Control of metabolic pathways

Question 1

At irreversible steps

Answer 1

Increases in the rate of enzyme activity greatly increases the rate of the downstream steps

Question 2

Control levels

Answer 2

• Product inhibition

- Influence of signalling molecules such as hormones

Question 3

Typical blood glucose

Answer 3

Around 4mM

Question 4

Hexokinase - muscle + liver

Answer 4

Different forms (isoforms) of enzyme
Maximally active at different concentrations of glucose

Question 5

Michaelis constant (KM)

Answer 5

The concentration of substrate at which an enzyme functions at a half-maximal rate (Vmax)

Question 6

KM of Hexokinase I found in muscle

Answer 6

0.1mM: active at low concentrations of glucose and is essentially operating at maximal velocity at all times

Question 7

Hexokinase I inhibition

Answer 7

Highly sensitive to inhibition by the product glucose-6-phosptate
Under anaerobic conditions when the rate of the TCA cycle drops, and glycolysis slows, Hexokinase I is inhibited by accumulating levels of G-6-P

Question 8

Hexokinase IV in liver

Answer 8

KM of around 4mM: much less sensitive to blood glucose concentrations (right hand graph)
Also less sensitive to the inhibitory effects of G-6-P

Question 9

Glucose 6-phophatase (liver only)

Answer 9

Catalyses the reverse reaction to hexokinase, generating glucose from glucose-6-phosphate