Photosynthesis chloroplasts

Chlorenchyma Parenchyma cells containing chloroplasts Photosynthesis... 

The requirement of chloroplast photosynthesis for Pj and the release of Pj by sucrose synthesis in the cytosol require that these two processes be closely coordinated. Part of this coordination, as explained above, lies in the characteristics of the triose phosphate translocator. Results obtained in the last few years have led to the identification of a second component serving this function. Fructose 2,6-bis-phosphate (Fru-2,6-P2) coordinates the metabolism of sucrose, starch and CO2 fixation and, in so doing, links metabolic processes of the chloroplast with those of the cytosol. 

In view of the endosymbiotic theory no further explanation is needed for the detailed similarity between mitochondrial respiration and that of some eubacteria, nor for the striking resemblance of chloroplast photosynthesis to that of cyanobacteria. 

In the chloroplasts, photosynthesis proceeds with the aid of the light energy received. Carbohydrates (sugar, starch) are formed from carbon dioxide and water and oxygen are liberated. In an aqueous algal suspension the oxygen liberated can easily be observed in the form of bubbles. 

Chlorophylls.—Aspects of the primary processes of photosynthesis which have recently been reviewed include excitation energy transfer in photosynthesis,376 primary photochemical reactions in chloroplast photosynthesis,373 light-induced paramagnetism in photosynthetic systems,377 and photosynthetic reaction centres and primary photochemical reactions.378... 

Below the calculation routines to calculate the average specific rate of sugar production in the chloroplast (photosynthesis) wiU be explained in more detail for the Blackman andjassby Platt models. In order to perform such calculations aU necessary biological parameters must be known for the microaigai species to be cultivated a Ts/ph,m qlm, Yk/,, m,. 

The above considerations make it seem probable that mitochondrial ATP synthesis has an important function to serve during photosynthesis the ATP demand of the cytosol. The essential function of mitochondrial ATP synthesis in photosynthesis metabolism has been demonstrated by its selective inhibition by oligomycin. Whereas the addition of low concentrations of this inhibitor did not affect the photosynthesis of isolated chloroplasts, photosynthesis of protoplasts was inhibited by up to 50% (16). As shown in table 3, the decrease of photosynthesis of whole protoplasts is accompanied by a marked increase of glucose-6-phosphate and a decrease of the ATP level specifically in the cytosol. 

The products formed in chloroplast photosynthesis appear to be similar to those formed in photosjmthesis by intact cells (3a), and it seems reasonable to assume that the COr dng system here is similar to the one discussed earlier. Two facts lend further support to this... 

The leaf structure has several important functions, three of which are photosynthesis, transpiration, and respiration (2). Photosynthesis is accomplished by chloroplasts in the leaf, which combine water and COj in the presence of sunlight to form sugars and release O2. This process is shown in Eq. (8-1). 

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. 

Starch is stored in plant cells in the form of granules in the stroma of plas-tids (plant cell organelles) of two types chloroplasts, in which photosynthesis takes place, and amyloplasts, plastids that are specialized starch accumulation bodies. When starch is to be mobilized and used by the plant that stored it, it must be broken down into its component monosaccharides. Starch is split into its monosaccharide elements by stepwise phosphorolytic cleavage of glucose units, a reaction catalyzed by starch phosphorylase (Figure 7.23). This is formally an a(1 4)-glucan phosphorylase reaction, and at each step, the prod-... 

During the 1960s, research on proteins containing iron—sulfur clusters was closely related to the field of photosynthesis. Whereas the first ferredoxin, a 2[4Fe-4S] protein, was obtained in 1962 from the nonphotosynthetic bacterium Clostridium pasteurianum (1), in the same year, a plant-type [2Fe-2S] ferredoxin was isolated from spinach chloroplasts (2). Despite the fact that members of this latter class of protein have been reported for eubacteria and even archaebacteria (for a review, see Ref. (3)), the name plant-type ferredoxin is often used to denote this family of iron—sulfur proteins. The two decades... 

A decade after the discovery of the Rieske protein in mitochondria (90), a similar FeS protein was identified in spinach chloroplasts (91) on the basis of its unique EPR spectrum and its unusually high reduction potential. In 1981, the Rieske protein was shown to be present in purified cytochrome Sg/complex from spinach (92) and cyanobacteria (93). In addition to the discovery in oxygenic photosynthesis, Rieske centers have been detected in both single-RC photosynthetic systems [2] (e.g., R. sphaeroides (94), Chloroflexus (95)) and [1] (Chlo-robium limicola (96, 97), H. chlorum (98)). They form the subject of a review in this volume. 

Krause, G.H. Laasch, H. (1987). Energy-dependent chlorophyll fluorescence quenching in chloroplasts correlated with quantum yield of photosynthesis. Zeitschrift fiir Naturforschung, 42, 581. ... 

Powles, S.B. Bjorkman, O. (19826). Photoinhibition of photosynthesis effect on chlorophyll fluorescence at 77 K in intact leaves and chloroplast membranes of Nerium oleander. Planta, 156, 97-107. 

Photosynthesis is the reverse of reaction (30.1) the formation of carbohydrates and oxygen from water and carbon dioxide with solar energy. Photosynthesis occurs in the chloroplasts contained in the cells of green plants. The chloroplasts hold two types of photosynthetic systems, which are called PSl and PS 11. These systems... 

The individual steps of the multistep chemical reduction of COj with the aid of NADPHj require an energy supply. This supply is secured by participation of ATP molecules in these steps. The chloroplasts of plants contain few mitochondria. Hence, the ATP molecules are formed in plants not by oxidative phosphorylation of ADP but by a phosphorylation reaction coupled with the individual steps of the photosynthesis reaction, particularly with the steps in the transition from PSII to PSI. The mechanism of ATP synthesis evidently is similar to the electrochemical mechanism involved in their formation by oxidative phosphorylation owing to concentration gradients of the hydrogen ions between the two sides of internal chloroplast membranes, a certain membrane potential develops on account of which the ATP can be synthesized from ADP. Three molecules of ATP are involved in the reaction per molecule of COj. 

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