Cellular Respiration Oxidation of Pyruvate Krebs Cycle AP

Cellular Respiration Oxidation of Pyruvate Krebs Cycle AP Biology Modified from Kim Foglia 2006 -2007

Glycolysis is only the start § Glycolysis glucose pyruvate 6 C 2 x 3 C § Pyruvate has more energy to yield u u u 3 more C to strip off (to oxidize) if O 2 is available, pyruvate enters mitochondria enzymes of Krebs cycle complete oxidation of sugar to CO 2 pyruvate CO 2 AP Biology 3 C 1 C

Cellular respiration AP Biology

Oxidation of pyruvate § Pyruvate enters mitochondria [ 2 x pyruvate acetyl Co. A + CO 2 3 C 2 C 1 C NADH 3 step oxidation process u releases 1 CO 2 (count the carbons!) u reduces NADH (stores energy) u produces acetyl Co. A Acetyl Co. A enters Krebs cycle u where does CO 2 go? u § NAD AP Biology ]

Pyruvate oxidized to Acetyl Co. A reduction oxidation Yield = 2 C sugar + CO 2 + NADH AP Biology

Krebs cycle 1937 | 1953 § aka Citric Acid Cycle in mitochondrial matrix u 8 step pathway u Hans Krebs 1900 -1981 § each catalyzed by specific enzyme § step-wise catabolism of 6 C citrate molecule § Evolved later than glycolysis u AP Biology does that make evolutionary sense? § bacteria 3. 5 billion years ago (glycolysis) § free O 2 2. 7 billion years ago (photosynthesis) § eukaryotes 1. 5 billion years ago (aerobic respiration = organelles mitochondria)

Count the carbons! pyruvate 3 C 2 C 6 C 4 C This happens twice for each glucose molecule AP Biology acetyl Co. A citrate x 2 4 C 6 C oxidation of sugars CO 2 5 C 4 C 4 C 4 C CO 2

Count the electron carriers! pyruvate 3 C FADH 2 AP Biology 6 C 4 C NADH This happens twice for each glucose molecule 2 C citrate x 2 4 C 4 C acetyl Co. A ATP NADH 6 C reduction of electron carriers 4 C CO 2 NADH 5 C CO 2 NADH

Whassup? So we fully oxidized glucose C 6 H 12 O 6 CO 2 & ended up with 4 ATP! AP Biology

Electron Carriers = Hydrogen Carriers H+ § Krebs cycle produces large quantities of electron carriers NADH u FADH 2 u go to Electron Transport Chain u AP Biology H+ H+ H+ H+ ADP + Pi ATP H+

Energy accounting of Krebs cycle 4 NAD + 1 FAD 4 NADH + 1 FADH 2 2 x pyruvate CO 2 3 x 1 C 3 C 1 ADP 1 ATP Net gain = 2 ATP = 8 NADH + 2 FADH 2 AP Biology

So why the Krebs cycle? § If the yield is only 2 ATP, then why? u value of NADH & FADH 2 § electron carriers & H carriers w reduced molecules move electrons w reduced molecules move H+ ions § to be used in the Electron Transport Chain like $$ in the bank AP Biology

What’s the point? ATP The Point is to Make ATP! AP Biology 2006 -2007

And how do we do that? § Set up a H+ § H+ H+ gradient Allow the H+ to flow through ATP synthase ADP + Pi ATP ADP + Pi ATP Have we done that yet? AP Biology H+