Question

Write the definition of Endocytosis( include all three of them) and the definition of pinocytosis.

Draw the diagrammatic representation of endocytosis and pinocytosis.

Answer 1

Endocytosis is the ability of eukaryotic cells to take up macromolecules and particles from the surrounding medium. The material to be internalized is surrounded by an area of plasma membrane. This plasma membrane then buds off inside the cell forming a vesicle containing the ingested material. There are three types of endocytic mechanism:

1) Phagocytosis: Phagocytosis is the engulfment of large particles such as bacteria, cell debris, or even intact cells by a cell. When these particles bind to receptors on the surface of the phagocytic cell, the cell will extend their pseudopodia to surround the particle. The membranes fuse to form a large intracellular vesicle, the phagosome. The phagosomes fuses with lysosomes to form the phagolysosomes. In the phagolysosomes, the ingested material is digested by lysosomal acid hydrolases. Some of the internalized membrane proteins are recycled to plasma membrane during maturation of the phagolysosome for receptor-mediated endocytosis.

2) Receptor-mediated endocytosis: Receptor mediated endocytosis is endocytosis of molecules such as hormones, antibodies and other proteins, and lipids to specific receptors in the plasma membrane.

The macromolecules to be internalized bind to specific cell surface receptors. That are concentrated in specialized regions of the plasma membrane, called clathrin-coated pits. These pits bud from the membrane to form small clathrin-coated vesicles. Clathrin coated vesicles fuse with early endosomes From the early endosomes, their contents are sorted and transported transport to lysosomes. They can also be recycled to the plasma membrane.

3. Pinocytosis: Pinocytosis (literally, “cell drinking”) is a process by which a cell takes in small amounts of extracellular fluid along with its solute molecules.

In folding of the cell membrane along with the extracellular fluid (with solute particles) occurs by invagination. Pinocytosis involved ingestion of particles that are already been broken down into small particles. Vesicles called pinosome are formed that are smaller in size. Some energy is generated in form of ATP.

Pinocytosis is a form of endocystosis. Hence, it is a part of the diagram for endocytosis.