2.1 – CELLULAR RESPIRATION: THE BIG PICTURE

1. 2.1 – CELLULAR RESPIRATION: THE BIG PICTURE • What do we all need? • ENERGY! • Organisms have evolved adaptations that allow them to harness free energy, convert it, and use it to power the endergonic processes of life • autotrophs convert light energy into chemical potential energy by changing simple inorganic compounds (CO2, H2O) into glucose (C6H12O6) and other carbohydrates, which are then passed on to heterotrophs, including decomposers which recycle the CO2 and H2Oback to the producers

2. consumers use a series of endergonic enzyme-mediated redox reactions to break the covalent bonds in glucose and rearrange them into more stable configurations, resulting in a release of free energy • aerobic cellular respiration is a combustion reaction which transfers electrons from glucose to oxygen  C6H12O6 is oxidized to CO2 and O2 is reduced to H2O • Summary Equation: • C6H12O6(aq) + 6O2(g) 6CO2(g) + 6 H2O(l) + heat + ATP • (actually a series of 20 redox reactions, each step catalyzed by a specific enzyme) • C-H bonds in nutrients are oxidized in two ways: • C-H bonds are relatively non-polar (En=0.4)  12 H atoms break away from C6H12O6 and become attached to 6 O atoms from the 6 O2 molecules to become 6 H2O molecules • C6H12O6(aq) + 6O2(g) 6CO2(g) + 6 H2O(l) • (oxidation because H atoms carry e- away from C atoms in glucose to O atoms) • shared e- pairs occupy positions closer to the oxygen nuclei than in the glucose molecule • decrease in potential energy plus increased entropy releases free energy • The other half of the combustion process involves the attachment of the remaining O atoms to C atoms, forming the 6 CO2 on the product side of the equation CC6H12O6(aq) + 6O2(g) 6CO2(g) + 6 H2O(l) (also an oxidation because highlyelectronegative O atoms draw the shared e- pairs of the C atoms closer to themselves)

3. more stable configuration results in the release of free energy • overall, the aerobic oxidation of glucose involves the movement of valence electrons from a higher free energy state in glucose to a lower free energy state in carbon dioxide and water • G = 2870 kJ/mol C6H12O6 34% is trapped by moving electrons in certain molecules to higher free energy states (i.e. ATP) • activation energy prevents spontaneous combustion and allows for control of the oxidation process • O is not a strong enough oxidizer to strip electrons from the H-C bonds in glucose by itself •  specific enzymes catalyze every step, lowering the activation energy and allowing reactions to occur at a rate that meets the needs of the cell at a reasonable temperature • obligate anaerobes use NO2, SO4, CO2, and Fe3+ as final electron acceptors and many are pathogenic (i.e. Clostridium tetani, C. botulinum, and C. perfringens, responsible for gas gangrene) • facultative anaerobes include E. coli , Vibrio cholerae, and Salmonella enteritidus • Section 2.1 Review Questions – P. 93, #1-4 • Reading – 2.2 (Energy Transfer and Glycolysis, P. 94-100)

4. 2.2 - CELLULAR RESPIRATION: THE DETAILS • 3 GOALS: • BREAK 6 C-BONDS IN GLUCOSE (TO FORM CO2) • MOVE H-ATOM (e-) FROM GLUCOSE TO OXYGEN (TO FORM H2O) • (ULTIMATELY) TRAP RELEASED FREE ENERGY INTO ATP • occurs in four stages (glycolysis, pyruvate oxidation, Krebs cycle, and electron transport and chemiosmosis) and three locations (cytoplasm, matrix, and inner membrane of mitochondria) in the cell (Fig. 1, P. 94) • Energy Transfer • capture of free energy in the form of ATP is accomplished through two distinct energy-transfer mechanisms: • Substrate-Level Phosphorylation (forms 4 ATP molecules in glycolysis, 2 in the Krebs cycle, for every glucose molecule processed) • enzyme catalyzes direct transfer of phosphate group (and 50kJ/mol energy) as part of a phosphate-containing compound (i.e. PEP in glycolysis) to ADP, forming ATP (Fig. 2)

5. Oxidative Phosphorylation (forms 32 ATP molecules in all stages, for every glucose molecule processed) • indirect formation of ATP through a series of redox reactions with oxygen as the final electron acceptor (hence oxidative) • dehydrogenase catalyzes removal of 2 H-atoms (2 protons, 2 electrons) from glucose by coenzyme NAD+, reducing it to NADH (shortened from NADH + H+, remaining proton dissolves into cytoplasm) • occurs in glycolysis, pyruvate oxidation, and 3 reactions of the Krebs cycle (Fig. 6, P. 96) • another coenzyme, FAD, is also reduced by 2 H-atoms from the original glucose molecule, forming FADH2 • occurs in one reaction in the Krebs cycle • reduced coenzymes NAD+ and FAD move free energy from place to place and molecule to molecule  transfer of free energy to ATP occurs in the electron transfer/chemiosmosis process and requires the use of free oxygen molecules •  Read Stage 1: Glycolysis (P. 97-100)