Membrane physiology Flashcards
Functions of the cell membrane
- defines the cell boundary (cells have varied shapes)
- encloses the cell’s organelles
- creates an internal environment to promote normal cell function, separate from the outside of the cell
Structure of the cell membrane
Phospholipid bilayer, composed of individual ampipathic units with a hydrophilic phosphate head and two hydrophobic fatty acid tails.
Resting membrane potential
Concentration gradients of charge-carrying particles inside and outside the cell give rise to a standing electrochemical gradient between the intra- and extra- cellular compartments.
Electrically excitable tissues
Able to momentarily discharge the standing electrical potential between the intra- and extra- cellular compartments. These include nerve and muscle cells.
How do cells create an intracellular compartment?
The cell membrane is selectively permeable to certain particles:
-ions may cross
-proteins may not cross
This is due to their size, electrical charge and specialised transport systems.
Transport systems
- transport ATPases (ion pumps)
- ion channels (selective/non-selective, leak channels)
Ion channels
- transmembrane spanning proteins, embedded within the full thickness of the CM
- have a water-filled central pore linking the intra- and extra-cellular compartments
- facilitate the passive movement of ions across the CM, in either direction
- may be selective or not
Specificity of ion channels
Each species of ion channel is unique in:
- which ions it conducts
- how the conductance of ions is governed
- gating mechanisms
Examples of ion channels
- voltage-gated ion channels
- ligand-gated ion channels
- mechanically gated ion channels
- non-gated ion channels
- leak channels
Ion pumps
- carrier proteins lodged within the CM
- function to maintain the RMP, requiring energy from ATP
- some are known as ion exchange pumps
