Figure 4.

Genetic and bioenergetic models of health and disease. Life requires the flow of both information and energy. Disease and death result from dysfunction of either of these processes. (a) The organization, maintenance and expression of the information encoded in DNA is critical to surival. Information flows from DNA to RNA to proteins. DNA is moulded by mutation, recombination and natural selection. Genetic diseases are caused by specific defects in the nuclear genome that result in impaired or absent protein function. Disease can be directly attributed to the abnormal gene/protein. These defects tend to present early in life, be severe and are strongly selected against. They are therefore rare. (b) Life requires energy. The figure shows the flow of energy as the fall of electrons from a higher to a lower energy state. High-energy electrons are derived from organic food and the final electron acceptor is oxygen. The coupled assembly of ATP from ADP and organic phosphate is supported by the shift from a high-energy electron to a low-level state. The cell uses ATP to do work. The bioenergetic model of diseases is based on the concept that the bioenergetic machinery is vulnerable to thermodynamic entropy and somatic mutation. Selection to maintain bioenergetic systems in the post-reproductive years is weak. The age-related decline in bioenergetics makes cells vulnerable to various forms of stress, but additonal forces are needed for pathological ageing to occur. (Online version in colour.)