Grana membrane stacking

FIGURE 1. Countercurrent distribution diagram of sonicated stacked thylakoid membranes. The a-peak comprises vesicles originating from the grana membrane and the j5-peak comprises vesicles originating from the stroma membrane. From ref.(l). 

FIGURE 7.3 Structure of PSII membranes, macrocomplexes and LHCII antenna. Left from the top electron microscopy of grana stacks, PSII macrocomplexes, LHCII trimers, and LHCII oligomers. Right from the top Atomic structure of LHCII monomer (I and II are side and top views). Bottom part displays LHCII... 

It is helpful to think of the photosynthesis reaction as the sum of an oxidation half reaction and a reduction half reaction as shown in Figure 1. In fact, nature does separate these half reactions, in that the reduction of C02 to carbohydrates occurs in the stroma of the chloroplast, the organelle in the leaf where the photosynthesis reaction occurs, - whereas, the light-driven oxidation half reaction takes place on the thylakoid membranes which make up the grana stacks within the chloroplast. Reduced nicotinamide adenine dinucleotide phosphate (NADPH) carries the reducing power and most of the energy to the stroma to drive the fixation of C02 with the help of some additional energy provided... 

Chloroplasts (29-36) are the sites of photosynthesis and their ribosomes can carry out protein synthesis. Chloroplasts that contain chlorophylls and carotenoids, are disc shaped and 4-6 pm in diameter. These plastids are comprised of a ground substance (stroma) and are traversed by thylakoids (flattened membranous sacs). The thylakoids are stacked as grana. In addition, the chloroplasts of green algae and plants contain starch grains, small lipid oil droplets, and DNA. 

FIGURE 19-38 Chloroplast. (a) Schematic diagram, (b) Electron micrograph at high magnification showing grana, stacks of thylakoid membranes. 

In photosynthetic eukaryotic cells, both the light-de-pendent and the carbon-assimilation reactions take place in the chloroplasts (Fig. 19-38), membrane-bounded intracellular organelles that are variable in shape and generally a few micrometers in diameter. Like mitochondria, they are surrounded by two membranes, an outer membrane that is permeable to small molecules and ions, and an inner membrane that encloses the internal compartment. This compartment contains many flattened, membrane-surrounded vesicles or sacs, the thylakoids, usually arranged in stacks called grana (Fig. 19-38b). Embedded in the thylakoid membranes (commonly called lamellae) are the photosynthetic pigments and the enzyme complexes that carry out the light reactions and ATP synthesis. The stroma (the aqueous phase enclosed by the inner membrane) contains most of the enzymes required for the carbon-assimilation reactions. 

ATP synthase, whose knobs also protrude into the stroma. A photosynthetic unit can also be defined chemically by the number of various types of molecules present in a chloroplast membrane for each four manganese atoms (Table 23-2). Separate units contain PSI and PSII. These reaction centers appear to have a different distribution within the thylakoids, the PSI units being located principally in the unstacked membranes and the PSII units in the grana stacks.255 259... 

The photosynthesis machinery in the chloroplasts is in a system of thylakoid membranes, which are stacked in arrays called grana. The grana look like a stack of coins. The thylakoid membranes contain enzymes and protein assemblies that contain the chlorophyll. The two kinds of protein assemblies are called photosystem I and photosystem II. These assemblies absorb energy from light. 

Granum (pi. grana) A closely packed stack of thylakoid membranes in a chloroplast. 

Chloroplasts in plant cells are surrounded by a double membrane and have an internal membrane system of thylakoid vesicles that are stacked up to form grana. The thylakoid vesicles contain chlorophyll and are the site of photosynthesis. Carbon dioxide (C02) fixation takes place in the stroma, the soluble matter around the thylakoid vesicles. 

Thylakoid membrane internal membrane system of chloroplasts folded repeatedly into a stack of disks called grana. 

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...

Figure 1 Exploding diagram of the photo synthetic apparatus of a typical higher plant. The first expansion bubble shows a cross-section of a leaf, with the different types of cells the dark spots are the chloroplasts. The second bubble is a chloroplast the thylakoid membranes are the dark lines, the stroma is the stippled area. The third bubble shows a grana stack of thylakoids. The fourth bubble shows a schematic picture of the molecular structure of the thylakoid membrane, with a reaction center flanked by anterma complexes. (Ref. 1. Reproduced by permission of Blackwell)...

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