MITOCHONDRIA

1
MITOCHONDRIA

• Oval shaped organelles randomly scattered around
  the cytoplasm.
• Energy factories of the cell produce the
  majority of the cell's ATP
• These ATP producing reactions cannot take place
  without oxygen, therefore the steps of cellular
  respiration that occur in the mitochondria are
  said to be aerobic.
• Pyruvate Oxidation (Link reaction), Krebs Cycle
  and the Electron Transport Chain (ETC) are all
  aerobic.
• Eukaryotes use mitochondria to produce cellular
  energy. Prokaryotes do these reactions in the
  cytoplasm and with much less energy being
  produced.

2
MITOCHONDRIA

• The mitochondria are double-membraned organelles.
  
• The folded inner membrane is known as cristae.
  The cristae has many proteins and other molecules
  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.
• Mitochondria have their own DNA, mtDNA, and can
  therefore reproduce on their own. This mtDNA is
  very similar to prokaryotic DNA and has lead to
  the creation of the endosymbiosis hypothesis
  which states that mitochondria are descendants of
  early prokaryotic cells who developed a symbiotic
  relationship with early eukaryotic cells.

3
PYRUVATE OXIDATION (LINK REACTION)?

• The two pyruvates formed at the end of glycolysis
  are transported into the matrix
• In the matrix, under the control of a
  multi-enyzme, three changes occur.
• The carboxyl end is removed as carbon dioxide.
  This is known as a decarboxylation reaction and
  is catalyzed by pyruvate decarboxylase.
• Pyruvate becomes oxidized into acetate and NAD
  is reduced to NADH H
• A sulfur-containing compound (coenzyme-A) is
  attached to the acetate, forming acetyl-coA.

4
PYRUVATE OXIDATION

• Co-A comes from vitamin B5 (pantothenic acid).
• The overall reaction
• 2 pyruvate 2NAD 2 CoA --gt 2 acetyl-CoA
  2NADH 2H 2CO2
• Acetyl-coA enters the Kreb cycle,
• NADH go to the electron transport chain to
  produce ATP by oxidative phosphorylation
• Carbon dioxide diffuses out of the cell as a
  waste produt
• The protons (2H) stay in the matrix.
• Acetyl-coA is the central molecule in energy
  metabolism. The majority of macromolecules that
  we use for catabolism are changed into
  acetyl-coA.
• Acetyl-coA can produce ATP or lipids. If you
  need energy you get it as acetyl-coA enters the
  Krebs Cycle. If you do not need energy then
  acetyl-coA is used to produce fat for energy
  storage.

5
KREBS 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).

6
KREBS CYCLE

• The overall chemical equation is
• Oxaloacetate acetyl-coA ADP P 3NAD FAD
• --gt CoA ATP 3NADH 3H FADH2 2CO2
  oxaloacetate
• By the end of the Krebs Cycle, the original
  glucose molecule is consumed. The six carbon
  atoms have left as carbon dioxide molecules.
• All that is preserved are 4ATP (two from
  glycolysis and two from the Krebs Cycle) and 12
  reduced coenzymes
• 2 NADH from glycolysis
• 2 NADH from pyruvate oxidation
• 6 NADH from the Krebs Cycle and
• 2 FADH2 from the Krebs Cycle
• Most of the energy from glucose will be produced
  in the next stage (ETC)
• Notice in the figure on page 103 that all the
  carbons in the original glucose molecule are
  transformed into carbon dioxide.