Aerobic respiration occurs within cells.
It starts with glycolysis in the cytosol of the cell.
It then goes through the link reaction moving into the matrix of the mitochondria.
It then goes through the citric acid cycle within the mitochondria matrix.
Then it goes through the electron transport chain and chemiosmosis in the inner mitochondrial
membrane producing energy in the form of ATP.
In this video we are going to look at the fifth and final process involved in Aerobic
Respiration, Chemiosmosis.
Chemiosmosis occurs in the inner mitochondrial membrane, and is coupled with the electron
transport chain.
It occurs through an additional membrane protein called ATP synthase, which as the name suggests
is involved in the production of ATP.
ATP synthase is a rotating molecular motor consisting of a F0 subunit, which consists
of the rotating rotor that sits in the inner mitochondrial membranes, and the Stator which
is anchored in the inner mitochondrial membrane.
ATP Synthase also has a F1 subunit composed of the internal rod that also rotates, and
the catalytic nobs.
At the end of the electron transport chain we were left with a hydrogen concentration
gradient, with a higher gradient in the intermembrane space compared to the mitochondria matrix.
The hydrogen (H+) protons that are in a higher concentration in the intermembrane space want
to move down their concentration gradient into the lower concentrated area of the matrix.
These hydrogen (H+) protons moves through a channel in the stator of ATP Synthase.
Once they exit the channel they bind to binding sites on the rotor, this binding causes a
change in the shape of the rotor subunit which in turn causes the rotor to rotate within
the membrane.
Once the hydrogen (H+) makes a complete rotation, it moves through a second channel in the stator
that leads into the matrix.
The Catatylic nob consist of several subunits, including 3 catalytic subunits, that can be
found in three different states.
ADP and Phosphate (P) binding state, ATP forming state and ATP releasing state.
The movement of the rotor also causes the internal rod to rotate which causes these
catalytic sites in the knob to activate.
The movement of the internal rod causes the shape of the subunit to change and forces
ADP and Phosphate (P) already bound in an active site to join to create a new ATP molecule
that is bound in the active site.
As the internal rod continues to rotate and change the structure of the knobs subunits,
the ATP is released and is able to bind more ADP and Phosphate (P).
Oxidative Phosphorylation is the process that occurs on the inner mitochondrial membrane
to produce energy in the form of ATP.
It involves both the process of The Electron Transport Chain in the oxidisation of NADH
and FADH2 to produce a proton concentration gradient and also Chemiosmosis where the ATP
Synthase is powered by this gradient to form ATP.
Now that we have ATP being produced, what we really want to known is how much ATP is
produced in aerobic respiration for each molecule of Glucose that initially enters Glycolysis.
During aerobic respiration we get 2 ATP directly from glycolysis, 2 from the citric acid cycle.
This gives us 4 ATP and a total of 10 NADH and 2 FADH2’s that go into the electron
transport chain.
For each NADH that goes into the electron transport chain passing on its 2 e-, 4 H+
are pumped in complex I, 4 H+ in complex III and 2+ in complex IV giving a total of 10
H+ protons pumped for each NADH molecule.
For each FADH2 that goes into the electron transport chain passing on its 2 e-, 4 H+
are pumped through at complex III and 2 H+ at complex IV giving a total of 6 H+ pumped
for each FADH2 molecule.
But how many ATP are produced for each NADH and FADH2?
This number varies and relates to the number of subunits on the rotor.
In each rotation of the rotor on the ATP Synthase, 3 ATP are made in the catalytic knob.
The amount of hydrogen (H+) needed to produce a molecule of ATP depends on the number of
subunits on the F0 rotor, this number varies depending on the species the ATP synthase
is found in, but usually somewhere between 8 and 15.
If it has 9 subunits, it will take 9 H+ to rotate once and produce 3 ATP, which equates
to 3 H+ to make a single ATP.
A hydrogen proton (H+) is also used in the ATP-ADP translocase to get the ATP out of
the matrix, raising this number to 4 H+ per ATP molecule.
In this scenario, for every NADH with 10 H+ protons pumped, its 2.5 ATP, and for every
FADH2 with 6 H+ pumped its 1.5 ATP.
So for 10 molecules of NADH you would get 25 ATP, and 2 molecules of FADH2 would give
you 3 ATP, plus the 2 produced in glycolysis and 2 in citric acid cycle, you would get
a total of 32 ATP per molecule of glucose.
Many calculations round up the estimate of ATP to 3 ATP for each NADH and 2 ATP for each
FADH2, which would give a total of 30 ATP from NADH, 4 from FADH2 plus the 2 from glycolysis
and 2 from citric acid cycle, giving a total of 38 ATP for each molecule of glucose.
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