Chapter 5-5.4- Active transport Flashcards
What is active transport?
Active transport is the movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher of higher concentration.
The process requires energy and carrier proteins.
Energy is needed as the particles are being moved up a concentration gradient, in the opposite direction to diffusion.
Metabolic energy is supplied by ATP.
Carrier proteins span the membranes and act as “pumps”. The general process of active transport is described below- in this example transport is from outside to inside a cell.
1) The molecule or ion to be transported binds to receptors in the channel of the carrier protein on the outside of the cell.
2) On the inside of the cell of the cell ATP binds to the carrier protein and is hydrolysed into ADP and phosphate.
3) Binding of the phosphate molecule to the carrier protein causes the protein to change shape- opening up to the inside of the cell.
4) The molecule or ion is released to the inside of the cell.
5) The phosphate molecule is released from the carrier protein and recombines with ADP to form ATP.
6) The carrier protein returns to its original shape.
The process is selective- specific substances are transported by specific carrier proteins.
What is bulk transport?
Bulk transport is another from of active transport. Large molecules such as enzyme, hormone, and whole cells like bacteria are too large to move through channel or carrier proteins, so they are moved into and out of cell by bulk transport.
What is endocytosis?
Endocytosis is the bulk transport of material into cells. There are two types of endocytosis, phagocytosis for solids and pinocytosis for liquids for liquids- the process is the same for both.
The cell-surface membrane first invalidates (bends inwards) when it comes into contact with the material to be transported.
The membrane enfolds the material until eventually the membrane fuses, forming a vesicle. The vesicle pinches off and moves into the cytoplasm to transfer that material for further processing within the cell.
For example; vesicles containing bacteria are moved towards lysosomes, where bacteria are digested by enzymes.
What is exocytosis ?
The reverse of endocytosis. Vesicles, usually formed by the Golgi apparatus, move towards and fuse with the cell surface membrane. The contents of the vesicle are then released outside of the cell.
What is required for movement of vesicles ?
Energy in the form of ATP is required for movement of vesicles along the cytoskeleton, changing the shape of cells to engulf materials, and the fusion of cell membranes as vesicles form or as they meet the cell-surface membrane.
