Principles of Biochemistry

1.1.3.8 Other organelles

i.Ribosome: Ribosome is a small organelle composed of RNA-rich cytoplasmic granules that are sites of protein synthesis. Each ribosome has a large and a small subunit. Each subunit contains about 65% RNA and 35% protein.

ii.Lysosome: Lysosome is round organelles surrounded by a membrane and containing digestive enzymes. Lysosomes function in the digestion of materials brought into cell by phagocytosis or pinocytosis. They also serve to digest cell components after cell death.

iii.The Golgi apparatus: The Golgi apparatus consists of flattened, single membrane vesicles. Some become vacuoles in which secretary products are concentrated. The primary function of the Golgi apparatus is to process and package macromolecules, such as proteins and lipids, after their synthesis and before they make their way to their destination. It is important in the processing of proteins for secretion. It has a system of outer flattened cisternae which appear as roughly parallel membranes enclosing a space 60-90Ǻ with a distance of about 200Ǻ between them.

iv. Vacuole: A vacuole is a membrane bound organelle which is present in all plant and fungal cells and some animal and bacterial cells. From the outside, the vacuole is surrounded by tonoplast.Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic molecules including enzymes in solution, though in certain cases they may contain solids which have been engulfed. Vacuoles are formed by the fusion of multiple membrane vesicles and are effectively just larger forms of these.

The functions of the vacuole include: isolation of materials that might be harmful or a threat to the cell, containing waste products, exporting unwanted substances from the cell, maintaining internal hydrostatic pressure or Turgot within the cell and maintaining internal pH.