MitochondriaStructure: 2 membranes separated by a fluid filled space Inner membrane is folded to form cristae – provides large surface area for the attachment of enzymes involved in respiration. Central part is the matrix. Contains protein, traces of DNA and lipids. DNA allows mitochondria to produce its own proteins. Enzymes found in the matrix.Intermembrane space has protons (H+) pumped into it Lots of mitochondria are found in active cells (like muscle) which require plentiful supply of ATP.

Function Site where ATP is produced during respiration

Chemiosmosis and ATP production

Osmosis is the passive flow of water molecules down a concentration gradient through a partially permeable membrane.

Chemiosmosis is similar but instead of water moving, it is protons that pass down a concentration gradient.

The net production of ATP from one molecule of glucose is, in theory, 36.

Biochemists have discovered that the actual production is closer to 30 ATP’s and propose that this discrepancy occurs because some protons are used to transfer ATP from the matrix to the cytoplasm.

There are also losses such as the cost of moving pyruvate, phosphate and ADP (for ATP synthesis) into the mitochondria.

Nature of Science – Paradigm shift – chemiosmosis theory required a

significant change of view

The chemiosmosis hypothesis was proposed in 1961 by Peter Mitchell (1920-1992) to explain how the mitochondria convert ADP to ATP.

At the start of the 1960’s, scientists did not understand the exact mechanisms by which electron transfer is coupled to ATP synthesis.

Various hypotheses current at the time proposed a direct chemical relationship between oxidising and phosphorylating enzymes and proposed that a high-energy intermediate compound was formed.

Nature of Science – Paradigm shift – chemiosmosis theory required a

significant change of view

Mitchell’s theory was completely new and proposed an indirect interaction between these enzymes with no intermediate compound.

He suggested that ATP synthesis is driven by a reverse flow of protons down a concentration gradient, the so-called ‘chemiosmotic theory’.

This theory was first received with scepticism as his work was considered to be radical and outside the popularly held view.

Nature of Science – Paradigm shift – chemiosmosis theory required a

significant change of view

Mitchell struggled to persuade his contemporaries to reject the more accepted theories because his theory used a completely different approach.

After several years of research, he published detailed evidence to support his theory, both in a pamphlet in 1966 and further books.

Eventually in the early 1970’s, Mitchell’s chemiosmosis theory gained scientific acceptance, and scientists conceded that no high-energy intermediate compounds were likely to be found.

Mitchell was awarded the Nobel prize for chemistry in 1978.