Metabolism photosynthesis

Recent years have witnessed increasing interest in the biology, chemistry, and physics of electron-transferring non-heme iron proteins. This class of protein serves as an oxidation-reduction component in various biological functions involved in anaerobic fermentative metabolism, photosynthesis, and hydroxylation reactions. 

Approximately one-third of all proteins in the human body contain metals. These and other metalloproteins are essential for the basic processes of life, including DNA synthesis, metabolism photosynthesis detoxification, and the chemical transformations of nitrogen, oxygen, and carbon molecules required for life. Many diseases are due to metal imbalances or inactivity of critical metalloproteins. In fact, numerous essential biological functions require metal atoms. Thus, metalloproteins make life on Earth possible and the ability to understand and ultimately control the binding and activity of protein metal sites is of great biological and medical importance. 

M. Gibbs and E. Lat2ko, eds.. Photosynthesis 11 Photosynthetic Carbon Metabolism and Kelated Processes, Tnyclopedia of Plant Physiology, N.S., Springer-Vedag, Berlin, 1979. 

Except as an index of respiration, carbon dioxide is seldom considered in fermentations but plays important roles. Its participation in carbonate equilibria affects pH removal of carbon dioxide by photosynthesis can force the pH above 10 in dense, well-illuminated algal cultures. Several biochemical reactions involve carbon dioxide, so their kinetics and equilibrium concentrations are dependent on gas concentrations, and metabolic rates of associated reactions may also change. Attempts to increase oxygen transfer rates by elevating pressure to get more driving force sometimes encounter poor process performance that might oe attributed to excessive dissolved carbon dioxide. 

Physiological or biochemical changes have been observed in plants exposed to air pollutants, including alterations in net photosynthesis, stomate response, and metabolic activity. Such exposure studies have been conducted under controlled laboratory conditions. An understanding of the processes involved will help to identify the cause of reduction in yield. 

Injury any physical or biological response to pollutants, such as a change in metabolism, reduced photosynthesis, leaf necrosis, premature leaf drop, or chlorosis. 

Autotrophy A unique form of metabolism foimd only in bacteria. Inorganic compounds (e.g., NH3, N02-, S2, and Fe2+) are oxidized directly (without using sunlight) to yield energy. This metabolic mode also requires energy for C02 reduction, like photosynthesis, but no lipid-mediated processes are involved. This metabolic mode has also been called chemotrophy, chemoautotrophy, or chemolithotrophy. 

Bacterial Photosynthesis A light-dependent, anaerobic mode of metabolism. Carbon dioxide is reduced to glucose, which is used for both biosynthesis and energy production. Depending on the hydrogen source used to reduce COj, both photolithotrophic and photoorganotrophic reactions exist in bacteria. 

Chloroplasts are the site of photosynthesis, the reactions by which light energy is converted to metabolically useful chemical energy in the form of ATP. These reactions occur on the thylakoid membranes. The formation of carbohydrate from CO9 takes place in the stroma. Oxygen is evolved during photosynthesis. Chloroplasts are the primary source of energy in the light. 

Photosynthesis uses many of the same enzyme-driven steps found in glucose metabolism, only in... 

NEMCA is a triumph, and the latest in a series of advances in electrochemistry which have come about in the last 30 years, all of them situations which are not obviously electrochemical. Examples include corrosion, metabolism, and (part of) photosynthesis. 

Redox reactions constitute the third of the three major classes of chemical reactions treated here. The variety of these reactions is remarkable. Many common reactions, such as combustion, corrosion, photosynthesis, the metabolism of food, and the extraction of metals from their ores, appear to be completely different. However, when we consider these changes at the molecular level with a chemist s eye, we can see that they are all examples of a single type of process. 

Damage to epicuticular waxes Altered photosynthesis Increased water loss Accumulation of acidic anions Leaching of ions, sugars, etc. Mineral imbalances Altered metabolism Increased susceptibility to winter freezing injury Death of fine roots Destabilization of trees Reduced water/mineral uptake Reduced water uptake Cations leached below roots Accumulation of acidic anions Altered structure/texture Altered microflora Reduced litter decomposition Altered N transformations Solubilization of metal ions... 

Altered photosynthesis Altered cell metabolism Damage to foliage cuticles Damage to epicuticular waxes Many foliage effects Altered reproductive patterns Poorly investigated... 

The example we will consider in more detail is that of inducible CAM (Crassulacean acid metabolism). CAM is a modification of photosynthesis... 

An intriguing stress-induced alteration in gene expression occurs in a succulent plant, Mesembryanthemum crystallinum, which switches its primary photosynthetic CO2 fixation pathway from C3 type to CAM (Crassulacean acid metabolism) type upon salt or drought stress (Winter, 1974 Chapter 8). Ostrem et al. (1987) have shown that the pathway switching involves an increase in the level of mRNA encoding phosphoenol-pyruvate carboxylase, a key enzyme in CAM photosynthesis. 

The reported (14) mechanisms of action of allelochemlcals Include effects on root ultrastructure and subsequent Inhibition of Ion absorption and water uptake, effects on hormone-induced growth, alteration of membrane permeability, changes In lipid and organic acid metabolism, inhibition of protein synthesis and alteration of enzyme activity, and effects on stomatal opening and on photosynthesis. Reduced leaf water potential Is one result of treatment with ferulic and p-coumaric acids (15). Colton and Einhellig (16) found that aqueous extracts of velvetleaf (Abutllon theophrastl Medic.) Increased diffusive resistance In soybean fGlycine max. (L.) Merr.] leaves, probably as a result of stomatal closure. In addition, there was evidence of water stress and reduced quantities of chlorophyll In Inhibited plants. 

Although fragmentary evidence points to a linkage to metabolic processes such as photosynthesis and respiration, the mechanisms of phototaxis and phototropism remain largely unknown and must await the results of further research in this very interesting area. 

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