[12] Respiration

Question 1

What are the 4 stages of Aerobic respiration?

Answer 1

1. Glycolysis
2. Link Reaction
3. Krebs Cycle
4. Oxidative Phosphorylation

Question 2

Describe Glycolysis.

Answer 2

The splitting of the 6-carbon glucose molecule into two 3-carbon pyruvate molecules.

Question 3

Desribe the Link Reaction.

Answer 3

The 3-carbon pyruvate molecules enter into a series of reactions which lead to the formation of acetylcoenzyme A, a 2-carbon molecule.

Question 4

Describe the Krebs Cycle

Answer 4

The introduction of acetylcoenzyme A into a cycle of oxidation - reduction reactions that yield some ATP and a large quantity of reduced NAD and FAD.

Question 5

Describe Oxidative Phosphorylation.

Answer 5

The use of electrons, associated with reduced NAD and FAD, released from the Krebs Cycle to synthesise ATP with water produced as a by-product.

Question 6

What are the 4 stages of Glycolysis?

Answer 6

1. Phosphorylation of glucose to glucose phosphate (6C)
2. Splitting of the phosphorylated glucose into 2 triose phosphate molecules (3C)
3. Oxidation of triose phosphate (3C)
4. Production of 2 ATP from ADP

Question 7

What is the yield from one glucose molecule after glycolysis?

Answer 7

• Two molecules of ATP
• Two molecules of NADH
• Two molecules of pyruvate

Question 8

Where does glycolysis take place?

Answer 8

Cytoplasm

Question 9

What is the overall equation for the link reaction?

Answer 9

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

Question 10

Where does the link reaction take place?

Answer 10

Matrix of the Mitochondria

Question 11

What is the yield from 1 pyruvate after the link reaction?

Answer 11

• One molecule of NADH
• One molecule of Acetyl CoA
• One molecule of CO2

Question 12

What is the significance of the Krebs Cycle?

Answer 12

• It breaks down macromolecules into smaller ones
• It produces Hydrogen atoms that are carried by NAD to the electron transfer chain and provide energy for oxidative phosphorylation leading to the production of ATP.
• It regenerates the 4-Carbon molecule that combines with Acetyl CoA which would otherwise accumulate.
• It is a source of intermediate compounds used by cells in the manufacture of other important substances such as fatty acids, amino acids and chlorophyll.

Question 13

Where does the Krebs Cycle take place?

Answer 13

Matrix of the Mitochondria

Question 14

What is the yield of the Krebs Cycle per pyruvate molecule?

Answer 14

• three molecules of NADH
• one molecule of FADH
• one molecule of ATP
• three molecules of CO2

Question 15

Why is NAD important in respiration?

Answer 15

It works with dehydrogenase enzymes that catalyse the removal of hydrogen atoms from substrates and transfer them to other molecules involved in oxidative phosphorylation.

Question 16

Where does oxidative phoshorylation take place?

Answer 16

Within the inner folded membrane (cristae)

Question 17

In which cells are there more mitochondria?

Answer 17

Muscles, liver and epithelial cells. The mitochondira in these cells also have more densely packed cristae.

Question 18

How are lipids respired?

Answer 18

• Lipids are first hydrolysed to glycerol and fatty acids
• The glycerol is then phosphorylated and converted to triose phosphate which enters the glycolysis pathway and then the subsequently Krebs Cycle.
• The fatty acids is broken down into 2 - carbon fragments which are converted to Acetyl CoA. This then enters the Krebs Cycle.

Question 19

How are proteins respired?

Answer 19

• Protein is first hydrolysed to its constituent amino acids.
• These have their amino group removed (deamination) before entering the respiratoy pathway at different points depending on the number of carbon atoms they contain.
• 3-carbon compounds are converted to pyruvate, while 4-carbon and 5-carbon compounds are converted to intermediates in the Krebs Cycle.