Active Transport
- Active transport is the movement of molecules and ions through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration
- This process allows cells to establish or maintain concentration gradients as required by the cell
- Active transport requires carrier proteins (each carrier protein being specific for a particular type of molecule or ion)
- Although facilitated diffusion also uses carrier proteins, active transport is different as it requires an additional input: energy
- The energy is required to make the carrier protein change shape, allowing it to transfer the molecules or ions across the cell membrane
- The energy required is provided by ATP (adenosine triphosphate) produced during respiration. The ATP is hydrolyzed to release energy
Active Transport Diagram
Active transport across the cell membrane
Sodium potassium ATPase pumps in axons
- Sodium potassium ATPase is an example of an integral protein pump that enables an electrochemical gradient (resting membrane potential) to be maintained between the inside and outside of the axon
- Nerve impulses that travel along axons are dependent on sodium and potassium ions being moved across the axon membrane to generate this gradient
- The sodium potassium pumps move 3 sodium ions out of the axon and 2 potassium ions into the axon using 1 ATP molecule per cycle
- The pumps are always moving the ions against their concentration gradient via active transport
- The cycle continues until the resting membrane potential is reached
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- 3 sodium ions from the inside of the axon bind to the pump
- ATP attaches to the pump and transfers a phosphate to the pump (phosphorylation) causing it to change shape, resulting in the pump opening to the outside of the axon
- The 3 sodium ions are released out of the axon
- 2 potassium ions from outside the axon enter and bind to their sites
- The attached phosphate is released, altering the shape of the pump again
- The change in shape causes the potassium ions to be released inside the axon
- The steps to this cycle are:
Active Transport in Cells
Active transport of sodium and potassium ions in axons using sodium potassium pump carrier proteins