5 Energy transfer: 12 Respiration

Question 1

What does respiration produce?

The main purpose.

Answer 1

ATP.

Question 2

What is glycolysis?

Answer 2

The first stage of anaerobic and aerobic respiration.

Question 3

Where does glycolysis occur?

Answer 3

Cytoplasm.

Question 4

Is glycolysis an aerobic or anaerobic process?

Answer 4

Anaerobic.

Question 5

What are the stages of glycolysis?

Overview

Answer 5

1. Phosphorylation of glucose to glucose phosphate, using ATP.
2. Production of triose phosphate.
3. Oxidation of triose phosphate to pyruvate with a net gain of 2 ATP and 2 reduced NAD.

Question 6

What happens to pyruvate in anaerobic respiration?

Answer 6

Pyruvate can be converted to ethanol or lactate using reduced NAD.
The oxidised NAD produced can be used in further glycolysis.

Question 7

What happens to pyruvate in aerobic respiration?

Where does it go after glycolysis and how?

Answer 7

Pyruvate from glycolysis enters the mitochondrial matrix by active transport.

Question 8

What is the process of aerobic respiration?

Answer 8

1. Pyruvate is oxidised to acetate, producing reduced NAD.
2. The link reaction: acetate combines with coenzyme A to produce acetylcoenzyme A.
3. Acetylcoenzyme A reacts with a four-carbon molecule, releasing coenzyme A, and producing a six-carbon molecule which enters the Krebs cycle.
4. The Krebs cycle generates reduced NAD/ FAD and ATP by substrate-level phosphorylation, losing CO2 in a series of oxidation-reduction reactions.
5. Synthesis of ATP (by oxidative phosphorylation) is associated with the electron transfer chain and passage of protons across inner mitochondrial membranes. This is catalysed by ATP synthase (chemiosmotic theory).
6. Other respiratory substrates, including the breakdown products of lipids and amino acids, enter the Krebs cycle.

Question 9

What are the stages of aerobic respiration?

Give overviews of each stage as well.

Answer 9

1. Glycolysis: 6-carbon glucose molecule is split into two 3-carbon pyruvate molecules.
2. Link reaction: the 3-carbon pyruvate molecules enter a series of reactions to form the 2-carbon acetylcoenzyme A.
3. Krebs cycle: acetylcoenzyme A enters a cycle of oxidation-reduction reactions that yield some ATP and a lot of reduced NAD/ FAD.
4. Oxidative phosphorylation: electrons and reduced NAD/ FAD from the Krebs cycle are used to synthesise ATP with water produced as a by-product.

Question 10

What is the process of glycolysis?

Answer 10

1. Phosphorylation of glucose: a 6C glucose is phosphorylated to glucose phosphate, using inorganic phosphates from the hydrolysis of two ATP molecules.
2. Splitting of the glucose phosphate: the glucose molecule is split into two 3C triose phosphate molecules.
3. Oxidation of triose phosphate: 2H is removed from each triose phosphate molecule and reduces NAD to form reduced NAD.
4. Production of ATP: the two triose phosphate molecules are converted to 3C pyruvate molecules. Two ATP is resynthesised for each conversion.

Question 11

What are the yields of glycolysis?

Answer 11

• two ATP molecules
• two reduced NAD molecules
• two pyruvate molecules

Question 12

What is the process of the Link reaction?

Answer 12

1. Pyruvate molecules from glycolysis are actively transported to the mitochondrial matrix.
2. Pyruvate is oxidised to acetate; it loses a CO2 and 2H which are accepted by NAD to form reduced NAD.
3. The 2C acetate combines with coenzyme A to form acetylcoenzyme A.

Question 13

What is the overall equation of the Link reaction?

Answer 13

pyruvate + NAD + CoA -> acetyl CoA + reduced NAD + CO2

Question 14

How many times do the Link reaction and Krebs cycle occur for every glucose molecule?

Answer 14

Twice, because two 3C pyruvate molecules were produced for every glucose molecule in glycolysis.

Question 15

Where does the Krebs cycle take place?

Answer 15

Mitochondrial matrix.

Question 16

What is the process of the Krebs cycle?

Answer 16

1. 2C acetyl CoA from the link reaction combines with a 4C molecule to produce a 6C molecule.
2. CoA goes back to the link reaction to be used again.
3. The 6C molecule loses 2 CO2 molecules and hydrogen to form a 4C molecule again. The hydrogen is used to reduce NAD and FAD.
4. One ATP molecule is produced due to substrate-level phosphorylation (when a phosphate group is directly transferred from one molecule to another).

Question 17

Where does oxidative phosphorylation occur?

Answer 17

Mitochondria.

Question 17

What does oxidative phosphorylation involve?

Answer 17

The electron transport chain and chemiosmosis.

Question 18

What is the process of oxidative phosphorylation?

Answer 18

1. H atoms are released from reduced NAD/FAD (which are therefore oxidised).
2. The H atoms are split into protons and electrons.
3. The electrons move down the elctron transport chain, losing energy at each carrier.
4. The lost energy is used to pump protons from the mitochondrial matrix into the intermembrane space.
5. Concentration of protons is now higher in the intermembrane space than in the mitochondrial matrix, forming an electrochemical gradient (conc gradient of ions).
6. Protons therefore move down the electrochemical gradient, from the intermembrane space to the mitochondrial matrix, via ATP synthase.
7. This movement of protons drives the synthesis of ATP from ADP and Pi.
8. At the end of the electron transport chain, the protons, electrons, and O2 (from the blood) combine to form water.
9. Oxygen is the final electron acceptor.

Question 19

How can mitochondrial diseases affect ATP production?

Answer 19

They can affect how proteins involved in oxidative phosphorylation or the Krebs cycle function, reducing ATP production.
This may cause anaerobic respiration to increase, resulting in a lot of lactate being produced.

Question 20

What does high lactate concentration in the body cause?

Answer 20

Muscle fatigue and weakness.

Question 21

What molecules, other than glucose, can be used as respiratory substrates?

Answer 21

Fatty acids from lipids and amino acids.