Bulk Transport

Bulk Transport Some Molecules, such as COMPLEX PROTEINS, FOOD and other substances are too LARGE to cross the cell membrane by diffusion or through transport proteins. 2. These substances cross the membrane by BULK TRANSPORT where they are packaged in membrane bound sacs called vesicles and move out across the membrane to exit the cell, or are formed into vesicles to get into the cell.

THERE ARE SEVERAL TYPES OF BULK TRANSPORT: A. Endocytosis ( movement in) Pinocytosis Phagocytosis B. Exocytosis (movement out)

During ENDOCYTOSIS the cell membrane folds into a POUCH that encloses the particles. The pouch pinches off INSIDE the cell to form a VESICLE (membrane-wrapped bubbles). The VESICLE can then fuse with other organelles (LYSOSOMES) or release its contents into the cytoplasm.

Real cells

Pinocytosis and Phagocytosis are two types of Endocytosis: Pinocytosis is sometimes called “cell drinking” Solutes or fluids outside the cell membrane can be brought into the cytoplasm by PINOCYTOSIS.

Phagocytosis is like Pinocytosis except the cell engulfs a food particle or other cell * It is like "CELL EATING" * The food vesicle can then fuse with a lysosome that contains DIGESTIVE ENZYMES.

*White Blood Cells (Phagocytes) Destroy bacteria and other unwanted cells by phagocytosis. These cells engulf and digest millions of old RBC in your body daily.

There is a special type of endocytosis called Receptor mediated endocytosis This is when a specific molecule binds to receptors on the cell membrane. The binding initiates the cell membrane to pinch in (endocytosis).

EXOCYTOSIS is the reverse of opposite of endocytosis. During exocytosis, waste and cell products leave the cell PRODUCTS LEAVE THE CELL. Products made in the cell are packaged in GOLGI BODY vesicles, which then fuse with the cell membrane and secrete material OUT of the cell. ( usually waste products)

Transport animation http://highered.mcgraw-hill.com/olc/dl/120068/bio02.swf