Week 2 RAS live Lecture 3

Question 1

1) How are metabolic pathways regulated?

Answer 1

1) In 3 ways:
a) Coarse control – regulates enzyme levels (synthesis and breakdown)
b) Fine control – regulates the enzyme itself - allosteric control, covalent control (reversible)
c) Access – compartmentalisation (physical compartment or e.g. NADPH vs NADH)

Question 2

2) How do you control the first enzyme in a branched pathway?

Answer 2

2) 3 strategies:
a) Enzyme multiplicity (isozymes)
b) Single enzyme – cumulative control
c) Single enzyme – concerted control

Question 3

3) What is an example of a branched pathway?

Answer 3

3) Amino acid biosynthesis which forms lysine, methionine and threonine from Aspartic acid.

Question 4

4) What are isoenzymes?

Answer 4

4) Two or more enzymes with identical function but different structures. Differ in sequence but can catalyse same reactions.

Question 5

5) Example of an isoenzyme?

Answer 5

5) Aspartokinase. In E. coli there are 3 different types:
a) One that doesn’t inhibit anything
b) One that is inhibited by threonine
c) One that is inhibited by lysine
i) So, in the amino acid biosynthesis example, threonine and lysine inhibit the breakdown of aspartic acid.

Question 6

6) What is concerted allosteric control?

Answer 6

6) When 1 product does not have an effect on the enzyme, but when multiple types of product regulate the enzyme’s activity

Question 7

7) What is cumulative control?

Answer 7

7) When the products affect the enzyme activity.