Question

1. Why do fats provide more energy per molecule than glucose? Explain your answer in terms

of the electrons extracted during the process of cellular respiration.

2. A rare, frameshift genetic mutation can alter the structure of the Pyruvate Dehydrogenase

Complex such that it no longer functions within the cell. Describe what parts of the process

of cellular respiration would be impacted due to this non-functional enzyme.

3. The citric acid cycle functions to completely oxidize glucose in the presence of oxygen,

allowing for a large amount of ATP to be produced within the cell through oxidative

phosphorylation. Free oxygen did not always exist within the atmosphere of Earth, meaning

that early life forms relied solely on glycolysis and fermentation to extract energy from

macromolecules. What role did the increase in atmospheric oxygen play in the evolution of

life on Earth? Frame your answer in terms of the energy derived from cellular respiration in

the presence and absence of oxygen.

Answer 1

1. Fats are more energy-rich compounds as compared to carbohydrates.
i.e. they store more energy per gram.
1 g of Carbohydrate = 4 calories
1 g of Fat = 9 calories
This is due to the fact that Carbon:Oxygen ratio in carbohydrates is equal to one. So, they contain less amount reducing equivalents.
In contrast, the Carbon:Oxygen ratio in fats is very high i.e. they contain more carbon atoms than oxygen atoms. i.e. they contain more amount reducing equivalents.

1 mole of glucose produces 32-38 ATP.
1 mole of Palmitic acid produces 131 ATP.

Fatty acids undergo beta-oxidation to produce Acetyl CoA.
Acetyl CoA enters the TCA cycle to produce NADH, FADH2, and ATP.

2. Pyruvate dehydrogenase is an essential enzyme in the aerobic respiration. It catalyzes the link reaction that connects glycolysis to the TCA cycle.
It catalyzes the oxidative carboxylation of pyruvate to acetyl CoA.

Pyruvate + NAD+ + CoASH -------> Acetyl CoA + NADH + CO2

If Pyruvate dehydrogenase is mutated, carbohydrates cannot enter the TCA cycle.

3. The presence of oxygen favoured the evolution of aerobic organisms. This is due to the fact that aerobic respiration produces more energy as compared to anaerobic respiration.
Aerobic respiration of one glucose moelcule produces 32-38 ATP.
Anaerobic respiration of one glucose moelcule produces 2 ATP.