Cellular Respiration in the Mitochondria  Eukaryotes use mitochondria to produce the majority of the cell's ATP.  The cellular respiration reactions that occur in the mitochondria are: Pyruvate Oxidation (Link reaction), Krebs Cycle and the Electron Transport Chain (ETC)  They require oxygen and are considered aerobic.  Prokaryotes do these reactions in the cytoplasm with much less energy being produced.

Mitochondria  Oval shaped organelles with a double-membrane; randomly scattered around the cytoplasm.  The folded inner membrane is known as cristae. Many proteins and other molecules are embedded in it to help with the process of cellular respiration.  The matrix is the protein rich fluid inside the cristae.  The fluid-filled space between the two membranes is known as the intermembrane(-ous) space.

Pyruvate Oxidation (Link Reaction)  The two pyruvates formed at the end of glycolysis are transported into the matrix  In the matrix three changes occur, under the control of a multi-enzyme. 1. The carboxyl end is removed as carbon dioxide. This is known as a decarboxylation reaction and is catalyzed by pyruvate decarboxylase.

Pyruvate Oxidation continued… 2. Pyruvate becomes oxidized into acetate and NAD + is reduced to NADH + H + 3. A sulfur-containing compound (coenzyme-A) is attached to the acetate, forming acetyl-coA. (Co-A comes from vitamin B 5 (pantothenic acid)).

Products of Pyruvate Oxidation  The overall reaction: 2 pyruvate + 2NAD CoA --> 2 acetyl-CoA + 2NADH + 2H + + 2CO 2 The Acetyl-coA molecules enter the Kreb cycle, NADH go to the Electron transport chain to produce ATP. Carbon dioxide diffuses out of the cell as a waste product The protons (2H + ) stay in the matrix.

Acetyl-CoA  Acetyl-coA is the central molecule in energy metabolism.  The majority of macromolecules that catabolyze are changed into acetyl-coA.  Acetyl-coA can produce ATP or lipids.  If you need energy acetyl-coA enters the Krebs Cycle to go on to produce ATP.  If you do not need energy then acetyl- coA is used to produce fat for energy storage.

Kreb’s Cycle  Founded by Hans Krebs (biochemist at the Univ. of Sheffield) in  He won the Nobel Prize in 1953 along with Fritz Albert Lipmann who discovered the importance of coenzyme-A.  An 8-step process with each step catalyzed by a specific enzyme.  It is a cycle because the product of step 8 is the reactant in step 1 (oxaloacetate).

Kreb’s Cycle  The overall chemical equation is: 2 oxaloacetate + 2acetyl-coA + 2ADP + 2P + 6NAD + + 2FAD  2CoA + 2ATP + 6NADH + 6H + + 2FADH 2 + 4CO oxaloacetate  By the end of Pyruvate Oxidation and the Krebs Cycle, the original glucose molecule is consumed. The six carbon atoms have left as carbon dioxide molecules.

What’s left of Glucose?  All that is preserved are 4 ATP (two from glycolysis and two from the Krebs Cycle) and 12 reduced coenzymes/electron carriers: 2 NADH from glycolysis 2 NADH from pyruvate oxidation 6 NADH from the Kreb’s Cycle and 2 FADH 2 from the Kreb’s Cycle  Most of the energy from glucose will be produced in the next stage (ETC)