3.5.1 Respiration

Question 1

4 stages of aerobic respiration

Answer 1

• glycolysis
• link reaction
• Krebs cycle
• oxidative phosphorylation

Question 2

Where does glycolysis occur?

Answer 2

cytosol in cytoplasm (glucose is split as too large to get into mitochondria)

Question 3

Summarise stages of glycolysis

Answer 3

• glucose (6C) phosphorylated twice using 2 ATP
• producing hexose diphosphate (6C)
• This then splits into 2 TP molecules (3C)
• TP undergoes dehydrogenation and is OXIDISED to form 2 pyruvate (3C)
• Oxidation of TP (removing H+ and e- that are picked up by NAD) forms 2 NADH
• substrate level phosphorylation occurs ( 4 ADP +Pi -> 4 ATP)

Question 4

Glycolysis - products per glucose molecule

Answer 4

• 2 pyruvate (3C)
• 2 NADH
• 2 NET ATP (4 total)

Question 5

Where does link reaction occur?

Answer 5

mitochondrial matrix

Question 6

How many times does link reaction occur?

Answer 6

twice per glucose molecule - 2 simultaneous reactions as there are 2 pyruvate molecules made in glycolysis

Question 7

Summarise stages of link reaction

Answer 7

• pyruvate (3C) is oxidised (dehydrogenation by dehydrogenase) - H+ and e- are removed
• NAD is reduced to NADH
• CO2 is removed from pyruvate (decarboxylation)
• to form acetate (2C)
• Coenzyme A combined with acetate forming acetyl CoA

Question 8

Link reaction - products per glucose molecule

Answer 8

• 2 acetyl CoA
• 2 NADH
• 2 CO2

Question 9

Where does Krebs cycle occur

Answer 9

mitochondrial matrix

Question 10

How many times does Krebs cycle occur?

Answer 10

twice per glucose molecule - for each molecule of acetyl CoA (from 2 pyruvate)

Question 11

Summarise stages of Krebs cycle

Answer 11

• Acetate (2C) combined with oxaloecetate (4C) forming a citrate molecule (6C)
• 6C oxidised - H+ and e- removed
• NAD reduced to NADH
• 6C has CO2 removed to become 5C (decarboxylation)
• 5C oxidised multiple times
• 2 NAD reduced to 2 NADH and FAD reduced to FADH
• 5C has CO2 removed becoming 4C
• substrate level phosphorylation occurs forming ATP

Question 12

Krebs cycle - products per glucose molecule

Answer 12

• 6 NADH
• 2 FADH
• 4CO2
• 2 ATP

Question 13

Where does oxidative phosphorylation occur?

Answer 13

inner mitochondrial membrane (cristae)

Question 14

Summarise stages of oxidative phosphorylation

Answer 14

• NADH and FADH from Krebs cycle split into high energy electrons, H+ and NAD/FAD
• energy from electrons powers electron carrier to pump protons (H+) from the matrix into the inter membrane space
• creating a proton gradient
• protons flow down gradient through ATP synthase (chemiosmosis)
• resulting in phosphorylation of ADP to ATP (ADP + Pi-> ATP)

Question 15

Describe how ATP is made in mitochondria

Answer 15

• 2 NAD -> 2 NADH
• FAD -> FADH
• substrate level phosphorylation occurs - ATP formed
• NADH and FADH from Krebs cycle split into high energy electrons, H+ and NAD/FAD
• energy from electrons powers electron carrier to pump protons (H+) from the matrix into the inter membrane space
• creating a proton gradient
• protons flow down gradient through ATP synthase (chemiosmosis)
• resulting in phosphorylation of ADP to ATP (ADP + Pi-> ATP)

Question 16

in a glucose shortage what other molecules are used as respiratory substances?

Answer 16

lipids and proteins

Question 17

How are lipids broken down for respiration?

Answer 17

• glycerol is covered to TP (3C) - glycolysis intermediate
• long fatty acid chains are split into 2C fragments which enter the pathways as acetyl CoA (this generates lots of ATP as the chains are long)