Chloroplasts membrane structures

Murakami S and Packer L (1970) Protonation and chloroplast membrane structure. 1 Cell Biol 47 332-351... 

Ji TH, Hess JL and Benson AA (1968) Studies on chloroplast membrane structure. I.Association of pigments with chloroplast lamellar protein, Biochim.Biophys.Acta 150, 676-685. 

The photosynthetic apparatus in green plants and algae is located in the chloroplast, which is a flattened, double-membraned structure about 150-200 A thick/4,5 The two flat membranes lie one above the other and are united at their peripheries. These double-membraned structures have been termed thylakoids (from the Greek sacklike )/ Each membrane of the thylakoid consists of a water-insoluble lipoprotein complex which contains the light-absorbing chlorophyll and other pigments utilized in photosynthesis. 

In spite of the variety of appearances of eukaryotic cells, their intracellular structures are essentially the same. Because of their extensive internal membrane structure, however, the problem of precise protein sorting for eukaryotic cells becomes much more difficult than that for bacteria. Figure 4 schematically illustrates this situation. There are various membrane-bound compartments within the cell. Such compartments are called organelles. Besides the plasma membrane, a typical animal cell has the nucleus, the mitochondrion (which has two membranes see Fig. 6), the peroxisome, the ER, the Golgi apparatus, the lysosome, and the endosome, among others. As for the Golgi apparatus, there are more precise distinctions between the cis, medial, and trans cisternae, and the TGN trans Golgi network) (see Fig. 8). In typical plant cells, the chloroplast (which has three membranes see Fig. 7) and the cell wall are added, and the lysosome is replaced with the vacuole. 

The photosynthetic apparatus is found in and on membrane structures, which, in plant cells and algae, are located in chloroplasts and are called thylakoids. In bacteria the photosynthetic membrane is derived by complex invagination of the cytoplasmic membrane. The photosynthetic apparatus is made up of antennae, which contain light-harvesting pigment molecules (usually chlorophylls or bacteriochlorophylls) and photochemical reaction centres, which also contain pigments, together with the necessary enzymes and coenzymes. 

Figure 4 shows a typical ultrastructure of hairy root cells observed under an electron microscope. In the case of photomixotrophic hairy roots, a plastid with a chloroplast-like structure was observed in the light-grown root cells, being associated with thylakoid membranes and grana stacks the particles in the vi-... 

Fig. 4A-C. Electron micrographs of thin sections of pak-bung hairy roots A photomixotro-phic hairy roots obtained from a 13 days culture in light at 7=11.1 W nr2) B, C photo-autotrophic hairy roots cultivated in the sucrose-free medium with 3.0% C02-enriched air supply for 30 days using conical flasks illuminated at 7= 11 W m-2 and shaken at 100 rpm. The abbreviations of 1-3 indicates a chloroplast-like structure with thylakoid membranes and grana stacks (1), chloroplasts (2) and cell walls (3), respectively...

Several reports of the effects of ozone in vivo are presented in Table XII. It is impossible to decide whether the effects of ozone are primary reactions or the result of a series of reactions initiated by ozone. All results can be rationalized as enzyme inhibition of one sort or another. Effects on membrane structure are harder to observe, and in one case it was reported that the malonaldehyde which would be expected on fatty acid ozonolysis was only observed after symptoms were apparent (74). Results of electron microscope examination showed that the first observable damage was in the stroma of the chloroplasts (70). One can easily argue that earlier damage could not be detected by microscopic techniques. However, recent reports that the chloroplast polyribosomes are much more susceptible to degradation by ozone are important observations which are consistent with the microscopy experiments (76). Chloroplast polysomes are also more susceptible to sulfhydryl reagents than are cytoplasmic polysomes (77). This evidence indicates that ozone itself, or a toxic product from primary oxidation, can pass through the cytoplasm and have its effect in the chloroplast. 

From the mere fact that CF, can be released from the membrane by EDTA treatment and the enzyme stays in solution without detergents, it is apparent that the catalytic sector has minimal, if any, direct interaction with the lipids of the chloroplast membrane. It is a globular protein that is held to the surface of the membrane via interaction with the membrane sector. Recently it was shown that the y subunit is in immediate contact with the membrane sector and the 8 and e subunits may induce proper binding for catalysis [17,18], The enzyme contains a few well-defined sites that were used for localization experiments by the method of fluorescent energy transfer [19,56-61], These studies revealed the position of those sites and helped to localize the various subunits of CF, in space relative to the chloroplast membranes (for a model of CF, see Refs. 61 and 62). These experiments are awaiting analysis of the amino acid sequence of the y subunit that is now under investigation in Herrmann s laboratory [148], Definite structural analysis could be obtained only after good crystals of the enzyme become available. 

The membranous structure in the interior of a chloroplast that is the site of... 

Fig. 13. Thylakoid-membrane structure. (A) a (spinach) leaf and (B) a cross-sectional view of the leaf (C) an electron micrograph of a single chloroplast and (O ) a sketch showing idealized structure of a chloroplast (D) magnified view of a portion of the chloroplast interior and (O ) a sketch showing a portion of the thylakoids. See text for discussion. (C) and (D) kindly furnished by Dr. Andrew Staehelin (D ) from Anderson and Beardall (1991) Molecular Activities of Plant Cells. An Introduction to Plant Biochemistry, p 42. Blackwell Sci Publ.

Fig. 19. Chloroplast thylakoid-membrane structure revealed by freeze-fracture electron microscopy. The oxygen-evolving (BBY) PS-II particle its preparation (A) and electron micrographs (B). The inside-out and rightside-out vesicles preparation, structure, and properties (C) and electron micrographs (D). Figure source (A) and (B) Dunahay, Staehelin, Seibert, Ogilvie and Berg (1984) Structural, biochemical and biophysical characterization of four oxygen-evolving photosystem II preparations from spinach. Biochim Biophys Acta 764 190, 185 (C) and (D) from Andersson and Akerlund (1978) Inside-out membrane vesicles isolated from spinach thylakoids. Biochim Biophys Acta 503 465, 468. Figure (B) kindly furnished by Dr. Andrew Staehelin.

The chloroplast, a plant organelle, is the site of photosynthesis in higher plants and algae. Like mitochondria, chloroplasts carry their own DNA to code for some of their proteins, as well as the ribosomes necessary for translation of the appropriate mRNAs. Chloroplasts may have evolved from cyanobacteria, which have membrane structures like chloroplast membranes. 

The internal structure of chloroplasts (Figure 17.4c) resembles that of the mitochondrion (see here). Note the presence of an outer, relatively permeable membrane and an inner membrane that is selectively permeable. The stroma of the chloroplast is analogous to the mitochondrial matrix. Immersed in the stroma are many flat, saclike membrane structures called thylakois which are stacked like coins. The stacks are called grana. Grana are irregularly interconnected by thylakoid extensions called stroma lamellae. The thylakoid membrane encloses the lumen (or interior) of the thylakoid. 

Grana are structures within chloroplasts consisting of stacks of flat, membrane structures (thylakoids). Grana appear as if they were stacks of coins inside the chloroplasts (Figure 17.4c). 

---