Download MITOCHONDRIA

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
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 acetylcoA 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 + 2FADH + 4CO + 2
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 glycolysis
 2 NADH from pyruvate oxidation
 6 NADH from the Kreb’s Cycle and
 2 FADH2 from the Kreb’s Cycle
Most of the energy from glucose will be produced
in the next stage (ETC)