Chloroplast

Chloroplast

  • Most of the chloroplasts in green plants are found in the mesophyll cells of the leaves. 
  • They can have various shapes, including lens-shaped, oval, spherical, discoid, or ribbon-like, with variable length and width (typically 5-10µm in length and 2-4µm in width). 
  • Like mitochondria, chloroplasts are also double-membrane-bound organelles. 
  •  The inner membrane is relatively less permeable. 
  • The space enclosed by the inner membrane is known as the stroma.

Thylakoids and Grana: 

- Chloroplasts contain organized, flattened membranous sacs called thylakoids, which are present in the stroma.

- Thylakoids are arranged in stacks like piles of coins, known as grana (singular: granum), and the membranes connecting thylakoids are called stroma lamellae.

- Thylakoids enclose a space known as a lumen.

- The stroma of the chloroplast contains enzymes necessary for the synthesis of carbohydrates and proteins. 

Genetic Material:

- Chloroplasts contain small, double-stranded circular DNA molecules and ribosomes.

- Notably, the ribosomes in chloroplasts are smaller (70S) than the cytoplasmic ribosomes (80S).