Download Aerobic Respiration

Aerobic Respiration
In summary, aerobic respiration is:
• Glycolysis – the phosphorylation of glucose to 6C
hexose phosphate, then splitting into 2 x 3C
triose phosphate molecules which are oxidised to
form 2 x pyruvate, yielding a little ATP and
reduced NAD. In cytoplasm.
• Link reaction - pyruvate is decarboxylated and
hydrogenated. The remaining 2C unit is added to
CoA to form AcetylCoA. This occurs twice for
every glucose molecule as 2 x pyruvate are
formed. In mitochondria.
Acetyl Coenzyme A
• A complex organic molecule containing a
nucleotide (adenine and ribose) with a B
group vitamin (pantothenic acid)
• Acts as a carrier of acetyl groups to the Kreb’s
cycle
• Acetyl CoA (2C) then combines with
oxaloacetate (4C)to form citrate (6C) which
then enters the Kreb’s cycle in mitochondria.
• During the Kreb’s cycle, citrate is reconverted
to oxaloacetate in a series of small steps.
• These processes involve decarboxylation and
dehydrogenation, using NAD and FAD as
hydrogen carriers.
• For each turn of the cycle 2 CO2 molecules are
produced, one FAD and 3 NAD are reduced,
and one ATP generated.
• Finally, oxidative phosphorylation occurs,
converting ADP to ATP using energy from the
activity of electrons in the electron transfer
chain (ETC). Also in mitochondria.
• Reduced NAD and FAD are passed to the ETC
where hydrogen is removed and split into H+
and an electron.
• The electron is transferred to the first electron
carrier, whilst H+ remains in solution.
• As the electron is transferred to oxygen, H+ is
drawn from solution to reduce oxygen to
water.
• The transfer of electrons makes energy
available to convert ADP + Pi to ATP.
• As an electron passes from a carrier at a
higher level to one at a lower level, energy is
released.
• This energy is usually lost as heat but at
particular points in the ETC it is enough to
produce ATP.
• 3xATP produced for each reduced NAD.
• 2xATP produced for each reduced FAD.
Balance Sheet of ATP
Glycolysis
Link reaction
Kreb’s cycle
Oxidative
phosphorylation
TOTAL
ATP used ATP made Net ATP
2
4
+2
2
+2
-2
34
40
+34
+38
Glycolysis
Anaerobic
pathways
Link
reac
tion
Kreb’s Cycle
Oxidative
phosphory
lation
Chemiosmosis
Chemiosmosis is the most likely explaination for the
synthesis of ATP in oxidative phosphorylation.
Energy released by ETC is used to pump hydrogen ions into
the space between the two membranes of the
mitochondrial envelope.
Concentration of H+ in intermembrane space >
concentration of H+ in mitochondrial matrix.
H+ ions pass back into mitochondrial matrix through
protein channels in inner membrane.
ATP synthetase associated with channels.
As H+ passes through, their electrical potential energy is
used to synthesise ATP from ADP +Pi.