Topic 5: Respiration

Question 1

Name 4 main stages in aerobic respiration and where they occur.

Answer 1

glycolysis: cytoplasm
link reaction: mitochondrial matrix
krebs cycle: mitochondrial matrix
oxidative phosphorylation via ETC: membrane of cristae

Question 2

Outline the stages of glycolysis

Answer 2

1. glucose is phosphorylated to glucose phosphate by 2x ATP
2. glucose phosphate splits into 2x triose phosphate
3. 2x TP is oxidised to 2x pyruvate

net gain of 2x reduced NAD and 2x ATP per glucose

Question 3

How does pyruvate from glycolysis enter the mitochondria?

Answer 3

via active transport

Question 4

What happens during the link reaction?

Answer 4

1. oxidation of pyruvate to acetate
   -Per pyruvate molecule: net gain of 1x CO2 (decarboxylation) and 2H (used to reduce 1x NAD)
2. acetate combines with coenzyme A to form acetylcoenzyme A

Question 5

What happens in the krebs cycle?

Answer 5

series of redox reactions produces:
- ATP by substrate level phosphorylation.
- reduced coenzymes
- CO2 from decarboxylation

Question 6

What is the electron transfer chain?

Answer 6

Series of carrier proteins embedded in membrane of the cristae of mitochondria. Produces ATP through oxidative phosphorylation via chemiosmosis during aerobic respiration

Question 7

what happens in the electron transfer chain?

Answer 7

electrons released from reduced NAD and FAD undergo successive redox reactions. The energy released is coupled to maintaining proton gradient or released as heat. Oxygen acts as a final electron acceptor

Question 8

How is a proton conc. gradient established during chemiosmosis in aerobic respiration?

Answer 8

some energy released from the etc is coupled to the active transport of H+ ions from the mitochondrial matrix into the intermembrane space

Question 9

Stages of glycolysis

Answer 9

1- phosphorylation of glucose to glucose phosphate. Glucose first has to be made more reactive by the addition of two phosphate molecules (phosphorylation). The phosphate molecules come from the hydrolysis of 2 ATP molecules to ADP. This provides energy to activate glucose and lowers Ea for the enzyme controlled reactions

2- Splitting of phosphorylated glucose into two 3- carbon molecules known as triose phosphate

3- Oxidation of triose phosphate. H is removed from each of the two triose phosphate molecules and transferred to a hydrogen-carrier molecule NAD to form reduced NAD

4- The production of ATP. Enzyme controlled reactions convert each triose phosphate into another 3-Carbon molecule called pyruvate. 2 molecules of ATP are regenerated from ADP

Question 10

Yield from glycolysis?

Answer 10

• 2x ATP
• 2x reduced NAD
• 2x pyruvate

Question 11

Overall equation of the link reaction?

Answer 11

pyruvate + NAD + CoA –> acetylCoA + reduced NAD + CO2

Question 12

Describe the link reaction?

Answer 12

• the pyruvate is oxidised to acetate. In this reaction, the 3-carbon pyruvate loses a carbon dioxide molecule and two hydrogens. These§ hydrogens are excepted by NAD to form reduced NAD which is later used to produce ATP.
• The 2-carbon acetate combines with a molecule called coenzyme A to produce acetylcoenzyme A

Question 13

Describe the Krebs cycle?

Answer 13

-the two carbon acetylcoenzyme A from the link reaction combines with a 4-carbon molecule to produce a 6-carbon molecule.
- in a series of reactions, the 6-C molecule loses CO2 and H to give a 4-C molecule and a single molecule of ATP as a result of substrate level phosphorylation.
- the 4-C molecule can now combine with a new molecule of acetylcoenzyme A to begin the cycle again

Question 14

For each molecule of pyruvate, the link reaction and krebs cycle produces:

Answer 14

-reduced coenzyme such as NAD and FAD
- 1x ATP
- 3CO2

Question 15

3 reasons why the krebs cycle is significant?

Answer 15

1- produces H atoms that are carried by NAD to the ETC and provide energy energy for oxidation phosphorylation. Leads to production of ATP
2- Regenerates the 4 C molecule that combines with acetylcoenzyme A which would otherwise accumulate
3- a source of intermediate compounds used by cells to manufacture of substances such as fatty acids, amino acids and chlorophyll

Question 16

Describe in detail the ETC and ATP synthesis

Answer 16

1-the H atoms produced during glycolysis and the krebs cycle combine with the coenzymes NAD and FAD
2- the reduced FAD and NAD donate the electrons of the H atoms to the first moleccule in the ETC
3- the electrons pass along a chain of electron transfer carrier molecules in a series of redox reactions. As the electrons move along the chain, the energy they release causes the active transport of protons across the inner mitochondrial membrane and into inter- membrane space
4- protons accumulate here before they diffuse bak into matrix through ATP synthase channels embedded in the inner mitochondrial membrane
5- at the end of the chain the electrons combine with these protons and oxygen to form water. Oxygen is therefore the final electron acceptor

Question 17

Overall equation for anaerobic respiration in plants

Answer 17

pyruvate + reduced NAD –> ethanol + carbon dioxide + oxidised NAD

Question 18

Overall equation for anaerobic respiration in animals

Answer 18

pyruvate + reduced NAD –> lactate + oxidised NAD