Pryruvate oxidation & Krebs Cycle

Pyruvate Oxidation Step 1

Enzyme: PDH (pyruvate dehydrogenase complex). What happens: pyruvate enters the mitochondrial matrix and its carboxyl group is removed, so CO2 is RELEASED (first CO2 of respiration). REACTION: Pyruvate (3C) to 2C fragment + CO2

Pyruvate Oxidation Step 2

Enzyme: PDH. What happens: the 2C fragment is OXIDIZED into an acetyl group, NAD+ is REDUCED to NADH. REACTION: 2C fragment + NAD+ to acetyl group + NADH + H+

Pyruvate Oxidation Step 3

Enzyme: PDH. What happens: coenzyme A (CoA) attaches to the acetyl group by its sulfur atom. REACTION: Acetyl group + CoA to acetyl-CoA

Pyruvate Oxidation: overall reaction

Pyruvate + CoA + NAD+ to acetyl-CoA + NADH + H+ + CO2 (happens x2 per glucose)

Pyruvate Oxidation: net final products

2 acetyl-CoA + 2 NADH + 2 CO2 (per glucose)

Pyruvate Oxidation: net ATP yield

0 ATP made directly. The 2 NADH give 5 ATP later in the ETC

Krebs Step 1

Enzyme: citrate synthase. What happens: the 2C acetyl group joins 4C oxaloacetate to make 6C citrate; CoA is released. REACTION: Acetyl-CoA + oxaloacetate + H2O to citrate + CoA

Krebs Step 2

Enzyme: aconitase. What happens: citrate is rearranged into its isomer isocitrate. REACTION: Citrate to isocitrate

Krebs Step 3

Enzyme: isocitrate dehydrogenase. What happens: isocitrate is OXIDIZED, NAD+ is REDUCED to NADH, and CO2 is RELEASED (6C to 5C). REACTION: Isocitrate + NAD+ to alpha-ketoglutarate + NADH + CO2

Krebs Step 4

Enzyme: alpha-ketoglutarate dehydrogenase. What happens: alpha-ketoglutarate is OXIDIZED, NAD+ is REDUCED to NADH, CO2 is RELEASED (5C to 4C), and CoA attaches. REACTION: Alpha-ketoglutarate + NAD+ + CoA to succinyl-CoA + NADH + CO2

Krebs Step 5

Enzyme: succinyl-CoA synthetase. What happens: SUBSTRATE-LEVEL PHOSPHORYLATION, CoA is released and the energy makes GTP, which makes ATP (only ATP made directly in the cycle). REACTION: Succinyl-CoA + GDP + Pi to succinate + GTP (ATP) + CoA

Krebs Step 6

Enzyme: succinate dehydrogenase. What happens: succinate is OXIDIZED, FAD is REDUCED to FADH2. REACTION: Succinate + FAD to fumarate + FADH2

Krebs Step 7

Enzyme: fumarase. What happens: water is ADDED. REACTION: Fumarate + H2O to malate

Krebs Step 8

Enzyme: malate dehydrogenase. What happens: malate is OXIDIZED, NAD+ is REDUCED to NADH; oxaloacetate is remade to restart the cycle. REACTION: Malate + NAD+ to oxaloacetate + NADH + H+

Krebs: overall reaction (1 turn)

Acetyl-CoA + 3 NAD+ + FAD + ADP + Pi + 2 H2O to 2 CO2 + 3 NADH + FADH2 + ATP + 3 H+ + CoA (2 turns per glucose)

Krebs: net final products

Per glucose (2 turns): 6 NADH + 2 FADH2 + 2 ATP + 4 CO2

Krebs: net ATP yield

2 ATP made directly per glucose (1 per turn). The NADH and FADH2 give 18 more in the ETC (15 + 3)

ETC Step 1

Complex I (NADH dehydrogenase). What happens: NADH is OXIDIZED to NAD+; its 2 electrons go to CoQ (CoQ REDUCED); 4 H+ PUMPED into the intermembrane space. REACTION: NADH to NAD+ + H+ + 2e-

ETC Step 2

Complex II (succinate dehydrogenase). What happens: FADH2 is OXIDIZED to FAD; its electrons go to CoQ; 0 H+ pumped (why FADH2 makes less ATP). REACTION: FADH2 to FAD + 2H+ + 2e-

ETC Step 3

CoQ (coenzyme Q, ubiquinone). What happens: mobile carrier that picks up electrons from Complexes I and II and carries them to Complex III

ETC Step 4

Complex III (cytochrome c oxidoreductase). What happens: CoQ is OXIDIZED; electrons go to cyt c (cyt c REDUCED); 4 H+ PUMPED

ETC Step 5

Cyt c (cytochrome c). What happens: small mobile carrier that brings electrons one at a time from Complex III to Complex IV

ETC Step 6

Complex IV (cytochrome c oxidase). What happens: cyt c is OXIDIZED; electrons go to O2, the final electron acceptor; O2 is REDUCED to water; 2 H+ PUMPED. REACTION: 1/2 O2 + 2 H+ + 2e- to H2O

ETC Step 7

ATP synthase. What happens: CHEMIOSMOSIS, H+ flows back into the matrix through ATP synthase, spinning it; OXIDATIVE PHOSPHORYLATION makes ATP. REACTION: ADP + Pi to ATP

ETC: net final products

Water (H2O) + NAD+ and FAD (recycled back to glycolysis and Krebs) + ATP

ETC: net ATP yield

About 28 ATP per glucose (10 NADH x 2.5 = 25, + 2 FADH2 x 1.5 = 3)

Lactic Acid Fermentation Step 1

Glycolysis. What happens: glucose is split into 2 pyruvate, making 2 ATP (substrate-level phosphorylation) and 2 NADH. REACTION: Glucose + 2 NAD+ + 2 ADP + 2 Pi to 2 pyruvate + 2 NADH + 2 ATP

Lactic Acid Fermentation Step 2

Enzyme: LDH (lactate dehydrogenase). What happens: pyruvate is REDUCED to lactate; NADH is OXIDIZED back to NAD+ so glycolysis can keep going; no CO2 released. REACTION: 2 pyruvate + 2 NADH to 2 lactate + 2 NAD+

Lactic Acid Fermentation: net final products

2 lactate + 2 ATP (NAD+ is recycled). Overall: Glucose + 2 ADP + 2 Pi to 2 lactate + 2 ATP

Lactic Acid Fermentation: net ATP yield

2 ATP per glucose (all from glycolysis)

Alcoholic Fermentation Step 1

Glycolysis. What happens: glucose is split into 2 pyruvate, making 2 ATP (substrate-level phosphorylation) and 2 NADH. REACTION: Glucose + 2 NAD+ + 2 ADP + 2 Pi to 2 pyruvate + 2 NADH + 2 ATP

Alcoholic Fermentation Step 2

Enzyme: pyruvate decarboxylase. What happens: CO2 is RELEASED from pyruvate, making acetaldehyde. REACTION: 2 pyruvate to 2 acetaldehyde + 2 CO2

Alcoholic Fermentation Step 3

Enzyme: alcohol dehydrogenase. What happens: acetaldehyde is REDUCED to ethanol; NADH is OXIDIZED back to NAD+ so glycolysis can keep going. REACTION: 2 acetaldehyde + 2 NADH to 2 ethanol + 2 NAD+

Alcoholic Fermentation: net final products

2 ethanol + 2 CO2 + 2 ATP (NAD+ is recycled). Overall: Glucose + 2 ADP + 2 Pi to 2 ethanol + 2 CO2 + 2 ATP

Alcoholic Fermentation: net ATP yield

2 ATP per glucose (all from glycolysis