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CELLULAR RESPIRATION. Overall Process. C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + ENERGY Purpose: Organisms routinely break down complex molecules in controlled steps and use energy released (in the form of ATP) from this catabolic process to do work. ATP – a denosine t ri p hosphate.
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Overall Process C6H12O6 + 6O2 6CO2 + 6H2O + ENERGY Purpose: Organisms routinely break down complex molecules in controlled stepsand use energy released (in the form of ATP) from this catabolic process to do work.
Phosphate bonds • PO4 bonds are high energy bonds • Require energy to make • Release energy when broken
Phosphorylation • Adding a phosphate group to any molecule • Ex: ADP + Pi ATP • Oxidative phosphorylation – phosphorylation results from redox reactions • Substrate-level phosphorylation – phosphate group transfers from a molecule (“substrate”) instead of ADP + Pi ADP
How ATP Drives Cellular Work • Transport Work: • ATP Phosphorylates Transport Proteins • Mechanical Work: • ATP Phosphorylates Motor Proteins • Chemical Work: • ATP Phosphorylates Key Reactants • Phosphate groups are removed and recycled as work is performed ADP + P ATP
Cellular Respiration • Divided into 3 parts: • 1. Glycolysis • 2. Krebs Cycle (aka Citric Acid Cycle) or Fermentation • 3. Oxidative phosphorylation (ETC & Chemiosmosis)
1. Glycolysis • Breakdown of glucose into pyruvate in cytoplasm w/ or w/o presence of O2 • 2 phases: • Investment phase: use 2 ATP to break up glucose into 2 PGAL (C-C-C-p) • Payoff phase: each PGAL turns into pyruvate (C-C-C) • Each PGAL pyruvatechange makes 2 ATPs via substrate level phosphorylation and 1 NADH via redox
Occurs in presence of O2 Occurs in inner space or matrix of mitochondria Complete oxidation of glucose to CO2 occurs here 2. Krebs Cycle (aka citric acid cycle)
1. Pyruvate is oxidized into Acetyl CoA reducing NAD+ into NADH on the way • CO2 is formed • 2. Acetyl CoA + oxaloaceticacid → citric acid
3. Citric acid is oxidized forming 2 CO2 as waste • This becomes oxaloaceticacid again@ end of cycle • This oxidation powers the reduction of 3 NAD+ 3 NADHand 1 FAD+ FADH2as well as the phosphorylation of ADP ATP. • Also get e-’s and protons (H+) for ETC/Chemiosomosis
ETC • Occurs in the inner membrane of mitochondrial matrix • Energy released as e- travels down • ETC is used to establish a proton • gradient
Final electron acceptor is O2 • 2H+ (from FADH2 and NADH) • 2e- (from FADH2 and NADH) • ½ O2 • H2O!
Key Points • No ATP is generated during ETC; ATP comes from chemiosmosis! • Source of e- = NADH and FADH2 reduction • Source of H+ = same as above!
Phosphorylation… • Photophosphorylation– plants use energy from sun to drive phosphorylation of ADP ATP • Substrate-level phosphorylation – glycolysis and Krebs cycle use proteins (substrates) to phosphorylate ADP ATP • Oxidative phosphorylation – in ETC, redox reactions drive production of ATP • This is where most of ATP generated from cell respiration comes from!
Fermentation • Process whereby cells produce ATP without O2 • Alcohol fermentation – pyruvate is converted to ethanol • CO2 released • Lactic acid fermentation – pyruvate is reduced directly by NADH to form lactate • No CO2 released