Although the term redox covers an important number of chemical reactions, biochemists are more familiar with reactions involving the reactions mediated by electron transfer chains associated with respiration, the thiol-disulfide exchanges and the reactions occurring in the presence of free radicals. More recently, the importance of these reactions in the living world and in medicine has been recognized by biochemists, biologists, physiologists, physicians, etc. The importance of the subject in both fundamental and is reflected by the abundance of interesting reviews applied science concerning the subject (Cadenas, 1989, Del Maestro, 1991) and books (Dreosti, 1991; Rice-Evans and Burdon, 1994; Armstrong, 1994) The aim of this chapter is to describe basic reactions known with references to reviews covering special subjects related to redox reactions. Transformation of energy in living organisms is mediated by complex biological systems such as electron transfer chains where the succession of redox reactions provides energy to the organisms. Molecular oxygen or dioxygen is an essential molecule and is the terminal acceptor of electrons during respiration in eukaryotes. In these organisms, the electron transfer chain is located in the mitochondrial membranes and produces adenosine triphosphate (ATP). In anaerobes, the electron acceptor is C0 , S, sulphate or nitrate ions 2 instead of 02.

This text shows that cell membranes vary according to the 24th cycle: it deals with circadian changes in membrane composition, principally the plasma membrane and with structural organization changes in some chloroplast thylakoids. It deals with changes in: activity or efficiency of pumps, channels, photo- and hormone receptors; sensitivity towards external signals; sensitivity to some drugs, including anaesthetics; and signal transduction. The cell cycle is discussed on theoretical and experimental grounds, as well as its gating by circadian rhythmicity. The rhythm generating mechanism is modelized. The circadian oscillation of the plasm membrane confers a temporal parameter.

Rambling of an elderly biochemist Most biochemists of my generation, who were trying to discover the pathways of metabolism, simply ignored membranes; or regarded them as a nuisance. Think of the difficulties experienced in studies on cytochromoxidase which one could not separate from « insoluble material )} or again of the desperate efforts during a quarter of a century to unravel oxidative phosphorylation without paying much attention to lipidic membranes, altough the system was known to be associated with them. Hence the amazement and the general skepticism that met at first Mitchell''s theory, which was giving membranes the central function they deserve in oxidative phosphorylation and photosynthesis. This, I believe, was a turning point; enzymologists thereafter became aware of the importance of the membranes. Neurophysiologists, of course, had long been interested in the outer cell membrane with its electrical properties and the ion potentials. Histologists and electronmicroscopists also, who observed inside the cell.organelles of which membranes are essential components: nucleus, nucleoli, mitchondria, lysosomes,Golgi apparatus, endoplasmic reticulum, chloroplasts. For them at least, a cell did not look like a mere bag full of enzymes and small molecules; they knew, they could see that it is a highly structured system divided into many compartments by membranous formations.

Although the term redox covers an important number of chemical reactions, biochemists are more familiar with reactions involving the reactions mediated by electron transfer chains associated with respiration, the thiol-disulfide exchanges and the reactions occurring in the presence of free radicals. More recently, the importance of these reactions in the living world and in medicine has been recognized by biochemists, biologists, physiologists, physicians, etc. The importance of the subject in both fundamental and is reflected by the abundance of interesting reviews applied science concerning the subject (Cadenas, 1989, Del Maestro, 1991) and books (Dreosti, 1991; Rice-Evans and Burdon, 1994; Armstrong, 1994) The aim of this chapter is to describe basic reactions known with references to reviews covering special subjects related to redox reactions. Transformation of energy in living organisms is mediated by complex biological systems such as electron transfer chains where the succession of redox reactions provides energy to the organisms. Molecular oxygen or dioxygen is an essential molecule and is the terminal acceptor of electrons during respiration in eukaryotes. In these organisms, the electron transfer chain is located in the mitochondrial membranes and produces adenosine triphosphate (ATP). In anaerobes, the electron acceptor is C0 , S, sulphate or nitrate ions 2 instead of 02.

Although the term redox covers an important number of chemical reactions, biochemists are more familiar with reactions involving the reactions mediated by electron transfer chains associated with respiration, the thiol-disulfide exchanges and the reactions occurring in the presence of free radicals. More recently, the importance of these reactions in the living world and in medicine has been recognized by biochemists, biologists, physiologists, physicians, etc. The importance of the subject in both fundamental and is reflected by the abundance of interesting reviews applied science concerning the subject (Cadenas, 1989, Del Maestro, 1991) and books (Dreosti, 1991; Rice-Evans and Burdon, 1994; Armstrong, 1994) The aim of this chapter is to describe basic reactions known with references to reviews covering special subjects related to redox reactions. Transformation of energy in living organisms is mediated by complex biological systems such as electron transfer chains where the succession of redox reactions provides energy to the organisms. Molecular oxygen or dioxygen is an essential molecule and is the terminal acceptor of electrons during respiration in eukaryotes. In these organisms, the electron transfer chain is located in the mitochondrial membranes and produces adenosine triphosphate (ATP). In anaerobes, the electron acceptor is C0 , S, sulphate or nitrate ions 2 instead of 02.

This text shows that cell membranes vary according to the 24th cycle: it deals with circadian changes in membrane composition, principally the plasma membrane and with structural organization changes in some chloroplast thylakoids. It deals with changes in: activity or efficiency of pumps, channels, photo- and hormone receptors; sensitivity towards external signals; sensitivity to some drugs, including anaesthetics; and signal transduction. The cell cycle is discussed on theoretical and experimental grounds, as well as its gating by circadian rhythmicity. The rhythm generating mechanism is modelized. The circadian oscillation of the plasm membrane confers a temporal parameter.

Rambling of an elderly biochemist Most biochemists of my generation, who were trying to discover the pathways of metabolism, simply ignored membranes; or regarded them as a nuisance. Think of the difficulties experienced in studies on cytochromoxidase which one could not separate from « insoluble material )} or again of the desperate efforts during a quarter of a century to unravel oxidative phosphorylation without paying much attention to lipidic membranes, altough the system was known to be associated with them. Hence the amazement and the general skepticism that met at first Mitchell''s theory, which was giving membranes the central function they deserve in oxidative phosphorylation and photosynthesis. This, I believe, was a turning point; enzymologists thereafter became aware of the importance of the membranes. Neurophysiologists, of course, had long been interested in the outer cell membrane with its electrical properties and the ion potentials. Histologists and electronmicroscopists also, who observed inside the cell.organelles of which membranes are essential components: nucleus, nucleoli, mitchondria, lysosomes,Golgi apparatus, endoplasmic reticulum, chloroplasts. For them at least, a cell did not look like a mere bag full of enzymes and small molecules; they knew, they could see that it is a highly structured system divided into many compartments by membranous formations.

Although the term redox covers an important number of chemical reactions, biochemists are more familiar with reactions involving the reactions mediated by electron transfer chains associated with respiration, the thiol-disulfide exchanges and the reactions occurring in the presence of free radicals. More recently, the importance of these reactions in the living world and in medicine has been recognized by biochemists, biologists, physiologists, physicians, etc. The importance of the subject in both fundamental and is reflected by the abundance of interesting reviews applied science concerning the subject (Cadenas, 1989, Del Maestro, 1991) and books (Dreosti, 1991; Rice-Evans and Burdon, 1994; Armstrong, 1994) The aim of this chapter is to describe basic reactions known with references to reviews covering special subjects related to redox reactions. Transformation of energy in living organisms is mediated by complex biological systems such as electron transfer chains where the succession of redox reactions provides energy to the organisms. Molecular oxygen or dioxygen is an essential molecule and is the terminal acceptor of electrons during respiration in eukaryotes. In these organisms, the electron transfer chain is located in the mitochondrial membranes and produces adenosine triphosphate (ATP). In anaerobes, the electron acceptor is C0 , S, sulphate or nitrate ions 2 instead of 02.