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CELLULAR RESPIRATION Overall Process C6H12O6 + 6O2 6CO2 + 6H2O + 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 – adenosine triphosphate 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 ATP Transport Work: ATP Phosphorylates Transport Proteins Mechanical Work: ATP Phosphorylates Motor Proteins ADP + P Chemical Work: ATP Phosphorylates Key Reactants Phosphate groups are removed and recycled as work is performed 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 pyruvate change makes 2 ATPs via substrate level phosphorylation and 1 NADH via redox 2. Krebs Cycle (aka citric acid cycle) • Occurs in presence of O2 • Occurs in inner space or matrix of mitochondria • Complete oxidation of glucose to CO2 occurs here 1. Pyruvate is oxidized into Acetyl CoA reducing NAD+ into NADH on the way • CO2 is formed 2. Acetyl CoA + oxaloacetic acid → citric acid 3. Citric acid is oxidized forming 2 CO2 as waste • This becomes oxaloacetic acid again @ end of cycle • This oxidation powers the reduction of 3 NAD+ 3 NADH and 1 FAD+ FADH2 as 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… 1. Photophosphorylation – plants use energy from sun to drive phosphorylation of ADP ATP 2. Substrate-level phosphorylation – glycolysis and Krebs cycle use proteins (substrates) to phosphorylate ADP ATP 3. 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