Cell organelles that are double membrane-bound are
- Mitochondria
- Chloroplasts
Its a double membrane-bound structure with the outer membrane and the inner membrane dividing its lumen distinctly into two aqueous compartments i.e. outer compartment and inner compartment. The inner compartment is called ‘matrix’. The inner membrane forms a number of infolding called the cristae towards the matrix. Two membranes have their own specific enzymes associated with the mitochondrial function. Mitochondria are the sites of aerobic respiration.
They produce cellular energy in the form of ATP and called ‘power house’ of the cell. The matrix also possesses single circular DNA molecule, a few RNA molecules, ribosomes (FOS) and the components required for the synthesis of proteins.
Chloroplasts are the plastids that contain chlorophyll pigments which are present in plant cells and euglenoids. The space limited by the inner membrane of the chloroplast is called the ‘stroma’. Stroma contains number of organised flattened membranous sacs called the thylakoids. Thylakoids are arranged in stacks called ‘grana’. Different grana are connected by flat membranous tubules called stroma lamellae. Space inside thylakoids is called lumen.
The stroma of the chloroplast contains enzymes required for the synthesis of carbohydrates and proteins. Its the site of dark reaction. Chlorophyll pigments are present in the thylakoids which along with carotenoid pigments are responsible for trapping light energy essential for photosynthesis. Grana is the site of light reaction.
