Bulky substances are transported into and out of the cell by endocytosis and exocytosis.
Endocytosis:
This is the infolding of the cell membrane to form vesicles. A portion of the membrane invaginates to envelope the contents and draw them into the cell. Once inside, the vesicles are known as intracellular vesicles.
There are 3 types of endo-:
1. Phagocytosis (cell eating)
When a bacterium or other solid item is engulfed by a cell membrane, the intracellular vesicle that was hence formed comes into contact with a lysosome. The lysosome fuses its membrane with the vesicle to release its catabolic enzymes which break down the solid.
2. Pinocytosis (cell drinking)
This occurs when a liquid is engulfed by a cell. In cells with multiple microvilli, such as the intestinal epithelial cells, there are pinocytosis channels between the microvilli which are constantly budding off vesicles of liquid. The cell membrane wraps around a fluid and pinches off, drawing in the liquid in a vesicle, the contents of which are then either broken down or absorbed into the cytosol.
3. Receptor Mediated Endocytosis.
This is a very specific type of pinocytosis because it involves receptors….
Falling asleep now, so I’ll finish this off tomorrow. 🙂
mybiochem 