Biology Times (^) March 19
Proton Motive Force and ATP Synthesis
As in chloroplast, electron transfer is coupled to ATP synthesis by proton(H+) transport. The protons are
transferred from the matrix space into the intermembrane space by Complex I, Complex III and Complex
IV i.e., three of the four complexes. This creates a proton motive force (PMF). When the protons flow back
into the matrix through the channels of F 0 F 1 complexes (ATP synthases). ATP is synthesised from ADP and
Pi. Hence the mechanism of ATP synthesis during oxidative phosphorylation is by chemiosmosis. Each
NADH has enough energy to synthesise
3 ATP and each FADH 2 has enough energy to synthesise 2ATP.
The Respiratory Balance Sheet
The respiratory balance sheet gives theoretical value about net gain of ATP for every glucose molecule
oxidised. The calculations for respiratory balance sheet are based on some assumptions which are as
follows:- There is a sequential and orderly pathway in which one substrate makes the next substrate. Glycolysis,
TCA cycle and ETS pathway follow one after another. - NADH(+H+) is synthesised in glycolysis and is transferred into the mitochondria. The NADH(+H+)
undergoes oxidative phosphorylation within the mitochondria. - None of the intermediates in the pathway are utilised to synthesise any other compound.
- Glucose is the only substrate undergoing respiration. No other alternative substrates are entering in the
pathway at any stage.
But these assumptions may not be valid in a living system because all pathways work simultaneously.
There can be a net gain of 36 ATP or 38 ATP molecules during aerobic respiration of one molecule of
glucose.