H1 Biology and H2 Biology
Endocytosis and Exocytosis
Notes from the video ‘A Level H2 Biology Tuition and H1 Biology Tuition | Endocytosis and Exocytosis’:
In this Biology tutorial, we would learn about the process of endocytosis and exocytosis.
Endocytosis is a process to transport macromolecules or molecules in large quantity into the cell. ATP is required for the rearrangement of microtubules.
There are three types of endocytosis – phagocytosis, pinocytosis and receptor-mediated endocytosis.
For macromolecules, there is phagocytosis where the cell membrane extends out to form the pseudopodia that engulfs the macromolecules. When the ends of the pseudopodia fuse, a vesicle containing the solid matter is pinched off into the cytoplasm.
A tiny vesicle of aqueous medium is brought in when a small area of the plasma membrane invaginates.
Specific molecules binds to the receptor proteins on the cell surface.
The receptor molecule moves to the clathrin-coated pit. The cell membrane folds inwards to form a clathrin-coated vesicle.
The vesicle fuses with an endosome.
The receptors and molecules separate into different vesicles. The molecules is transported to the lysosomes while the receptors are transported to the cell membrane.
Compounds are excreted from cells via exocytosis.
Secretory vesicles are transported towards the membrane along the microtubules and fuses with the membrane, releasing the molecule.