Citric Acid Cycle: Complete oxidation of carbon molecules Chapter Pgs Objective: I can describe and count the overall number of reactants and products involved in the Krebs Cycle while being able to analyze a document with details of the process.

At the end of Glycolysis… Main product: 2 molecules of pyruvate Other products: 2 NADH (to carry electrons) 4 ATP + 2 ADP = 2 ATP net profit were made 2 H 2 O GLYCOLYSIS Glucose  2 ATP  2 NAD+  4 ADP   2 ADP  2 NADH  2H 2 O  2 pyruvate molecules  4 ATP What happens next?

In-between Major Stages “Transition Step” or “Linking Step” ▫ In between Glycolysis and Citric Acid Cycle (both order and location) Glycolysis occurs in the cytosol Transition step occurs in the mitochondria (intermembrane space) Citric Acid Cycle occurs in ▫ The mitochondria (matrix) How many pyruvate were made in glycolysis ( 1 glucose)? 2, so everything about to describe happens TWICE…

Transition Step: Oxidation of Pyruvate Pyruvate (made of 3 carbons) ▫ Is oxidized BEFORE entering C.A. Cycle ▫ NAD+ oxidizes it  Turns into NADH ▫ CO 2 is released ▫ Left w/ 2 carbons called acetate (unstable) ▫ Coenzyme A attaches to carry it: now called Acetyl-CoA (2 carbons) Krebs Cycle

Transition Step: Junction of other metabolic pathways Acetyl-CoA enters the C.A. Cycle (to make more ATP with rest of cellular respiration) ▫ If there’s enough ATP,  Acetyl-CoA turns to Fat ▫ Fat (and Protein) can be turned into Acetyl-CoA (when glucose unavailable) C.A. Cycle

Citric Acid Cycle – General Facts 2 nd Stage in Cellular Respiration Occurs in the mitochondria (matrix) Does not need oxygen (but oxidation still occurs) Main reactant: Acetyl-CoA (2 carbons) Main job: oxidize carbon compounds (harvest electrons to go to ETC) Main product: None – occurs in a cycle Other products: electron carriers (NADH, FADH 2 ) and ATP and CO 2 (by-product) AKA Krebs Cycle, Tricarboxylic acid cycle

Krebs Cycle – Detailed Facts (you need to know) 8 enzyme-catalyzed reactions in a cycle (8 steps) ▫ Won’t need to memorize all 8 steps  Will still expose you to all 8… ▫ Will break down to 4… 1) Acetyl Co-A joins the cycle: 2-carbon molecule bonds with 4-carbon molecule that’s already in cycle (oxaloacetate) (Co-A leaves to get another 2-carbon molecule) 6 carbon molecule formed (NOT glucose) Called citrate  name of cycle

Krebs Cycle – Detailed Facts (you need to know) 6-carbon molecule oxidized by NAD+ ▫ NADH is made ▫ CO 2 is released ▫ 5 carbons left 5-carbon molecule oxidized by NAD+ ▫ NADH is made ▫ CO 2 is released ▫ 4 carbons left ▫ ALSO, ATP is made 2) NAD+ ADP 3)

Krebs Cycle – Detailed Facts (you need to know) 4) 4-carbon molecule is oxidized TWICE NAD +  NADH FAD 2+  FADH 2 Atoms in 4-carbon molecule rearranged to turn molecule back into what started the cycle with Acetyl-CoA *Cycle starts again! NAD + FAD 2+

Krebs Cycle – Detailed Facts (you don’t need to know) Each product (substrate for next rxn) has a name Specific steps when each “side product” is made Each step run by a different enzyme (named!)

After Krebs Cycle… (summary) NADH and FADH 2 sent to ETC (oxidized by oxygen – lose electron; turn back to NAD+ and FAD 2+  return to Krebs Cycle) Little ATP made can be used by the cell How much was made (Transition + Krebs)? ▫ NADH = 4 x 2 = 8 ▫ FADH 2 = 1 x 2 = 2 ▫ ATP = 1 x 2 = 2 ▫ CO 2 = 3 x 2 = 6  by-product – to be exhaled 1 glucose makes 2 pyruvate, so will have 2 turns of Krebs (+ Transition)

The Story So Far… (summary) Start with 1 molecule of glucose In glycolysis will make… ▫ 2 NADH (carry e- = nrg) ▫ 2 ATP (net) = energy! ▫ 2 pyruvate molecule + 2H 2 O In Transition + Krebs Cycle will make (from 2 pyruvate) ▫ 8 NADH (carry e- = nrg) ▫ 2 FADH 2 (carry e- = nrg) ▫ 2 ATP = energy! ▫ 6 CO 2 = unneeded by product So, can add up what you have before oxidative phosphorylation in the ETC…

Cont Cut-Out Activity…BUT!!! Don’t worry about bonds Don’t worry about hydrogen (H) ▫ Show as Carbon molecules (assumed to have bonds/electrons/H in molecule) MAKE SURE THAT CYCLED MOLECULES CAN FLIP (write both sides) ▫ ATP ↔ ADPNAD+ ↔ NADH ▫ Need to have the correct # of molecules in the end Show ALL: Glycolysis + T.S. + Krebs