Energy I

Question 1

What is Catabolism?

Answer 1

It is the breakdown of complex mechanisms to release energy or carry out mechanical work.

Question 2

What is Anabolism?

Answer 2

It is the synthesis of new molecules from less complex compounds.

Question 3

What is ATP in terms of energy/energy storage?

Answer 3

ATP is a body’s energy provision. It can act as both an acceptor and donator of energy. It acts as a short-term reservoir of energy.

Question 4

What regulates glycolysis?

Answer 4

Enzymes catalysing irreversible reactions are potential sites for regulation.
They are regulated by:
- reversible binding of allosteric effectors
- covalent modification
- transcription

Question 5

Describe the whole process in which glucose is converted to pyruvate.

Answer 5

1) Glucose is phosphorylated by Hexokinase to G6P (using ATP, making ADP).
2) G6P is them converted to Fructose-6-phosphate.
3) Fructose-6-phosphate is then phosphorylated by Phospho-fructokinase (PFK) to Fructose 1,6 bisphosphate (using ATP, making ADP).
4) Fructose 1,6 bisphosphate is then converted to two C3 molecules, Dihydroxy acetone phosphate and GALP (Glyceraldehyde-3-phosphate). These 2 molecules are kept in equilibrium, and it favours GALP.
5) GALP is then converted to phosphoenol pyruvate (using NAD+ and Pi, and ADP, making NADH and ATP).
6) Phosphoenol pyruvate is then converted by Pyruvate Kinase to pyruvate (using ADP, making ATP).

Question 6

List the three enzymes we need to know involved in glycolysis, and list what they are inhibited by.

Answer 6

Hexokinase:

• converts glucose to G6P
• inhibited by G6P

Phospho-fructokinase:
- converts fructose-6-phosphate
- inhibited by ATP, citrate and H+ (acids)
- stimulated by F26BP and AMP
(the inhibition of PFK leads to the inhibition of G6P)

Pyruvate Kinase:

• converts phosphoenol pyruvate to pyruvate
• inhibited by ATP

Question 7

What is relevant about the liver, in terms of glycolysis?

Answer 7

There are two enzymes that convert glucose to G6P: Hexokinase and Glucokinase. Hexokinase is found in (pretty much) all cells in the body, and Glucokinase is found mainly in hepatic cells. Glucokinase works at higher glucose levels, and isn’t inhibited by G6P.

Question 8

What difference in the cycle occurs when the respiration is anaerobic?

Answer 8

Instead of pyruvate being converted to Acetyl CoA, in anaerobically respiring muscle, it is converted to lactate (using NADH, making NAD+). The lactate is then sent to the liver to be converted back into glucose (so that the build-up of acid doesn’t inhibit PFK), and put back into the cycle.
The making of lactate uses NADH to make NAD+. This NAD+ is used in the conversion of GALP to phosphoenol pyruvate. This continues until NAD+ is a limiting factor.

Question 9

Describe anaerobic respiration’s role in a tumour’s growth.

Answer 9

When a tumour outgrows it’s blood supply, oxygen delivery is reduced, and tumour cell metabolism reverts to glycolysis.
A reduction in oxygen leads to the activation of the transcription factor HIF-1α. This regulates the expression of a number of enzymes in the glycotic pathway.