Carbohydrates

Question 1

What is the simplest form of carbohydrates and name some examples.

Answer 1

Monosaccharides - glucose, fructose, galactose.

Question 2

What are disaccharides and give some examples.

Answer 2

Composed of two monosaccharide units linked together - sucrose, lactose, maltose.

Question 3

What is a polysaccharide and give some examples.

Answer 3

Long chains of monosaccharide units - starch, glycogen, cellulose.

Question 4

What is the role of glycogen in the liver?

Answer 4

Maintains blood glucose levels, especially during fasting.

Question 5

Describe glycogenolysis in the liver and compare this to muscle.

Answer 5

The liver releases glucose into the bloodstream by breaking down glycogen, mediated by the enzyme glycogen phosphorylase. The glucose-6-phosphate generated is converted to free glucose by glucose-6-phosphatase, which is absent in muscle.

Question 6

What is the role of glycogen in the muscle?

Answer 6

Provides energy for muscle contraction during physical activity.

Question 7

Describe glycogen breakdown in the muscle.

Answer 7

Muscle glycogen is broken down to glucose-6-phosphate, but since muscle cells lack glucose-6-phosphatase, glucose cannot be released into the bloodstream. Instead, it enters glycolysis to generate ATP.

Question 8

Describe Type 1 GSD (Von Gierke’s Disease).

Answer 8

Deficiency of glucose-6-phosphatase in the liver, leading to the inability to release glucose into the bloodstream, causing hypoglycemia, lactic acidosis, and hepatomegaly.

Question 9

List the key steps in glycolysis.

Answer 9

1. Glucose enters the cytoplasm.
2. 2. Glucose is phosphorylated to hexose-1,6-biphosphate. This requires the hydrolysis of 2 ATP molecules.
3. Hexose-1,6-biphosphate is split into two triose phosphates (TP).
4. Triose phosphate is oxidised. Each TP molecule loses two hydrogen atoms (oxidation). NAD combines with the released hydrogens, making reduced NAD. 2 ATP molecules are made.
5. Triose phosphate is converted to pyruvate. This conversion produces another 2 ATP.

Question 10

What is the purpose of glycolysis?

Answer 10

Breaks down glucose to produce ATP, pyruvate, and NADH.

Question 11

What is the purpose of gluconeogenesis and where does it occur?

Answer 11

Synthesizes glucose from non-carbohydrate precursors such as lactate, glycerol, and amino acids (primarily in the liver and kidney).

Question 12

What situations require gluconeogenesis?

Answer 12

• Fasting/starvation (glycogen stores depleted).
• Intense exercise (lactate is used to regenerate glucose).
• Ruminant carbohydrate metabolism.

Question 13

Describe the importance of the Kreb’s cycle in carbohydrate metabolism.

Answer 13

1. Acetyl-CoA enters; oxidised to produce NADH, FADH₂ and ATP.
2. The NADH and FADH₂ generated are used in the electron transport chain (ETC) to produce ATP via oxidative phosphorylation.

Question 14

What is the process of aerobic glycolysis?

Answer 14

Glucose is broken down to pyruvate, which is further oxidized in the mitochondria via the TCA cycle and the electron transport chain (ETC) to produce ATP.

Question 15

List the advantages of aerobic glycolysis.

Answer 15

1. Produces significantly more ATP (~30-32 ATP per glucose) compared to anaerobic glycolysis.
2. Efficient energy generation, suitable for sustained activities.

Question 16

List the disadvantages of aerobic glycolysis.

Answer 16

1. Slower process compared to anaerobic glycolysis.
2. Dependent on oxygen availability; cannot function under anaerobic conditions.

Question 17

Describe the process of anaerobic glycolysis.

Answer 17

In the absence of oxygen, pyruvate is converted into lactate by lactate dehydrogenase to regenerate NAD⁺ for continued glycolysis.

Question 18

List the advantages of anaerobic glycolysis.

Answer 18

1. Rapid ATP production (2 ATP per glucose), which is beneficial during high-intensity, short-term activities (e.g., sprinting).
2. Functions in low-oxygen environments (e.g., during intense exercise or in tissues with limited oxygen supply).

Question 19

List the disadvantages of anaerobic glycolysis.

Answer 19

1. Produces much less ATP (only 2 ATP per glucose).
2. Lactate accumulation leads to muscle fatigue and acidosis.