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Chemiosmosis and Oxidative
ATP Synthesis
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Chemiosmosis
Chemiosmosis: a process for synthesizing ATPusing the energy of
an electrochemical gradientand the ATP synthase enzyme
In simpler terms: The energy that drives thesynthesis of ATP
comes from the osmosis ofprotons through a membrane from
onecompartment into another
Although it is a misnomer according to todaysdefinition of
osmosis, the term chemiosmosiscontinues to be used to describe the
process
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Chemiosmosis
An electrochemical gradient is created inthe intermembrane space
of themitochondrion by the accumulation of
protons There are 2 components to the gradient:
1. Electrical- caused by a higher positivecharge in the
intermembrane space than inthe matrix
2. Chemical- caused by a higher concentrationof protons in the
intermembrane space thanthe matrix
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Electrochemical Gradient
The intermembrane space becomes an H+
reservoir because the inner mitochondrial
membrane is virtually impermeable to
protons
The electrochemical gradient creates a
potential difference or voltage across the
inner mitochondrial membrane
This is similar to the voltage in battery
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Chemiosmosis
The energy stored in the electrochemical
gradient produces a proton-motive force
This force moves protons through a proton
channel into the matrix An enzyme is associated with the
protein
channel called ATP synthase
The energy that is lost by the electrochemicalgradient is
harvested into the energy needed to
create a molecule of ATP
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ATP movement
Once formed by chemiosmosis, the newly
formed ATP molecules are transported
through the inner and outer mitochondrialmembranes by
facilitated diffusion into the
cytoplasm
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Cellular Respiration
The continual production of ATP by this
method is dependent on the establishment
and maintenance of an H+ reservoir
This condition requires the continual
movement of electrons through the ETC,
which is dependent on the availability of
oxygen for the Krebs Cycle as a finalelectron acceptor
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Without food (glucose) there would be no
electrons in the first place
All of the phases of cellular respiration are
therefore linked to each other
Cellular Respiration
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Recap!
1. Glycolysis
- 2 NADH
2. Formation of Acetyl CoA
- 2 NADH
3. Krebs Cycle
- 6 NADH
- 2 FADH2
Total:
2 FADH2 4 ATP
6 ATP
18 ATP
4 ATP
3 ATP each
2 ATP each
2 ATP each
3 ATP each
32 ATP
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