Membrane physiology

Question 1

Functions of the cell membrane

Answer 1

• 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

Question 2

Structure of the cell membrane

Answer 2

Phospholipid bilayer, composed of individual ampipathic units with a hydrophilic phosphate head and two hydrophobic fatty acid tails.

Question 3

Resting membrane potential

Answer 3

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.

Question 4

Electrically excitable tissues

Answer 4

Able to momentarily discharge the standing electrical potential between the intra- and extra- cellular compartments. These include nerve and muscle cells.

Question 5

How do cells create an intracellular compartment?

Answer 5

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.

Question 6

Transport systems

Answer 6

• transport ATPases (ion pumps)

- ion channels (selective/non-selective, leak channels)

Question 7

Ion channels

Answer 7

• 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

Question 8

Specificity of ion channels

Answer 8

Each species of ion channel is unique in:

• which ions it conducts
• how the conductance of ions is governed
• gating mechanisms

Question 9

Examples of ion channels

Answer 9

• voltage-gated ion channels
• ligand-gated ion channels
• mechanically gated ion channels
• non-gated ion channels
• leak channels

Question 10

Ion pumps

Answer 10

• carrier proteins lodged within the CM
• function to maintain the RMP, requiring energy from ATP
• some are known as ion exchange pumps