Unit 2 - Metabolism and Survival (Cellular Respiration)

Question 1

What are the three pathways of aerobic respiration?

Answer 1

• Glycolysis
• The Citric Acid Cycle
• The Electron Transport Chain

Question 2

What is glycolysis?

Answer 2

Glycolysis is the breakdown of glucose to two pyruvate molecules. This process does not require oxygen (it is anaerobic).

Question 3

What is the role of ATP in glycolysis?

Answer 3

ATP is required for the phosphorylation of glucose and intermediates during the energy investment phase of glycolysis. (2 ATP). This leads to the generation of more ATP during the energy pay-off stage (4 ATP) and results in a net gain of ATP (net gain of 2 ATP).

Question 4

What is the role of dehydrogenase enzymes in glycolysis?

Answer 4

Dehydrogenase enzymes remove hydrogen ions and electrons and pass them to the coenzyme NAD, forming NADH. This occurs in both glycolysis and the citric acid cycle. The hydrogen ions and electrons are passed to the electron transport chain on the inner mitochondrial membrane. This occurs in both glycolysis and the citric acid cycle.

Question 5

What is the citric acid cycle?

Answer 5

In aerobic conditions, pyruvate is converted into an acetyl group that combines with coenzyme A forming acetyl coenzyme A. NADH and carbon dioxide are also formed during this process. In the citric cycle, the acetyl group from acetyl coenzyme A combines with oxaloacetate to form citrate. During a series of enzyme-controlled steps, citrate is gradually converted back into back into oxaloacetate which results in the generation on ATP and release of carbon dioxide.

Question 6

Where does glycolysis occur?

Answer 6

The cytoplasm

Question 7

Where does the citric acid cycle occur?

Answer 7

The matrix of the mitochondria

Question 8

Where does the electron transport chain occur?

Answer 8

In the proteins within the inner membrane (cristae)

Question 9

What is the electron transport chain?

Answer 9

• Electron transport chain
  The electron transport chain is the last stage of the respiration pathway and is the stage that produces the most ATP molecules.
• The electron transport chain is a series of carrier proteins attached to the inner mitochondrial membrane.
• Electrons are passed along the electron transport chain releasing energy.
• This energy allows hydrogen ions to be pumped across the inner mitochondrial membrane.
• The flow of these ions back through the membrane protein ATP synthase results in the production of ATP.
• Oxygen is the final hydrogen ion and electron acceptor.
• Finally, the hydrogen ions and electrons combine with oxygen to form water.

Question 10

What is fermentation?

Answer 10

In the absence of oxygen, fermentation takes place in the cytoplasm. Fermentation results in much less ATP being produced than in aerobic respiration.

Question 11

What happens during fermentation in an animal cell?

Answer 11

In animal cells, pyruvate is converted to lactate in a reversible reaction.

Question 12

What happens during fermentation in plant and yeast cells?

Answer 12

In plants and yeast, ethanol and carbon dioxide are produced in an irreversible reaction.

Question 13

What is the role of ATP?

Answer 13

ATP is used to transfer energy to cellular processes which require energy, such as:
- Nerve transmission
- Muscle contraction
- Active transport