Explain the structure of Chloroplast?

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Please find your answer below to the asked query :

Plastid which is green in colour is Chloroplast. It is involved in photosynthesis. 

  • Location: Mesophyll cells in leaves

  • Can be variable in shape (oval/spherical/discoid/ribbon-like), in length and in number (1 per cell in Chlamydomonas to 20−40 per cell in green algae)

  • Have double membrane: Outer membrane and Inner membrane (less permeable)

  • Stroma: Space enclosed by the inner membrane; contains enzymes required for carbohydrate and protein syntheses

  • Thylakoids: Flattened, membrane-bound sacs present in the stroma; contains chlorophyll pigment

  • Grana: Integrated thyllakoids; like piles of coins, where thyllakoids are arranged in stacks

  • Stroma Lamella: Flat, membrane-bound tubules; connect thylakoids present in the different grana

  • Lumen: Space present in thylakoid, i.e., the space enclosed by the thylakoid membrane

  • Stroma of the chloroplast has small, circular DNA and ribosomes (70s).


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All chloroplasts have at least three membrane systems—the outer chloroplast membrane, the inner chloroplast membrane, and the thylakoid system. Chloroplasts that are the product of secondary endosymbiosis may have additional membranes surrounding these three. Inside the outer and inner chloroplast membranes is the chloroplast stroma, a semi-gel-like fluid that makes up much of a chloroplast's volume, and in which the thylakoid system floats.

The chloroplast double membrane is also often compared to the mitochondrial double membrane. This is not a valid comparison—the inner mitochondria membrane is used to run proton pumps and carry out oxidative phosphorylation across to generate ATP energy. The only chloroplast structure that can considered analogous to it is the internal thylakoid system. Even so, in terms of "in-out", the direction of chloroplast H+ ion flow is in the opposite direction compared to oxidative phosphorylation in mitochondria. In addition, in terms of function, the inner chloroplast membrane, which regulates metabolite passage and synthesizes some materials, has no counterpart in the mitochondrion.


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