Active transport
Active transport is when molecules move across a cell membrane from a lower concentration to a higher concentration. This takes energy, often from adenosine triphosphate (ATP). Active transport is done so cells get what they need, such as ions, glucose and amino acids.[1]
In general, molecules move from an area of higher concentration to an area of lower concentration. To get molecules into the cell against the concentration gradient, work must be done.[2] The work is done in special proteins which act as ports in the cell membrane. The imports must come through the ports: they cannot get through the bilipid layer of the cell membrane.
Types of ports
[change | change source]There are three main types of protein ports in cell membranes: [3]
- Uniporters: they use energy from ATP to pull molecules in.
- Symporters: they use the movement in of one molecule to pull in another molecule against gradient.
- Antiporters: one substance moves against its gradient, using energy from the second substance (mostly Na+, K+ or H+) moving down its gradient.
References
[change | change source]- ↑ "The importance of homeostasis". Science. BBC. Retrieved 15 December 2014.
- ↑ William K. Purves; et al, Life: the science of biology (Princeton, NJ: Recording for the Blind & Dyslexic, 2004), pp. 98–99.
- ↑ Bruce Alberts; et al, Molecular Biology of the Cell, 5th ed. (New York: Garland Science, 2008), pp. 619–631