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General Features of Photophosphorylation: - Photosynthesis in Plants Takes Place in Chloroplasts

المؤلف:  David L. Nelson، Michael M. Cox

المصدر:  Lehninger Principles of Biochemistry

الجزء والصفحة:  724

2026-06-23

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General Features of Photophosphorylation:- Photosynthesis in Plants Takes Place in Chloroplasts

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 in ternal 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) con tains most of the enzymes required for the carbon assimilation reactions.

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