Active transport and co transport

active transport definition

The movement of molecules or ions into or out of cells against a concentration gradient to a region of low to high concentration using ATP and carrier proteins

what happens in direct active transport?

• Molecule or ion binds to receptor sites on the specific carrier protein

• ATP binds to the protein and breaks down into ADP and Pi inside the cell

• This releases the energy for the protein to change shape and releases the molecule to the other side of the membrane

• Phosphate molecule is released from protein, causing it to revert to its normal shape

difference between active transport and facilitated diffusion across carrier proteins:

• facilitated diffusion is when particles move down a concentration gradient, while active transport occurs against one

• this means facilitated diffusion does not require metabolic energy, while active transport does get this energy from the breakdown of ATP

what are co transporters and what do they do?

• co transporters are a type of carrier protein, which binds two molecules at time

• the concentration gradient of one of these molecules is used to move the other molecules against its conc gradient

• in sodium-glucose co transporters, sodium moves with its conc gradient and carries glucose with it against its conc gradient

explain the sodium potassium pump:

• sometimes two molecules are moved in same direction at same time and sometimes one molecule is moved into the cell while the other molecule is removed from it

• in the sodium potassium pump, sodium ions are actively removed from cell while potassium ions are actively taken in from outside

Explain the co transport and absorption of glucose into the bloodstream in the small intestine:

1) sodium ions are actively transported out of the epithelial cells in the ileum into the blood, by the sodium-potassium pump (potassium ions taken up by cell) - this takes place in a carrier protein found in the csm of the protein

this creates a concentration gradient - there is now a higher conc of sodium ions in the lumen of the ileum than in the epithelial cells

2) this conc gradient causes sodium ions to diffuse from the lumen into the cell down their conc gradient via the sodium-glucose transporter proteins (moving sodium ions down its conc gradient also moves glucose with it against its conc gradient- this means it is an indirect form of active transport as rather than ATP being used to move glucose against its conc, its the sodium ion conc

so glucose is carried with the sodium into the cell- concentration of glucose inside cell increases

3) glucose then diffuses out of the cell into the blood down its conc gradient through a PROTEIN CHANNEL, by facilitated diffusion

factors affecting the rate of active transport:

• the speed of individual carrier proteins , faster they work= faster rate

• number of carrier proteins present

• rate of respiration in cells and availability of ATP , if respiration inhibited, active transport stops