5.4 Active Transport Flashcards
Definition of active transport
The movement of a substance (molecules or ions) from a region where it is in a low concentration to a region where it is in a high concentration. This process requires the expenditure of metabolic energy in the form of ATP and carrier proteins
What is a carrier protein?
A protein completely spanning the phospholipid bilayer which binds to ions or molecules then change shape in order to move these molecules across the membrane
Explain the process of active transport using this diagram
- The molecule or ions to be transported 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 a phosphate
- Binding on the phosphate molecule to the carrier protein causes the protein to change shape, opening up to the inside of the cell ATP
- The molecule or ions is released to the inside of the cell ATP binds
- The phosphate molecule is released from the carrier protein and recombines with ADP to form ATP
- The carrier protein returns to its original shape
Is active transport an active or passive process?
Active, requires energy from ATP to move molecules from low to high concentration
What is ATP hydrolysed into?
ADP, Phosphate, energy
What is co-transport?
The transport of one substance coupled with the transport of another substance across a plasma membrane in the same direction through the same carrier protein
What is an example of co-transport in the body?
Co-transport of glucose in the small intestine
Explain how co-transport of glucose occurs at the small intestine (at the ileum)
- Na+ ions are actively transported out of the epithelial cells in the ileum into the blood by the sodium-potassium pump. This creates a concentration gradient as there are more sodium ions in the lumen of the ileum than inside the epithelial cells (antiport)
- The concentration gradient causes Na+ ions to diffuse from the lumen of the ileum into the epithelial cell down their concentration gradient. They do this through the Na+-glucose cotransporter protein. Glucose enters the cell with sodium (synport)
- There is a higher concentration of glucose inside the epithelial cell than in the blood so glucose diffuses into the blood down its concentration gradient through a protein channel by facilitated diffusion
What are the factors affecting the rate of active transport?
Speed of carrier proteins, Number of carrier proteins, Rate of respiration
How does the speed of carrier proteins affect the rate of active transport?
The faster they work, the faster the rate of active transport
How does the number of carrier proteins affect the rate of active transport?
The greater the number of carries proteins in the plasma membrane, the faster the rate of active transport.
How does the rate of respiration affect the rate of active transport?
The greater the rate of respiration the more ATP there will be avaliable for active transport. ATP is produced by aerobic respiration in the mitochondria, active transport therefore depends on the rate of respiration. Oxygen is therefore required for active transport to occur
Definition of bulk transport
A form of active transport where large molecules or whole bacterial cells are moved into or out of a cell by endocytosis or exocytosis
What types of molecules require bulk transport?
Large molecules such as enzymes, hormone and whole cells like bacteria which are too large to move through channel or carrier proteins
Does bulk transport require energy?
Yes, in the form of ATP to move vesicles
What are the two types of endocytosis?
Phagocytosis for solids, Pinocytosis for liquids
Definition of endocytosis
The bulk transport of material into cells via invagination of the cell-surface membrane forming a vesicle
Definition of exocytosis
The bulk transport of materials out of the cells. Vesicles containing the material fuse with the cell-surface membrane and the contents are released to the outside of the cell
What is the process of endocytosis?
The cell-surface membrane first invaginates (bends inwards) when it first comes into contact with the material that is being transported. The membrane enfolds the material eventually the memebrane fuses, forming a vesicle. The vesicle pinches off and moves into the cytoplasm
What is the process of exocytosis?
Vesicles usually formed by the golgi apparats move towards and fuse with the cell surface membrane. The contents of the vesicle are released outside of the cell
What is the difference between active transport and facilitated diffusion?
They both use carrier proteins but facilitated diffusion occurs down its concentration gradient and therefore does not require energy
What is cell-mediated endocytosis?
Endocytosis which uses receptor proteins on the cell surface to capture a specific target molecule. When the receptor binds to the target molecule endocytosis is triggered
What is an example of exocytosis?
Neurotransmitters
