Respiration

Question 1

What happens during energy investment phase of glycolysis

Answer 1

a. Hydrolysis of 2 ATPs to provide phosphate groups and energy / driving force

b1. Conversion of unphosphorylated glucose (6C) to phosphorylated-1,6-bisphosphate by phosphofructokinase
b2. cleavage of fructose-1,6-bisphosphate (6C) to 2 G3P (3C)

Question 2

Basic details of glycolysis

Answer 2

Location: cytosol
Rxts: 1 glucose, NAD, ADP + Pi
Pdts: 2 pyruvate, 2 ATP, 2 NADH

Question 3

Energy-payoff phase of glycolysis

Answer 3

1. (a) each G3P is oxidised and
   (b) NAD is reduced to NADH
2. (a) dephosphorylation of G3P (3C) to form pyruvate (3C) and
   (b) substrate-level phosphorylation of 2 ADP to 2 ATP

Question 4

Basic details of Link Reaction

Answer 4

Location: mitochondrial matrix
Rxts: Pyruvate, NAD, Coenzyme A
Pdts: 2 Acetyl CoA, 2 NADH, 2 CO2

Question 5

Process of link reaction

Answer 5

1. Pyruvate (3C) undergoes decarboxylation (becomes 2C), where its carboxyl grp is removed and liberated as CO2
2. (a) Remaining 2C fragment is oxidised to form acetate (2C),
   (b) and NAD is reduced to NADH
3. Coenzyme A attaches to acetate (2C), forming acetyl CoA (2C)

Question 6

Basic details of Krebs/Citric acid cycle

Answer 6

Location: mitochondrial matrix
Rxts: acetyl CoA, NAD, FAD, ADP + Pi
Pdts: 4 CO2 (waste pdt), 6 NADH, 2 FADH2, 2 ATP

Question 7

Process of citric acid cycle

Answer 7

1. Acetyl CoA (2C) combines with oxaloacetate (4C) to form citrate (6C)
2. Oxaloacetate is regenerated and recycled to bind to another acetyl CoA group and repeat the process

During regeneration of oxaloacetate:
1. oxidative decarboxylation occurs 2 times, where its carboxyl grp is removed and liberated as CO2

2. production of reduced coenzymes by dehydrogenation,
   (a) where substrate is oxidised
   (b) and NAD and FAD is reduced to NADH and FADH2
3. (a) dephosphorylation of intermediate and
   (b) substrate-level phosphorylation of ADP to ATP (with GTP as intermediate)

Question 8

Basic details of oxidative phosphorylation

Answer 8

Location: inner mitochondrial membrane
Rxts: NADH and FADH2
Pdts: ATP

Question 9

Process of oxidative phosphorylation

Answer 9

1. Electron transport
   - sequence of electron carriers are reversible reduced and oxidised as electrons from NADH and FADH2 are passed down mitochondrial ETC
   => NAD and FAD are regenerated in the process
   - electrons are passed down to the
   final electron acceptor, oxygen,
   which is reduced in the mitochondrial matrix
   to produce a molecule of water
2. Chemiosmosis
   - energy released during e- transport drives proton pumps
   to actively pump H+ unidirectionally
   across inner mitochondrial membrane
   from mitochondrial matrix to intermembrane space
   - thus proton gradient is generated
   - and due to the tendency for H+ to diffuse back into the matrix, proton motive force is generated

ATP synthesis
1. protons diffuse down concentration gradient to re-enter matrix via ATP synthase
(as mitochondrial membrane is impermeable to H+)
2. thus rotating ATP synthase
3. and allowing the synthesise of ATP from ADP and Pi

Question 10

Lactic acid fermentation

Answer 10

Location: cytosol
Process:
(a) pyruvate (3C) reduced to form lactate (2C)
(b) as NADH is oxidised to regenerate NAD

Question 11

Alcoholic fermentation

Answer 11

Location: cytosol
Process:
1. CO2 is released from pyruvate (3C) as it is converted to acetaldehyde (2C)
2. (a) acetaldehyde (2C) is then reduced by NADH to ethanol (2C)
(b) as NADH is oxidised to regenerate NAD

Question 12

Elaboration on electron flow (in respiration)

Answer 12

• Membrane proteins grouped into complexes I, II, III, IV in the ETC and function as electron carriers
• ETC is arranged in increasing electron affinity
• thus ensuring flow of electrons down ETC is unidirectional
• NADH and FADF2 are then reoxidised, donating electrons
• which are then passed down electron carriers through a series of redox reactions

Question 13

Similarities between aerobic and anaerobic respiration

Answer 13

Similarities:
- process
- glycolysis
- substrate
- where 1 molecule of glucose is broken down to 2 molecules of pyruvate and 2 ATP and 2 NADH
- product
- reduction of NAD to NADH as coenzymes
- 2 ATP is released via substrate-level phosphorylation
- location
- occurs in cytoplasm
- detail
- enzyme-catalysed reaction

Question 14

Differences between aerobic and anaerobic respiration

Answer 14

• location
  
  • aerobic resp occurs in cytoplasm and mitochondria, while anaerobic resp occurs only in cytosol
• process
  
  • aerobic resp occurs in the presence of oxygen while anaerobic resp occurs in the absence of oxygen
  • aerobic resp involves glycolysis, link rxn, Krebs cycle and oxidative phosphorylation, while anaerobic resp only involves glycolysis
  • oxygen is the final e- acceptor in aerobic resp, while pyruvate is the final e- acceptor in anaerobic resp
  • aerobic resp produces ATP by substrate-level and oxidative phosphorylation, while anaerobic resp produces ATP by only substrate-level phosphorylation
• product
  
  • aerobic resp releases 36/38 ATP per molecule of glucose while anaerobic rep only releases 2 ATP per molecule
  • CO2 and H2O are pdts of aerobic resp while lactate/ethanol are pdts of anaerobic resp
• NADH
  
  • aerobic resp involves the use of NADH and FADH while anaerobic resp only involves the use of NADH
  • NADH is used in aerobic resp to transfer high-energy e- to the ETC for oxidative phosphorylation,
    while NADH is used in anaerobic resp to reduce pyruvate to lactate/ethanol to allow anaerobic resp to continue

Question 15

role of NAD

Answer 15

• coenzyme
• which carries (high energy) electrons and protons
• to ETC
• through redox reaction