2.2) Cellular Respiration

Question 1

• What are the 3 stages of cellular respiration?

Answer 1

1. Glycolysis
2. Citric Acid Cycle
3. Electron Transport Chain

Question 2

• What is ATP and what is its role?

Answer 2

• ATP (Adenosine Triphosphate)
  ➞ is a high-energy molecule used to transfer energy to cellular processes which require energy.
• EXAMPLES:
  ➞ muscle cell contraction
  ➞ cell division
  ➞ protein synthesis
  ➞ DNA replication

Question 3

• What is ‘phosphorylation’?

Answer 3

• ‘Phosphorylation’
  ➞ an eznyme-controlled process by which a phosphate group is added to a molecule.
• It can also occur when a phosphate and energy are transferred from ATP to the molecules of a reactant in a metabolic pathway,
  ➞ making them more reactive.
  ↳ Often a step can only proceed if the reactant becomes phosphorylated and energised.

Question 4

• What is the summary of ‘glycolysis’?

Answer 4

1. Glycolysis is the breakdown of glucose to pyruvate.
2. It occurs in the cytoplasm.
3. It consists of 2 stages:
   ➞ energy investment phase and energy pay-off phase.
4. During the energy investment phase, 2 ATP are used up to phosphorylate glucose and intermediates.
5. This leads to the generation of 4 ATP during the energy pay-off stage.
6. There is an overall net gain of 2 ATP during glycolysis.
7. Dehydrogenase enzymes remove hydrogen ions and electrons from intermediates
   ➞ which are collected by NAD/hydrogen carrier molecule.

Question 5

• What are ‘aerobic conditions’?

Answer 5

• In aerobic conditions,
  ➞ pyruvate is broken down to an acetyl group that combines with coenzyme A to form acetyl coenzyme A.
• Acetyl CoA will then proceed from the cytoplasm to the matrix of the mitochondria for Stage 2 of respiration
  ➞ the citric acid cycle.

Question 6

• What is the summary of the ‘citric acid cycle’?

Answer 6

1. It occurs in the matrix of the mitochondria.
2. Pyruvate is converted to an acetyl group.
3. The acetyl group combines with coenzyme A to form acetyl coenzyme A.
4. Acetyl coenzyme A combines with oxaloacetate to form citrate.
5. Citrate is converted back into oxaloacetate in a series of enzyme-controlled steps.
6. Carbon dioxide is released and (some) ATP is produced.
7. Dehydrogenase enzymes remove hydrogen ions/high energy electrons from intermediates,
   ➞ collected by NAD+

Question 7

• Describe the further role of ‘dehydrogenase enzymes’

Answer 7

• The H+ ions are passed onto coenzymes NAD to form NADH
  ➞ which occurs in both glycolysis and the citric acid cycle.
  ↳ The H+ ions and electrons from NADH are then passed to the electron transport chain on the inner mitchondrial membrane.

Question 8

• What is the summary of the ‘electron transport chain’?

Answer 8

1. It occurs in the inner mitchondrial membrane.
2. Hydrogen ions/electrons are passed to (coenzymes) NAD/FAD.
3. NADH/FADH release electrons to the electron transport chain.
4. Electrons are passed along the chain of carrier proteins.
5. Energy is released which pumps hydrogen ions across the inner mitochondrial membrane.
6. The return flow of hydrogen ions/electrons synthesises ATP,
   ➞ through the enzyme ATP synthase.
7. Oxygen acts as the final hydrogen/electron acceptor,
   ➞ and combines with hydrogen to form water.