Structure of chloroplast

     The chloroplast is bounded by two unit membranes, outer and inner lipoproteins membranes with an inter-membrane space between them. The intermembrane encloses stroma or matrix which is da enser, colorless, and granular ground substance. The stroma is mainly formed of proteins (more than 50%) and also 70’s ribosome (plastid-ribosome, circular and naked DNA molecules (0.5%), mRNA and tRNA molecules, water, minerals (mn⁺⁺, Fe⁺⁺, Mg⁺⁺) and enzymes. It is the site of dark reactions of the photosynthesis.

                                                    In the stomata, small structures called grana and inter grana connecting membranes remain embedded. Each granum consists of disc-shaped membranous sacs called thylakoids piled one upon other. The grants are connected by a network of membranous tubules known as the integrand or stroma lamellae or frets. The thylakoid membrane contains all the enzymatic quantasomes components required for photosynthesis. They are the site of light reactions. Interaction between chlorophyll and other components takes place within the thylakoid membrane. Like mitochondria, chloroplasts are semi-autonomous cell organelles because they have complete machinery to synthesize some of the required proteins while some other proteins depend upon nuclear DNA and cytoplasmic ribosomes.