Eukaryotes photosynthesis

In eukaryotes, photosynthesis takes place in chloroplasts. The light reactions take place in the thylakoid membrane, a third membrane in chloroplasts in addition to the inner and outer membrane. 

Energy transduction in cyanobacteria is poorly understood relative to our understanding of phosphorylation in eukaryotic photosynthesis. As part of a study of electron transport and phosphorylation in the cyanobacterium Spirulina platensis, our laboratory extracted and partially purified a protein with latent Ca-ATPase activity that reconstituted photophosphorylation in ATPase-depleted membranes (Owers-Narhi et al. 1979). In the present report we describe the purification to homogeneity and some of the characteristics of the Spirulina platensis coupling factor Ca-ATPase (SFi). 

In cyanobacteria and the eukaryotic photosynthetic cells of algae and higher plants, HgA is HgO, as implied earlier, and 2 A is O,. The accumulation of O, to constitute 20% of the earth s atmosphere is the direct result of eons of global oxygenic photosynthesis. 

The existence of two separate but interacting photosystems in photosynthetic eukaryotes was demonstrated through analysis of the photochemical action spectrum of photosynthesis, in which the oxygen-evolving capacity as a function of light wavelength was determined (Figure 22.10). 

The eukaryotes these include animals, plants, fungi and protozoa, the DNA of which is enclosed in a membrane-enclosed organelle (the cell nucleus). They have a cytoskeleton (a fine membrane-like network in the interior of the cell, which provides stability) and contain mitochondria. Higher plants, as well as algae, are equipped with chloroplasts for photosynthesis. 

According to the endosymbiotic hypothesis, the eukaryotes used genes from both bacteria (alpha-protobacteria) and cyanobacteria. The first led to the development of mitochondria, the second to that of chloroplasts, i.e., cell organelles which are highly important for energy production (ATP synthesis) and photosynthesis. 

Some of these species can carry out photosynthesis, but they may do so by engulfing symbiotic algae. It has been suggested that Grypania found in iron sediments could be the earliest eukaryotes. 

Long-term aim of our project is the construction of a biomolecular device for hydrogen production in combination with light-driven water-splitting as it occurs in the natural process of photosynthesis in plants. Such a semiartificial device should combine the best suited components found in various native systems which - up to now - cannot be found in an individual native system due to incompatibilities and/or different origin (pro- and eukaryotic, meso- and thermophilic, aerobic - anaerobic environment). Advantage of such a system is... 

Eukaryotic cells acquired the capacity for photosynthesis and for oxidative phosphorylation from endosymbiotic bacteria. 

Fig. 2. An evolution diagram illustrating a suggestion of common ancestry of some present-day organisms. The essential features of present-day photosynthesis may have originated in the prebiotic era and is preserved in its most primitive form in (at least some) present-day phototrophs. The heterotrophs may have developed parallel with the aerobic nonphotosynthetic bacteria, some l to 1.5 x 109 years after the emergence of the cyanobacteria. The eukaryotic photosynthetic organisms developed much later, perhaps some 1.5 to 0.5 x 109 years ago. The archaebacteria are primitive organisms that seem to have no evolutionary relation with the present prokaryotes.21 Little is known about their energy metabolism. Tentatively, they are considered as a very early form of cellular life.

In addition to their plasma membrane eukaryotic cells also contain internal membranes that define a variety of organelles (fig. 17.2). Each of these organelles is specialized for particular functions The nucleus synthesizes nucleic acids, mitochondria oxidize carbohydrates and lipids and make ATP, chloroplasts carry out photosynthesis, the endoplasmic reticulum and the Golgi apparatus synthesize and secrete proteins, and lysosomes digest proteins. Additional membranes divide mitochondria and chloroplasts into even finer, more specialized subcompartments. Like the plasma membrane, organellar membranes act as barriers to the leakage of proteins, metabolites, and ions they contain transport systems for import and export of materials, and they are the sites of enzymatic activities as diverse as cholesterol biosynthesis and oxidative phosphorylation. 

One of the more exciting and recent advances in the field of plant biochemistry has been the discovery of the mevalonate-independent pathway for the biosynthesis of isoprenoids (Fig. 10.4). This new pathway, referred to a the methyl-erythritol-phosphate or MEP pathway for the first intermediate committed solely to the biosynthesis of isoprenoids, was first discovered in prokaryotes capable of accumulating hopenes, the equivalent of eukaryotic sterols. 6,17 The MEP pathway has since been confirmed in plants and, not surprisingly, has been localized to chloroplasts.18 Operation of the MEP pathway is intimately related to the reactions of CO2 fixation and photosynthesis, as evidenced by the two immediate precursors pyruvate and phosphoglyceraldehyde for this pathway. Two important features of this pathway are that mevalonate is not an intermediate in the plastidic synthesis of isopentenyl (IPP) and dimethylallyl diphosphate, (DMAPP), and this pathway... 

Plantae The plant kingdom nonmobile, autotrophic, multicellular eukaryotes. Kingdom of the plants, autotrophic eukaryotes with cellulose in their cell walls and starch as a carbohydrate storage product, with chlorophylls a and b as photosynthesis pigments. 

Hydrogen sulfide is also subject to phototrophic oxidation in anaerobic environments. The photosynthetic sulfur bacteria Chromatiaceae, Ectothiorho-dospimceae, and Chlorobiaceae can photoreduce C02 while oxidizing H2S to S, in a striking analogy with the photosynthesis of eukaryotes ... 

Eukaryotic photosynthetic organisms include various types of algae, mosses, ferns and higher plants. In all these organisms, photosynthesis is confined to a subceUular organelle known as the Chloroplast. In many ways, the chloroplast is similar to certain types of photosynthetic bacteria, and can... 

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