Week 5 - Carbohydrate metabolism

Question 1

What happens when a substrate is oxidised?

Answer 1

It gives up 2 hydrogen atoms - 1 is passed as a hydride ion (h-) to NAD+ (to make NADH) or FADH (to make FADH2) and the other is released as a proton (H+) to the aqueous environment (lowers pH).

Question 2

Is glycolysis aerobic or anaerobic?

Answer 2

Anaerobic

Question 3

Where does glycolysis take place?

Answer 3

Cytosol

Question 4

What is the reactant, and products of glycolysis?

Answer 4

Reactant - Glucose
Products - Pyruvate (3C)x2 and NADH

Question 5

What are the 2 key phases to glycolysis?

Answer 5

Investment phase
Pay-off phase

Question 6

What are the 4 ways in which exercise can speed up glycolysis?

Answer 6

• Substrate availability – increased glycogenolysis favours glycolysis to proceed.
• Physiological factors – greater flow of blood with exercise increases flow of glucose molecules towards active muscle.
• Cellular factors – increased glucose uptake by glucose transporters, such as GLUT4.
• Molecular factors – allosteric activation of pyruvate kinase and phosphofructokinase involved with glycolysis.

Question 7

Is the Krebs/Citric acid cycle aerobic or anaerobic?

Answer 7

Aerobic

Question 8

Where does the krebs cycle occur?

Answer 8

Mitochondrial matrix

Question 9

What are the reactants and products of the krebs cycle?

Answer 9

Reactant - Acetyl coA
Products - ATP, NADH, FADH2

Question 10

What enzyme oxidises pyruvate to acetyl coA?

Answer 10

pyruvate dehydrogenase. This in turn generates NADH

Question 11

As NADH is impermeable to mitochondrial membrane, how does it transfer its electrons into the mitochondria?

Answer 11

It transfers its electrons through a membranal enzyme to FADH.

Question 12

What happens to Gibbs free energy as electrons are transferred to NADH and FADH?

Answer 12

Gibbs free energy falls

Question 13

Is oxidative phosphorylation an aerobic or anaerobic pathway?

Answer 13

Aerobic

Question 14

Where does oxidative phosphorylation occur?

Answer 14

Mitochondrial intermembrane space and matrix

Question 15

What are the reactants and products of oxidative phosphorylation?

Answer 15

Reactants - 8 NADH & 4 FADH2
Products - 26 ATP, 6CO2, 6 H20

Question 16

What does the ETC do to NADH and FADH2?

Answer 16

Re-oxidises them back to their oxidised form, releasing H-

Question 17

During oxidative phosphorylation, in what direction are H+ ejected?

Answer 17

From the matrix to the intermembrane space, creating a concentration gradient

Question 18

What is the limiting factor of anaerobic metabolism?

Answer 18

Regeneration of ATP, NOT OXYGEN.

Question 19

During anaerobic respiration, what enzyme converts pyruvate to lactate?

Answer 19

Pyruvate dehydrogenase

Question 20

What is gluconeogenesis?

Answer 20

Where carbon skeletons from other molecules are used to synthesis glucose for energy provision in muscle

Question 21

Describe the cori cycle

Answer 21

When lactate leaves the working muscle, it enters the liver via the blood and reforms pyruvate, which can then be used as a substrate for gluconeogenesis. Glucose is then shuttled back to the active muscle.