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 B5 (pantothenic acid)).

Products of Pyruvate Oxidation

The overall reaction:2 pyruvate + 2NAD+ + 2 CoA -->

2 acetyl-CoA + 2NADH + 2H+ + 2CO2

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

productThe 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 1937.

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+ + 2FADH2 + 4CO

2 + 2

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 glycolysis2 NADH from pyruvate oxidation6 NADH from the Kreb’s Cycle and2 FADH2 from the Kreb’s Cycle

Most of the energy from glucose will be produced in the next stage (ETC)