Aerobic And Anaerobic Respiration

Question 1

How many ATP molecules are formed at the end of glycolysis?

Answer 1

2 molecules of ATP

Question 2

What happens in stage one of glycolysis?

Answer 2

• Phosphorylation
• Glucose is phosphorylated by adding 2 phosphates from 2 molecules of ATP
• This forms 2 molecules of triose phosphate, a three carbon compound, and 2 molecules of ADP

Question 3

What happens in the second stage of glycolysis?

Answer 3

• Oxidation
• Triose phosphate is oxidised (releasing hydrogen)and forms 2 molecules of pyrauvate, a three carbon compound
• NAD is reduced by the hydrogen given off in the oxidation of triose phosphate to form reduced NAD
• 4 ATP are produced but 2 are used in stage 1

Question 4

Where does glycolysis take place?

Answer 4

In the cytoplasm of a cell, in the sarcoplasm in muscle cells

Question 5

What are the start and end products of glycolysis?

Answer 5

1 molecule of glucose —> 2 molecules of

                                                 pyrauvate

Question 6

Why must energy first be put into the breakdown of glucose?

Answer 6

Glucose is quite stable and​ unreactive

Question 7

What is NAD?

Answer 7

A coenzyme

Question 8

What is it called when a phosphate from the intermediate compound in glycolysis is transferred to ADP, forming ATP?

Answer 8

Substrate-level phosphorylation

Question 9

Why are the glycolysis reactions described as anaerobic whether they are occuring under aerobic or anaerobic conditions?

Answer 9

No oxygen used in the reactions

Question 10

If 60000 glucose molecules undergo glycolysis:

a. How many molecules of ATP would be produced in total?
b. What would be the net gain of ATP?

Answer 10

a. 240,000

b. 120,000

Question 11

What happens to the two pyruvate molecules after they have been formed?

Answer 11

Move into the matrix of the mitochondria and used in the Link reaction

Question 12

What are the start and end molecules in the Link reaction?

Answer 12

Pyruvate —-> Acetyl coenzyme A

Question 13

Describe what happens in the Link reaction

Answer 13

• Pyruvate, a 3 carbon compound, is decarboxylated
• The carbon comes off in the form of CO2
• NAD is reduced, from the hydrogens formed by the dehydrogenation of pyruvate, to form reduced NAD
• Pyruvate is converted into acetate, a two carbon compound
• Acetate combines with coenzyme A to form acetyl coenzyme A
• No ATP produced in this reaction

Question 14

Why does the Link reaction occur twice for every glucose molecule?

Answer 14

2 pyruvate molecules made from every one molecule of glucose

Question 15

What are the end products of the Link reaction of one glucose molecule?

Answer 15

• 2 molecules of acetyl coenzyme A, a two carbon compound
• 2 molecules of CO2
• 2 molecules of reduced NAD

Question 16

Where are the two molecules of reduced NAD that are formed in the Link reaction used?

Answer 16

Oxidative phosphorylation (ATP synthesis)

Question 17

What does the Krebs cycle produce?

Answer 17

Reduced NAD, reduced FAD and ATP

Question 18

Where does the Krebs cycle take place?

Answer 18

In the matrix of the mitochondria

Question 19

How many times does the Krebs cycle happen for each molecule of glucose?

Answer 19

Twice

Question 20

Describe the Krebs cycle

Answer 20

• Acetyl coenzyme A, a two carbon compound, combines with a 4-carbon compound to form a 6-carbon compound
• Coenzyme A returns to the Link reaction to be used again
• The six carbon compound is converted to a 5 carbon compound through decarboxylation where CO2 is removed
• The six carbon compound is also dehydrogenated to give of two hydrogens
• These 2 hydrogens reduce 2 NAD to form 2 reduced NAD
• 5 carbon compound is converted into a 4-carbon compound through decarboxylation, giving off CO2
• Dehydrogenation occurs to form 2 molecules of reduced NAD and 1 molecule of reduced FAD

-ATP is produced from the transfer of a phosphate group from an intermediate compound to ADP in substrate-level phosphorylation

Question 21

What is released as the waste product of the Krebs cycle?

Answer 21

CO2 (2 molecules per cycle)

Question 22

What are the two processes in oxidative phosphorylation?

Answer 22

Electron transport chain and chemiosmosis

Question 23

Describe how the electron transport chain and chemiosmosis are involved in ATP synthesis

Answer 23

• Reduced coenzymes move to the inner membrane of the mitochondria
• Reduced coenzymes are then oxidised and release hydrogen atoms, which split into H+ ions and electrons, e-
• Electrons are past along the ETC in​a series of redox reactions, losing energy at each carrier
• This energy is used to pump H+ ions from the mitochondrial matrix to the intermembrane space, making it more positive
• The concentration of H+ ions in the intermembrane space is now higher than in the mitochondrial matrix which creates an electrochemical gradient
• H+ ions move down the electrochemical gradient back into the mitochondrial matrix through hollow protein channels
• H+ diffusion allows ATP synthase to catalyse ATP synthesis as it causes a change in shape of the enzyme’s active site which allow ADP and phosphate ions to bind to it
• Within the matrix H+ ions and electrons recombine to form hydrogen atoms which combine with oxygen to form water
• The oxygen acts as the final carrier in the ETC so is reduced

Question 24

Why is the synthesis of ATP via the electron transport chain termed ‘oxidative phosphorylation’?

Answer 24

• Oxidation-reduction reactions occur as electrons pass along the chain
• The final electron acceptor is oxygen
• Phosphate is added to ADP to form ATP

Question 25

Suggest why the Link reaction and the Krebs cycle take place inside the mitochondria?

Answer 25

Electron carriers of the ETC and ATP synthase are on the inner mitochondria membrane which allows more ATP molecules to be made as the series of steps are done in the same area instead of in different parts of the cytoplasm

Question 26

How many reduced NAD are made from one molecule of glucose?

How many are made in each place?

Answer 26

10

• 2 in glycolysis
• 2 in the Link reaction
• 6 in the Krebs cycle

Question 27

What is the maximum amount of ATP that could theoretically be made from aerobic respiration of one molecule of glucose?

Why would you not get this amount?

Answer 27

38

• Because the electrochemical gradient is also involved in the transport of other molecules such as ADP and ATP which uses H+ ions
• This means that not all H+ ions are available for the generation of ATP molecules

Question 28

What is the actual yield of ATP?

Answer 28

Around 30 ATP

Question 29

What happens to the energy that is not released by ATP?

Answer 29

Raises the temperature of the cell which increases the rate of metabolic reactions

Question 30

How is respiration controlled by ATP?

Answer 30

• ATP inhibits the enzyme in the first step of glycolysis
• In the presence of ATP the enzyme has a shape that makes it inactive
• As ATP is broken down, the enzyme is converted back to the active form
• Know as end point inhibition

Question 31

What is meant by end point inhibition?

Answer 31

The end product inhibits an early step in the metabolic pathway so the concentration of product controls the reaction

Question 32

What is the advantage of having a system of enzyme-controlled reactions to transfer energy from food fuels?

Answer 32

• Prevents cell overheating

- Allows the controlled release of energy in small, useful amounts

Question 33

What is the start, intermediate and end product in anaerobic respiration?

Answer 33

Glucose –> Pyruvate –> Lactate

Question 34

What is the yield of ATP per glucose molecule using anaerobic respiration?

Answer 34

2 ATP molecules per glucose

Question 35

Why does anaerobic respiration only last for a few seconds?

Answer 35

Because ATP runs out and can’t be replaced fast enough as the Link reaction and the Krebs cycle cannot take place without oxygen