EN: Aerobic Respiration

Question 1

Link reaction.

Answer 1

Stage after glycolysis which converts pyruvate to acetyl coenzyme A.

Question 2

Stage after glycolysis which converts pyruvate to acetyl coenzyme A.

Answer 2

Link reaction.

Question 3

Where does the link reaction occur?

Answer 3

In the mitochondrial matrix.

Question 4

Pyruvate is decarboxylated - what does this mean?

Answer 4

One carbon atom is removed from pyruvate in the form of CO₂.

Question 5

Briefly describe the stages of the link reaction:

Answer 5

• Pyruvate is decarboxylated - carbon is removed in form of CO₂.
• Pyruvate is oxidised to form acetate and NAD is reduced to form reduced NAD.
• Acetate is combined with coenzyme A (CoA) to form acetyl coenzyme A.

No ATP is produced.

Question 6

Is ATP produced in the Link reaction?

Answer 6

No, none is produced.

Question 7

Draw a diagram to represent the link reaction:

Answer 7

Question 8

Briefly describe the stages of aerobic respiration:

Answer 8

• Glycolysis
• Link reaction
• Krebs cycle
• Oxidative phosphorylation

Question 9

How many pyruvate molecules are made for every glucose molecule that enters glycolysis?

What does this mean?

Answer 9

2

Means for each glucose molecule:

• 2 molecules of acetyl coenzyme A go into the Krebs cycle.
• 2 CO₂ molecules are released as waste products.
• 2 molecules of reduced NAD are formed and go to oxidative phosphorylation.

Question 10

Where does the Krebs cycle occur?

Answer 10

Mitochondrial matrix

Question 11

What does the Krebs cycle produce?

Answer 11

Reduced coenzymes and ATP

Question 12

Briefly, what does the Krebs cycle involve?

Answer 12

A series of oxidation-reduction reactions

Question 13

How many times does the Krebs cycle happen for pyruvate molecules?

How many times does it happen for glucose molecules?

Answer 13

Pyruvate = once

Glucose = twice

Question 14

What happens in the first part of the Krebs cycle?

Answer 14

• Acetyl CoA from link reaction combines with 4C molecule (oxaloacetate) to form a 6C molecule (citrate).
• Coenzyme A goes back to link reaction.

Question 15

What happens in the second part of the Krebs cycle?

Answer 15

• 6C citrate molecule is converted to 5C molecule.
• Decarboxylation occurs - CO₂ removed.
• Dehydrogenation occurs.
• Hydrogen is used to produce reduced NAD from NAD.

Question 16

What happens in the third stage of the Krebs cycle?

Answer 16

• 5C molecule is converted to 4C.
• Decarboxylation and dehydrogenation - produce 1 molecule of reduced FAD and 2 reduced NAD.
• ATP produced by direct transfer of a phosphate group from an intermediate compound to ADP - substrate-level phosphorylation.
• Citrate converts to oxaloacete.

Question 17

Substrate-level phosphorylation

Answer 17

A phosphate group is directly transferred from one molecule to another.

Question 18

A phosphate group is directly transferred from one molecule to another.

Answer 18

Substrate-level phosphorylation

Question 19

Draw a diagram to represent the Krebs cycle:

Answer 19

Question 20

What are all the products of one Krebs cycle?

Where does each go?

Answer 20

1 coenzyme A = reused in the next link reaction.

Oxaloacetate = regenerated for use in the next Krebs cycle.

2CO₂ = released as waste product.

1 ATP = used for energy.

3 reduced NAD = oxidative phosphorylation.

1 reduced FAD = oxidative phosphorylation.

Question 21

Relavatively speaking, how much ATP does oxidative phosphorylation produce?

Answer 21

Lots.

Question 22

Oxidative phosphorylation.

Answer 22

The process where the energy carried by electrons, from reduced coenzymes (FAD and NAD), is used to make ATP.

Question 23

The process where the energy carried by electrons, from reduced coenzymes (FAD and NAD), is used to make ATP.

Answer 23

Oxidative phosphorylation.

Question 24

What is the point of glycolysis, the Link reaction and the Krebs cycle?

Answer 24

To make reduced NAD and reduced FAD for the final stage - oxidative phosphorylation.

Question 25

Describe the process of oxidative phosphorylation.

Answer 25

• H atoms are released from reduced NAD and FAD when they are oxidised.
• H atom splits to H+ and e-
• e- move down electron transport chain, losing energy at each carrier.
• Energy is used to pump protons from mitochondrial matrix to intermembrane space.
• Concentration of H+ is higher in intermembrane space than in mitochondrial matrix - electrochemical graident forms.
• Protons move back to matrix through ATP synthase - drives the synthesis of ATP from ADP and Pi - chemiosmosis.
• At the end of ETC, protons, electrons and O₂ combine to form water - oxygen is the terminal electron acceptor.

Question 26

Why do protons diffuse through ATP synthase?

Answer 26

It is the only part of the inner mitochondiral membrane permeable to them.

Question 27

What happens to the regenrated coenzymes (FAD and NAD) made in oxidative phosphorylation?

Answer 27

They are reused in the Krebs cycle.

Question 28

In oxidative phosphorylation, where do protons move to and from?

Answer 28

From mitochondrial matrix to the intermembrane space and back again.

Question 29

How many ATP molecules are made from each molecule of reduced NAD?

How many ATP molecules are made from each molecule of reduced FAD?

Answer 29

Reduced NAD = 2.5 ATP

Reduced FAD = 1.5 ATP

Question 30

Draw a table to demonstrate the total amount of ATP produced in aerobic respiration:

Answer 30

Question 31

What can ATP production be affected by?

Answer 31

Mitochondrial diseases.

Question 32

How can mitochondrial diseases affect ATP production?

Answer 32

• Affect mitondria - can affect how proteins involved inn oxidative phosphorylation or Krebs cycle function, so reducing ATP production.
• May cause anaerobic respiration to increase to make up for ATP shortage.
• Lots of lactate is produced - can cause fatigue and weakness.
• Lactate can also diffuse into bloodstream, leading to high lactate concentrations.