Chapter 18 Respiration

Question 1

Describe the structure of mitochondria.

Answer 1

Mitochondria has a double membrane. There is the outer membrane, which has a role of compartmentalisation. The inner membrane is highly folded to form a structure called cristae. The cristae contains proteins for the electron transport chain. As the cristae is folded, this also means it has a large surface area for oxidative phosphorylation. The area of space between the outer and inner membrane is called the intermembrane space. The space within the cristae is called the matrix, which contains enzymes and mitochondrial DNA.

Question 2

State the stages of aerobic respiration.

Answer 2

Glycolysis.
Link Reaction.
Krebs cycle.
Electron transport chain.

Question 3

State the stages of anaerobic respiration in mammals and yeast.

Answer 3

In mammals> glycolysis which produces lactate.
In yeast> Glycolysis which produces ethanol and carbon dioxide (fermentation).

Question 4

Where does the first stage of respiration take place and is oxygen needed?

Answer 4

Glycolysis takes place in the cytoplasm of the cell and no oxygen is needed.

Question 5

In glycolysis, glucose is first phosphorylated. What does it require and what is produced through phosphorylation?

Answer 5

To phosphorylate glucose, 2 ATP molecules are required (which turns into 2 ADP), and it produces hexose bisphosphate.

Question 6

In glycolysis, hexose bisphosphate splits to form 2 triose phosphate. After this, how is each triose phosphate converted to triose bisphosphate?

Answer 6

Each triose phosphate is phosphorylated again to form 2 triose bisphosphate. This phosphorylation does not require ATP molecules but is brought about by inorganic phosphate ions in the cytoplasm.

Question 7

In glycolysis, how is triose bisphosphate converted to pyruvate?

Answer 7

In each compound of triose phosphate, there are 2 phosphate ions present. Each triose bisphosphate gets their phosphate ions (2 Pi) taken from them by 2 ADP molecules. These 2 ADP molecules are converted to 2 ATP molecules through the taking of phosphate ions from triose bisphosphate. The taking of 2 phosphate ions converts triose bisphosphate to pyruvate.
Additionally, each triose bisphosphate is oxidised by the removal of hydrogen atoms (dehydrogenation). The removal of these hydrogen atoms are donated to the coenzyme NAD to form reduced NAD (NADH).

Question 8

The conversion of triose bisphosphate to pyruvate is described as substrate level phosphorylation. Why is this?

Answer 8

In the conversion of triose bisphosphate to pyruvate, 4 ATP molecules are formed (2 from each triose bisphosphate molecule). It is substrate level phosphorylation as this is the production of ATP without the use of an electron transport chain and ATP synthase. ADP is phosphorylated by an unstable intermediate to form ATP.

Question 9

What are the products of the glycolysis stage in respiration?

Answer 9

2 pyruvate molecules.
Net gain of 2 ATP molecules.
2 reduced NAD molecules.

Question 10

Where does the Link reaction take place?

Answer 10

In the mitochondrial matrix.

Question 11

How does products of glycolysis go from the cytoplasm into the mitochondrial matrix?

Answer 11

The products, pyruvate, enters the mitochondrial matrix through active transport via specific carrier proteins in the mitochondrial membrane.

Question 12

In order to form the acetyl group from pyruvate in the Link reaction, the pyruvate is said to have undergone ‘oxidative decarboxylation’. Why is this?

Answer 12

‘Decarboxylation’- Removal of carbon dioxide from pyruvate (a carbon is removed to give a 2-carbon molecule- the acetyl).
‘Oxidative’- Pyruvate loses a hydrogen, and hence, is oxidised. This hydrogen is accepted by NAD to form NADH.

Question 13

What is the final product of the Link reaction?
How does the intermediate, the acetyl group, form this?

Answer 13

The final product of the Link reaction is acetylCoenzyme A. It is formed when the acetyl group bonds with Coenzyme A, to temporarily stabilise the structure so acetylCoenzyme A can carry the acetyl group to the next stage, the Kreb’s cycle.

Question 14

The first intermediate of the Kreb’s cycle is citrate (citric acid). How is it formed?

Answer 14

The acetyl group, from acetylCoenzyme A of the Link reaction, is donated into the Kreb’s cycle. It reacts with a 4-carbon molecule, oxaloacetate, to form citric acid (which is 6 carbon).

Question 15

After citrate is formed in the Kreb’s cycle, the citrate forms a 5 carbon intermediate. This 5 carbon intermediate then goes to form a 4 carbon intermediate. Through what processes are these intermediates formed?

Answer 15

To form the 5 carbon intermediate and 4 carbon intermediate, dehydrogenation and decarboxylation occurs.
Dehydrogenation- The intermediate loses a hydrogen atom, in which NAD accepts to form NADH.
Decarboxylation- The intermediate loses a carbon dioxide.

Question 16

After the 4 carbon molecule is formed in the Kreb’s cycle, it then goes on to forming oxaloacetate. Through what processes is oxaloacetate formed?

Answer 16

Oxaloacetate is formed through dehydrogenation and substrate level phosphorylation.
Dehydrogenation- This happens twice. Oxaloacetate loses 2 hydrogens in which FAD accepts to form red FAD. Oxaloacetate then loses a hydrogen, in which NAD accepts to form NADH.
Substrate level phosphorylation- ATP is produced from ADP and Pi. Although, no electron transport chain is required and no ATP synthase is required.

Question 17

Why is oxaloacetate formed as the last product of the Kreb’s cycle?

Answer 17

It allows oxaloacetate to enter the cycle again, to react with another acetyl group, to form more reduced enzymes.

Question 18

State the importance of coenzymes in respiration.

Answer 18

Without coenzymes (FAD and NAD), no electrons and protons could be available to be available during respiration, especially during stage 4, oxidative phosphorylation. This stage relies on the generation of electrons and protons from these reduced enzymes in order for chemiosmosis to occur to form ATP.

Question 19

State differences between coenzymes NAD and FAD.

Answer 19

NAD- Takes place in all stages of cellular respiration.
FAD- Only produced in Kreb’s cycle and used in oxidative phosphorylation.
….
NAD- Accepts 1 hydrogen atoms.
FAD- Accepts 2 hydrogen atoms.
….
NAD- Oxidised at the start of electron transport chain.
FAD- Oxidised further along electron transport chain.
….
NAD- Red NAD results in synthesis of 3 ATP molecules.
FAD- Red FAD results in synthesis of 2 ATP molecules.

Question 20

Where does the Kreb’s cycle occur?

Answer 20

Mitochondrial matrix.

Question 21

Where does oxidative phosphorylation occur?

Answer 21

Over inner mitochondrial membrane- cristae.

Question 22

In order for chemiosmosis to occur in stage 4 of respiration, electrons and hydrogen ions are required. From where are these electrons and hydrogen ions produced from?

Answer 22

Reduced enzymes produced in the last 3 stages releases electrons and hydrogen ions for chemiosmosis to occur.

Question 23

Describe the movement of electrons in the electron transport chain in the inner mitochondrial membrane of stage 4 of respiration.

Answer 23

When the electrons are first released from the reduced enzymes, they have very high energy- they are excited. These electrons enters the electron transport chain in the membrane and the movement of electrons along the electron carriers causes them to release energy. Due to the release of energy, by the end, the electrons have low energy.

Question 24

How are hydrogen ions able to move from the mitochondrial matrix into the intermembrane space?

Answer 24

Protein pumps in the inner mitochondrial membrane uses the energy released by the movement of electrons in the electron transport chain, to actively transport/pump hydrogen ions from the mitochondrial matrix into the intermembrane space.

Question 25

What does the movement of hydrogen ions from the mitochondrial matrix into the intermembrane space cause?
How does it result in the formation of ATP?

Answer 25

The movement of hydrogen ions from mitochondrial matrix to intermembrane space establishes a proton gradient.
The proton gradient makes the protons want to diffuse back into the mitochondrial matrix. It does so through facilitated diffusion- it travels through a protein in the membrane, ATP synthase. The movement of protons through ATP synthase drives ADP and a phosphate ion closer together to form ATP.

Question 26

Define fermentation.

Answer 26

The breakdown of molecules into smaller molecules without using oxygen.

Question 27

In what organisms does lactate fermentation occur?
Is it a reversible process?

Answer 27

Lactate fermentation occurs in animals.
It is a reversible process.

Question 28

In what organisms does alcoholic fermentation occur?
Is it a reversible process?

Answer 28

Alcoholic fermentation occurs in yeast.
It is not a reversible process.

Question 29

What is the first stage of any type of fermentation (lactate or alcoholic)?

Answer 29

The first stage of any type of fermentation is glycolysis, where pyruvate is formed.

Question 30

In lactate fermentation, lactate is produced from pyruvate. How does this occur?

Answer 30

A reduced NAD is oxidised as it donates a hydrogen atom to the pyruvate molecule (and hence the pyruvate is reduced), to give just NAD and the lactate. This process occurs in the presence of the enzyme lactate dehydrogenase.

Question 31

Glucose can be formed in lactate. Where does this occur, and how does this occur?
Why cannot lactate stay to exist in cells after it is produced as a result on anaerobic respiration?

Answer 31

The lactate is transported through the bloodstream to the liver, where it reacts with an oxygen debt in the liver to produce glucose.
Lactate is basically lactic acid; if the lactic acid stays to exist in cells, it can denature proteins in the cell due to changes in pH.

Question 32

In alcoholic fermentation, ethanal is produced from pyruvate. How does this occur?
After, ethanol is produced from ethanal. How does this occur?

Answer 32

Ethanal is produced from pyruvate through decarboxylation, which occurs in the presence of enzyme, pyruvate decarboxylase.
Ethanol is produced from ethanal, as the ethanal is reduced. The ethanal accepts a hydrogen atom from reduced NAD, in which ethanol is produced and NAD.

Question 33

How many ATP molecules does the respiration of one glucose molecule produce?

Answer 33

It produces 38 ATP molecules.

Question 34

Describe how a triglyceride can be used as a respiratory substrate.

Answer 34

The triglyceride can be broken down into a glycerol and 3 fatty acids.
Glycerol- The glycerol can be converted into pyruvate which would then enter the Link reaction, and go onto following stages.
3 fatty acids- Through beta oxidation, 3 fatty acids can form approximately 500 acetyl Coenzymes A, which then can approximately produce 500 ATP molecules.

Question 35

Compare glucose as a respiratory substrate to a triglyceride as a respiratory substrate.

Answer 35

A triglyceride has a higher energy content, producing approximately 500 ATP molecules and a pyruvate molecule (one glucose molecule only produces 38 ATP molecules). This is because the 3 fatty acids in the triglyceride has increasingly more carbon-hydrogen bonds that release energy.

Question 36

Proteins can be used as a respiratory substrate. Through what process can a pyruvate molecule be obtained from a protein?

Answer 36

The amino acids from the protein can undergo deamination in the liver to produce a pyruvate molecule.

Question 37

Why is using protein as a respiratory substrate not very ideal?

Answer 37

First, if we are using proteins to undergo deamination, we are decreasing the muscle mass in the body.
Additionally, the process of deamination to produce a pyruvate molecule actually requires energy, so there is a net loss of ATP through this process.

Question 38

How can we calculate the respiratory quotient through experimentation?

Answer 38

RQ= Vol of carbon dioxide produced / Vol of oxygen absorbed