Daily Newsletter January 26, 2012
Today's Topic: Active Transport
In active transport, cells are moving substances across the membrane, but against the chemical concentration. Chemicals are move from areas of low concentration to areas of higher concentration. To move against a concentration gradient requires energy to overcome the inherent Brownian motion of the molecule. This always requires protein (enzyme) pumps. The word pump implies an active process that moves against a natural gradient or flow.
By far, the most commonly discussed pumps will be the ion pumps. There are two that you should become familiar with, as well as the resulting gradients.
- Sodium-Potassium ATPase (also known as the Na+/K+ pump).
- This helps to establish and maintain the Sodium and Potassium gradients of a cell.
- Sodium should be at high concentrations outside of the cell (extracellular)
- Potassium should be a high concentrations inside of the cell (intracellular)
- This combined gradient helps to establish the Resting Membrane Potential of many cells (an electrical charge across the membrane).
- Proton Pumps
- These pump systems help to establish and maintain a proton (hydrogen ion) gradient.
- In Eukaryotes, this will be found along the inner mitochondrial membrane.
- In Prokaryotes, this will be found along the cell membrane.
- This is a critical electrochemical gradient for cellular energy.
Commit the following phrase to memory:
When an ion moves down it's electrochemical gradient, across a membrane, work (kinetic energy) is done.
We will come back to this phrase throughout the semester.
Daily Challenge: Na+/K+ pump
Using diagrams and text, describe the operation of the Na+/K+ pump.
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