2.2 - CELLULAR RESPIRATION: THE DETAILS 3 GOALS : BREAK 6 C-BONDS IN GLUCOSE (TO FORM CO 2 )

1. 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)

2. 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)

3. CELLULAR RESPIRATION: THE DETAILS • STAGE 1: GLYCOLYSIS • COLLECTIVELY MAKE UP THE FIRST TEN STEPS IN CELLULAR RESPIRATION • anaerobic, occurs in cell cytoplasm, mediated by enzymes • only energy-releasing process available to many prokaryotes (lacking mitochondria) • one 6-C glucose molecule two 3-C pyruvate (pyruvic acid) molecules (See Figure 11, P. 98 for explanations of short-forms) • 2 ATP molecules are used in steps 1 and 3 to “prime” the glucose molecule for cleavage in steps 4 and 5 and an energy return in steps 6-10

4. F1, 6-BP is split into DHAP and G3P DHAP is catalysed by isomerase into G3P

5.  both G3P molecules are processed the same way:  each G3P converted to BPG by adding phosphate group each H-atom released is used to reduce NAD+ to NADH (NADH + H+)  each BPG is converted to 3PG phosphate group from BPG (substrate-level) phoshorylatesADP to ATP each 3PG is rearranged to 2PG

6.  2PG converted to PEP (by removal of H2O) pyruvate (phosphate groups from pyruvate (substrate-level) phosphorylatesADP to ATP)

7. Summary Equation for Glycolysis • C6H12O6 + 2 ADP + 2 PI + 2 NAD+ 2 pyruvate + 2 ATP* + 2 NADP • (* net ATP yield = 4 ATP produced – 2 ATP used) • Energy Conversion Efficiency • = 2 x 30.5 kJ/mol ATP = 61 kJ = 2870 kJ • (2.1%) • but does not consider further processing of pyruvate and NADP in aerobic respiration in the mitochondria of eukaryotic organisms: • 2 membranes: • outer membrane serves as a cell membrane • inner membrane is folded into cristae, in/on which are imbedded or attached enzymes and other substances that participate in respiration reactions • 2 fluids: • a protein-rich liquid (matrix) occupies the innermost space of mitochondria • fluid-filled intermembrane space lies between inner and outer membrane • Reading - Stage 2: Pyruvate Oxidation + Stage 3: The Krebs Cycle