OVERVIEW 10 reactions Convert glucose (6C) to 2 pyruvate (3C) Produces: 4 ATP & 2 NADH Consumes: 2 ATP Net yield: 2 ATP & 2 NADH glucose C-C-C-C-C-C fructose-1,6bP P-C-C-C-C-C-C-P DHAP P-C-C-C G3P C-C-C-P pyruvate C-C-C ATP 2 ADP 2 4 NAD + 2 2Pi2Pi 2Pi2Pi 2H2H 2 DHAP = dihydroxyacetone phosphate G3P = glyceraldehyde-3-phosphate 4 ATP

CELLULAR RESPIRATION Stage 2 & 3: Oxidation of Pyruvate Krebs Cycle Also called Link Reaction

GLYCOLYSIS IS ONLY THE START Glycolysis Pyruvate has more energy to yield 3 more C to strip off (oxidize) If O 2 is available, pyruvate enters mitochondria Enzymes of Krebs cycle complete the full oxidation of sugar to CO 2 glucose      pyruvate 2x2x 6C3C pyruvate       CO 2 3C 1C

CELLULAR RESPIRATION

MITOCHONDRIA - STRUCTURE Double membrane, energy-harvesting organelle Smooth outer membrane Highly folded inner membrane Cristae Intermembrane space Fluid-filled space between membranes Matrix Inner fluid-filled space DNA, ribosomes Enzymes intermembrane space inner membrane outer membrane matrix cristae mitochondrial DNA What cells would have a lot of mitochondria?

MITOCHONDRIA - FUNCTION What does this tell us about the evolution of eukaryotes? Endosymbiosis! Dividing mitochondria Who else divides like that? Advantage of highly folded inner membrane? More surface area for membrane- bound enzymes & permeases Membrane-bound proteins Enzymes & permeases bacteria! Oooooh! Form fits function!

MITOCHONDRIA - STRUCTURE Pyruvate enters mitochondrial matrix 3 step oxidation process Releases 2 CO 2 Reduces 2 NAD  2NADH Produces 2 acetyl-CoA Acetyl-CoA enters Krebs cycle pyruvate    acetyl CoA + CO 2 NAD 3C2C 1C [ 2x ] Where does the CO 2 go? Exhale!

PYRUVATE OXIDIZED TO ACETYL-COA Yield = 2C sugar + NADH + CO 2 reduction oxidation Coenzyme A Pyruvate Acetyl CoA C-C-C C-C CO 2 NAD + 2 x []

KREBS CYCLE aka Citric Acid Cycle In mitochondrial matrix 8 step pathway Each catalyzed by specific enzyme Step-wise catabolism of 6C citrate molecule Evolved later than glycolysis Does that make evolutionary sense? Bacteria  3.5 bya (glycolysis) Free O2  2.7 bya (photosynthesis) Eukaryotes  1.5 bya (aerobic prokaryote  mitochondria = organelle) Hans Krebs

COUNT THE CARBONS 4C 6C 4C 2C6C5C4C CO 2 citrate acetyl CoA 3C pyruvate x2x2 oxidation of sugars This happens twice for each glucose molecule

COUNT THE ELECTRON CARRIERS 4C6C4C 2C6C5C4C CO 2 citrate acetyl CoA 3C pyruvate reduction of electron carriers This happens twice for each glucose molecule x2x2 NADH FADH 2 ATP

WHAT’S HAPPENED SO FAR? We have fully oxidized glucose …C 6 H 12 O 6 ...… CO 2 & ended up with 4 ATP What’s the point?

ELECTRON CARRIERS = HYDROGEN CARRIERS Krebs cycle produces large quantities of electron carriers NADH FADH 2 Go to Electron Transport Chain What’s so important about electron carriers? H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ATP ADP + P i

ENERGY ACCOUNTING OF KREBS CYCLE Net gain=2 ATP =8 NADH + 2 FADH 2 1 ADP1 ATP ATP 2x 4 NAD + 1 FAD4 NADH + 1 FADH 2 pyruvate          CO 2 3C 3x3x 1C

VALUE OF KREBS CYCLE If the yield is only 2 ATP, then how was the Krebs cycle a successful adaptation? The value is in NADH & FADH 2 Electron carriers & H carriers Reduced molecules move electrons Reduced molecules move H + ions To be used in the Electron Transport Chain like $$ in the bank

What’s the point? The point is to make ATP ! ATP

AND HOW DO WE DO THAT? ATP Synthase Set up a H + gradient Allow H + to flow through ATP synthase Conformational change bonds P i to ADP ADP + P i  ATP H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ATP ADP P + But… How do we get here?

We’re not done yet! Any questions so far?