Respiration

Question 1

What is the first stage of both aerobic/anaerobic respiration?

Answer 1

Glycolysis

Question 2

What happens in glycolysis and what is produced at the end?

Where does it occur?

What is the overall yield?

Answer 2

• Upon glucose’s entry to the cytoplasm, an enzyme phosphorylated glucose with two ATP molecules to form hexose bisphosphate and two ADP molecules. The hexose bisphosphate then breaks down into two triose phosphate molecules. Another phosphate is added. Triose phosphate is oxidised (loses hydrogen) and NAD is converted to NADH. Then the molecules form two pyruvate molecules and 4 ATP (2 each.)
• Cytoplasm
• 2 ATP Molecules

Question 3

Why do we make hexose bisphosphate instead of breaking down the glucose immediately?

Answer 3

Glucose enters the cells via facilitated diffusion, if there is more glucose inside the cell than outside, it will diffuse out. By phosphorylating it to form hexose bisphosphate, the glucose is essentially trapped inside the cell as it can’t diffuse via the transport proteins.

Question 4

What is dehydrogenation an example of?

Answer 4

Oxidation (loss of Hydrogen)

• Extra: Reduction (gain of Hydrogen)

Question 5

What is an oxidation-reduction reaction?

Answer 5

Oxidation and reduction always occur together

Question 6

How are the two pyruvate molecules transported to the mitochondrial matrix from the cytoplasm?

Answer 6

Active transport/co-transport with the energy not coming from ATP

Question 7

Explain the Link Reaction.

Answer 7

Once the pyruvate molecule enters the mitochondrial matrix, it loses carbon dioxide (decarboxylation) and hydrogen (oxidised which reduces NAD) to form acetate which then combines with Coenzyme A to form Acetyl Coenzyme A.

Question 8

What are the two coenzymes involved in the Link Reaction?

Answer 8

• Coenzyme A
• NAD

Question 9

What is the 4/6 carbon molecules called in the Krebs cycle?

Answer 9

• Oxaloacetate (which combines with acetyl CoA)
• Citrate

Question 10

Brief outline of Krebs cycle.

Answer 10

Oxaloacetate reacts with Acetyl CoA to form citrate (the CoA is removed) which then loses two carbons in the form of CO2 (decarboxylation). An ATP molecule is produced.

Question 11

Why do we use CoA when it is removed?

Answer 11

The reaction of oxaloacetate and Acetyl CoA is catalysed by an enzyme.

Question 12

How is ATP made in glycolysis and the Krebs cycle?

Answer 12

Substrate-level phosphorylation

Question 13

What are the four molecules produced in the Krebs cycle?

Which are the three important ones?

Answer 13

• Two CO2
• 3 NAD to 3 NADH (reduced) from dehydrogenation of citrate
• FAD to FADH2
• ADP to ATP

Question 14

How many ATP molecules are produced in:

• Glycolysis
• Link Reaction
• Krebs Cycle

Answer 14

• 2
• 0
• 2

Question 15

What happens in the fourth stage of aerobic respiration?

Answer 15

ADP is converted to ATP with the use of energy in ATP synthase. This energy is supplied by the movement of H+ ions down a proton gradient from the intermembrane space to the matrix. To maintain this electrochemical gradient, proton pumps actively transport H+ ions from the matrix to the intermembrane space.

Question 16

Explain the ETC

Answer 16

A NAD/FADH2 donates two electrons to a protein in the inner mitochondrial membrane, then by a series of oxidation-reduction reactions electrons are transported from protein to protein (ETC) and energy is released. This energy allows for H+ ions to be actively transported from the matrix into the intermembrane space. At the end of the chain, electrons react with O2 and H+ to form H2O. Aerobic respiration only happens when there is enough O2 to be the final electron acceptor.

Question 17

What does NADH donate in the ETC?

What does FADH2 donate in the ETC?

Answer 17

• 2 electrons, H+, NAD
• 2 electrons (to the second protein in the ETC in the inner mitochondrial membrane), 2H+, FAD