5.4 : Active Transport Flashcards
Define active transport
The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration.
Why does active transport require 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.
Describe the process of active transport
The molecule or ion binds to receptors in the channel of the carrier protein on the outside of the cell.
On the inside of the cell, ATP binds to the carrier protein and is hydrolysed into ADP and phosphate.
Binding of the phosphate molecule to the carrier protein caused the protein to change shape - opening up to the inside of the cell.
The molecule or ion is released to the inside of the cell.
The phosphate molecule is released from the carrier protein and recombines with ADP to form ATP.
The carrier protein returns to its original shape.
Why is active transport selective?
Specific substances are transported by specific carrier proteins
What is bulk transport?
Another form of active transport.
Large molecules such as enzymes, hormones, and whole cells like bacteria are too large to move through channel or carrier proteins, so they are moved into and out of the cell by bulk transport.
What is endocytosis ? What are the types?
Requires ATP.
It is the bulk transport of material into cells.
Two types : phagocytosis ( for solids ) and pinocytosis ( for liquids )
Describe the process of endocytosis
The cell-surface membrane first invaginate ( 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 the material for further processing within the cell.
( eg vesicles containing bacteria are moved towards lysosomes where the bacteria are digested by enzymes )
What is exocytosis? Describe the process.
It is the bulk transport of material out of cells.
Vesicles, usually formed by the Golgi apparatus, move towards and fuse with the cell surface membrane.
The contents of the vesicles are then released outside of the cell.
Why is ATP required for endocytosis / exocytosis ?
For the 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.
