4. Thermodynamics of Bioreactions

Each electron transferred from the electron donor to the electron acceptor liberates an energy quantum of 1.602 10⁻¹⁹ J per V potential difference. Hence for 1 mol transferred, the liberated energy is 6.023×10²³ × 1.602×10⁻¹⁹ = 96,490 J/V. This explains (3), as well as the value of Faradays constant.

Peter D Mitchell (1920–1992) is one of the few “modern” bioscientists who has made his most important discoveries outside of the “teams” that now seem to dominate the field. After an early health-related retirement in 1963 from a readership at Edinburgh he formed a small and more or less privately funded research team with his associate Jennifer Moyle at an old estate in Cornwall that he restored himself. The purpose of the “Glynn foundation” was to promote fundamental biochemical research, and the many important papers from his hand that were rewarded with the Nobel prize in 1978 prove that meaningful research can also be conducted by small teams.

Many of these experiments are commented in Nath (2010) and in the references cited therein.

The enzyme F ₀ − F ₁ ATP synthase consists of two parts, F _o, embedded in the inner mitochondrial membrane, and F ₁ that protrudes like a ball on the matrix side of the membrane (as clearly seen on electro micrographs). F _o and the stalk that connects it with F ₁ channels the ions back to the mitochondrial matrix while ATP synthesis occurs by the concerted action of the many subunits of F ₁. An intuitively appealing description of how ions, in particular protons, from the intermembrane space flow back to the matrix is given by Oster et al. (2000). He finds that protons flow in a helical movement that makes the stem of the F _o rotate. The rotation of the stem “winds up” certain subunits of F ₁ as is done by the winch of a crossbow. When sufficient potential energy is accumulated the bolt of free energy (=ATP) is released to allow the three part-process of ATP synthesis to proceed: Binding of ADP and free phosphate, ATP synthesis, and finally removal of ATP from F ₁ into the mitochondrial matrix.