16 Respiration

Question 1

Mitochondria

Structure of membrane → Function

Answer 1

1. Outer & inner membrane permeable to Pyruvate
   i. enables Pyruvate from Glycolysis in cytosol to be used for Link Reaction in mitochondria
2. Highly convoluted ie. folded to from cristae
   i. ↑ SA for embedment of ↑ e^-carriers for ETCs & ATP Synthase
   ii. maximises rate of cellular respiration by ↑ ATP per unit time in OP
3. Mitochondrial outer membrane permeable to ATP & ADR
   i. ATP generated exits mitochondria rapidly for use in cellular activities
4. Mitochondrial inner membrane impermeable to H+ (hydrophobic core repels H+)
   i. proton gradient can be generated → chemiosmosis can occur

Question 2

Mitochondria

Structure of matrix → Function

Answer 2

1. Narrow fluid-filled intermembrane space
   i. enables formation of proton gradient for chemiosmosis by holding H⁺ that are pumped out of matrix during e^- transport
2. Mitochondria matrix, a gel-like, enzyme-containing substance
   i. enables the catalysis of reactions in LR & Krebs cycle by enzymes
3. Compartmentalisation of matrix by inner phospholipid membrane
   i. maintains ↑ enzyme concentration in matrix → ↑ ROR

Question 3

Aerobic Respiration

Definition

Answer 3

A series of enzyme-catalyses redox reactions that oxidises respiratory substrates like glucose into CO₂ while O₂ is reduced into H₂O

Question 4

Aerobic Respiration

Stage 1: Glycolysis (within Cytosol) → Phosphorylation of Glucose

Answer 4

1. 2 ATPs hydrolysed into 2 ADPs & 2 Ps
2. Each glucose is phosphorylated x2 to form fructose-1,6-biphosphate
   → C₆H₁₂O₆ is activated ie. ↑ reactive & committed to the pathway + (-)-vely charged ∴ impermeable & cannot diffuse across cell surface membrane ie. trapped within cytosol
3. Phosphofructokinase (PFK), an allosteric enzyme, catalyses the 2nd phosphorylation
   → PFK is inhibited by excess ATP/ citrate ie. end-product/ allosteric inhibition vs. stimulated by AMP/ ADP (allosteric activators)

Question 5

Aerobic Respiration

Stage 1: Glycolysis (Cytosol) → Lysis of fructose-1,6-biphosphate

Answer 5

Frustose-1,6-biphosphate is cleaved into 2 glyceraldehyde-3-phosphate (G3P) & dihydroxyacetone phosphate, an isomer of G3P through an isomerase.

where G3P = triose phosphate (TP) or phosphoglyceraldehyde (PGAL)

G3P is favoured since it is constantly removed by oxidative dehydrogenation

Question 6

Aerobic Respiration

Stage 1: Glycolysis (Cytosol) → Oxidative Dehydrogenation

Answer 6

1. Each G3P is [O] via dehydrogenation ie. removal of H while NAD⁺ is [R] to 2 NADH
2. G3P is phosphorylated to form 1,3-biphosphoglycerate

where NAD⁺ = nicotinamide adenine dinucleotide, NADH = [R] ‘’

Question 7

Aerobic Respiration

Stage 1: Glycolysis (Cytosol) → Substrate-level phosphorylation

Answer 7

1. 1,3-biphosphoglycerate is dephosphorylated x2 to form pyruvate with GP as an intermediate
2. 2 Pi transferred by enzymes to 2 ADP to form 2 ATP ie. substrate-level phosphorylation
3. 4 ATP & 2 NADH is yielded
4. Nett gain of 2 ATP & 2 NADH

Equation: C₆H₁₂O₆ + 2 ADP + 2 Pi + 2 NAD⁺ → 2 Pyruvate + 2 ATP + 2 NADH

where GP = glycerate phosphate

Question 8

Aerobic Respiration

Significance of Stage 1: Glycolysis

Answer 8

1. Can occur without O₂ to yield 2 pyruvate molecules per C₆H₁₂O₆ that can be used in both Aerobic & Anaerobic Respiration
2. Yields NADH that acts as mobile e^- carriers for ETC in OP

Question 9

Aerobic Respiration

Stage 2: Link Reaction ie. [O] Decarboxylation (Mitochondria Matrix)

Answer 9

1. Each pyruvate is decarboxylated ie. removal of C through the loss of CO₂
2. Oxidative dehydrogenation occurs to yield a 2C compound & NADH
3. 2C compound combines with coenzyme A to yield acetyl-CoA that moves into Krebs Cycle

Equation: 2 pyruvate → 2 acetyl-CoA + 2 NADH + 2 CO₂

Question 10

Aerobic Respiration

Stage 3: Krebs Cycle

Answer 10

1. Each Acetyl-CoA (2C) combines with oxaloacetate (4C) to form citrate (6C)
2. Citrate undergoes oxidative decarboxylation x2 ie. decarboxylation & oxidative dehydrogenation to form α-ketoglutarate (5C) & NADH → Succinyl-CoA
3. Succinyl-CoA transfers a Pi to ADP to form Succinate & ATP through substrate-level phosphorylation
4. A coenzyme, FAD is [R] to yield FADH₂ while substrate is [O]
5. 2x NAD is [R] to yield NADH, regenerating oxaloacetate.

where FAD = Flavin Adenine Dinucleotide

Question 11

Aerobic Respiration

Stage 4: Oxidative Phosphorylation (OP) → Electron Transport Chain (ETC)

Answer 11

1. NADH & FADH2 from Krebs cycle is [O] to NAD & FAD
2. e^- released from the [O] process flow down the ETCs across e^- carriers of increasing electronegative & progressively lower energy levels
3. O₂ acts as the final e^- acceptor in the ETC & combines with H⁺ to form H₂O.

Question 12

Aerobic Respiration

Stage 4: Oxidative Phosphorylation (OP) → Chemisosmosis

Answer 12

1. H⁺ released from the [O] process of NADH & FADH2 are pumped across the matrix to the intermembrane space using energy generated from the ETC
2. H⁺ accumulate in the intermembrane space, generating a proton gradient and thus a proton motive force
3. H⁺ diffuses through ATP synthase from the intermembrane space to the matrix & ADP is phosphorylated to form ATP ie. chemisosmosis occurs

Question 13

Anaerobic Respiration

Alcoholic Fermentation in plants & yeast

Answer 13

1. Pyruvate decarboxylase converts pyruvate into ethanal/ acetaldehyde, CO2 released ie. decarboxylation occurs
2. Alcohol dehydrogenase [R] ethanal to ethanol & NADH to NAD⁺
3. Since NAD⁺ is regenerated, Glycolysis can proceed

Question 14

Anaerobic Respiration

Lactic Acid Fermentation

Lactate = ionised Lactic Acid

Answer 14

Pyruvate is [R] to lactate by lactate dehydrogenase while NADH is [O] to NAD. Glycolysis can proceed.

Accumulation of lactic acid causes fatigue and must be converted back in the liver cells to pyruvate for use in LR and Krebs cycle.