B12 - Respiration

Question 1

What are the uses of ATP?

Answer 1

Transporting substances across the cell membrane, e.g. active transport
Movement
Maintaining body temperature

Question 2

What are coenzymes and what are examples in respiration?

Answer 2

A coenzyme is a molecule that helps an enzyme carry out its function, but is not used in the reaction itself

Coenzyme A supplies the acetyl group
NAD accepts 1 hydrogen atom
FAD accepts 2 hydrogen atoms

Question 3

Where does glycolysis take place?

Answer 3

The cytoplasm of a cell

Question 4

What happens in the first step of glycolysis (Phosphorylation) ?

Answer 4

Glucose is phosphorylated by 2 ATP molecules to form fructose bisphosphate. Glucose + 2 ATP = Fructose Bisphosphate

Question 5

What happens in the second step of glycolysis (Lysis) ?

Answer 5

Fructose Bisphosphate contains 6 carbons and is unstable so splits into 2 molecules of Triose Phosphate (TP). Fructose Bisphosphate = 2 Triose Phosphate

Question 6

What happens in the third step of glycolysis (Oxidation) ?

Answer 6

Hydrogen is removed from each molecule of triose phosphate (3C), and transferred to coenzyme NAD which forms 2 reduced NADH. 4H + 2NAD → 2NADH + 2H+

Question 7

What happens in the fourth step of glycolysis (Dephosphorylation) ?

Answer 7

Phosphates are transferred from the intermediate substrate molecules, to form 4 ATP through substrate-linked phosphorylation - 4Pi + 4ADP → 4ATP

Question 8

What happens in the last step of glycolysis (Pyruvate) ?

Answer 8

Triose Phosphate = Pyruvate (3C)

Question 9

What happens in the link reaction?

Answer 9

When oxygen is available, pyruvate moves across the double membrane by active transport, and enters the mitochondrial matrix and aerobic respiration continues

• Pyruvate is oxidised by enzymes which produces acetate and carbon dioxide. NAD is reduced here to produce NADH
• Acetate combines with Coenzyme A to form acetyl coenzyme A (acetyl CoA)

Overall Acetyl coenzyme A, carbon dioxide and NADH are formed per pyruvate molecule

Question 10

What happens in the first step of the Krebs cycle?

Answer 10

Acetyl CoA enters from link reaction, oxaloacetate (4C) accepts the 2C acetyl fragment (from acetyl CoA) and forms Citrate (6C). CoA is released and reused

Question 11

What happens in the second step of the Krebs cycle?

Answer 11

Citrate is converted back into oxaloacetate by first, Citrate being decarboxylated and CO2 released as a waste product. It is then oxidised which releases Hydrogen atoms which reduce NAD and FAD. A phosphate group is transferred from one of the intermediates to ADP to form ATP
For each molecule of acetyl CoA: 2xCO2 are released, 3xNADH are formed, 1xFADH2 is formed and 1x ATP is formed

Question 12

What happens in Oxidative phosphorylation + ATP synthesis?

Answer 12

• H+ ions & electrons (from the krebs cycle) are donated by reduced NAD & FAD
• High-energy electrons enter the chain and release energy as they are passed from protein to protein
• This energy is used to transport H+ ions into the intermembrane space
• H+ ions are pumped back into the matrix via facilitated diffusion through ATP synthase
• ATP is synthesised
• Oxygen acts as a ‘final electron acceptor’, combining with H+ ions to form water

Question 13

What happens in ethanol fermentation?

Answer 13

It is done by yeast and other microorganisms

1. Pyruvate is decarboxylated to ethanal (+ produced CO2)
2. Ethanal is reduced to ethanol (by alcohol dehydrogenase - enzyme)

Question 14

What happens in lactate fermentation?

Answer 14

Other microorganisms & mammalian muscle cells use this process

1. Reduced NAD transfers its hydrogens to pyruvate
2. Pyruvate is reduced to lactate (by lactate dehydrogenase - enzyme)