

Question 11

Noncompetitive inhibition (2)

Answer 11

a) Molecule binding to an allosteric site, causing a conformational change in the active site and substrate cannot bind to it
b) Its effects cannot be mitigated by increasing substrate concentration.

Question 12

Example of competitive inhibition

Answer 12

a) Treatment of influenza (Relenza)

b) Relenza competitively binds to the neuraminidase active site and prevents the cleavage of the protein4

Question 13

Example of noncompetitive inhibition

Answer 13

a) Cyanide is a poison which prevents ATP production via aerobic respiration, leading to eventual death
b) By changing the shape of the active site, cytochrome oxidase can no longer pass electrons to the final acceptor (oxygen)

Question 14

Definition of end-product inhibition

Answer 14

Negative feedback by which metabolic pathways can be controlled

Question 15

Process of end-product inhibition

Answer 15

a) The final product in a series of reactions inhibits an enzyme from an earlier step in the sequence
b) The product binds to an allosteric site and temporarily inactivates the enzyme

Question 16

Purpose of end-product inhibition

Answer 16

Ensure levels of an essential product are always tightly regulated

Question 17

End-product inhibition of the pathway that converts threonine to isoleucine

Answer 17

a) Isoleucine may be synthesised from threonine in a five-step reaction pathway
b) First, threonine is converted into an intermediate compound by an enzyme.
c) Isoleucine can bind to an allosteric site on this enzyme and function as a non-competitive inhibitor

Question 18

Competitive inhibition and maximum rate of enzyme activity

Answer 18

It can still be achieved by increasing substrate concentration

Question 19

Noncompetitive inhibition and maximum rate of enzyme activity

Answer 19

The maximum rate of enzyme activity is reduced although substrate concentrations increase

Question 20

Lock and Key Model

Answer 20

a) Active site complements the substrate precisely

b) Explains specificity

Question 21

Induced Fit Model

Answer 21

a) Active site undergo conformational change when exposed to a substrate to improve binding.
b) Explains broad specificity and catalysis