1. Department of Health, Nutrition, and Exercise Sciences
Chapter 3: Cells
Plasma membrane: structure
Plasma membrane: transport
Resting membrane potential
Cell-environment interactions
Cytoplasm
Nucleus
Cell growth & reproduction
Extracellular materials, developmental aspects
Department of Health, Nutrition, and Exercise Sciences

2. Resting membrane potential
All living cells at rest
Voltage inside is negative relative to outside
Ranges from –50 to –100 mV in different cells
Results from separation of oppositely charged particles (ions) across the membrane
A form of stored (i.e. potential) energy
Energy comes from active transport of ions (mainly pumping Na+ out of cells and K+ into cells)
Human adipocyte.
Yeh & Shi (2010), WIREs Nanomed Nanobiotechnol 2: 176–188.
Department of Health, Nutrition, and Exercise Sciences

3. Generation and maintenance of resting membane potential
Na+-K+ pump continuously pumps Na+ out, K+ in
Resting membrane virtually impermeable to Na+, slightly permeable to K+
Some K+ continually diffuses down its concentration gradient, out of cell, through K+ channels
Membrane interior becomes negative (relative to exterior) because anions can’t follow the K+ out: Vin<0

4. Generation and maintenance of resting membrane potential
Concentration gradient (chemical force) pushes K+ out. Negative intracellular voltage (electrical force) pulls K+ in. Net force is the electrochemical gradient.
When intracellular voltage is negative enough that electrical and chemical forces on K are (approximately) balanced, there is hardly any net force on K+, and that is the RMP.
Steady state is maintained because active transport of Na+ out and K+ in is equal and opposite to the residual leakage of Na+ in and K+ out.

5. Generation and maintenance of R.M.P.
K+ diffuses “down” its steep concentration gradient (out of cell) via leakage channels. Loss of K+ results in a net negative charge, and therefore negative voltage, inside cell. 1
Extracellular fluid
K+ also moves into cell because it is attracted to negative charge inside cell. 2
A stable negative membrane potential (-50 to -100 mV) is established when K+ movement out of cell equals K+ movement into cell. At this point, chemical concentration gradient for K+ exit is equal* & opposite to electrical gradient for K+ entry. 3
Potassium
leakage
channels
*Not exactly equal. Actual RMP is slightly more + than the voltage that would put K+ at equilibrium, so there is a small residual outflow of K+. This is counteracted by the Na-K pump.
Protein anion (unable to
follow K+ through the
membrane)
Cytoplasm
Figure 3.15

6. Involves glycoproteins and proteins of glycocalyx
Cell-Environment Interactions: How a cell connects to its surroundings, both literally and figuratively
Involves glycoproteins and proteins of glycocalyx
Cell adhesion molecules (CAMs)
Membrane receptors

7. Roles of Cell Adhesion Molecules
Anchor cells to extracellular matrix or to each other
Assist in movement of cells past one another
CAMs of blood vessel lining attract white blood cells to injured or infected areas
Stimulate synthesis or degradation of adhesive membrane junctions
Transmit intracellular signals to direct cell migration, proliferation, and specialization

8. Roles of Membrane Receptors
Contact signaling
touching and recognition of cells
receptors on one or both cells recognize proteins/glycoproteins on other cell’s surface
regulates development, growth, immunity, etc.
Chemical signaling
receptor recognizes chemical (ligand*) released by another cell
neurotransmitters, hormones, etc.
G protein–linked receptors
important class of membrane receptor proteins for chemical signaling
receptor activation turns G protein on or off
change in G protein causes change in intracellular concentration of a second messenger such as Ca or cyclic AMP (cAMP)
* Ligand = molecule that binds to a receptor

9. G Protein
relay between extracellular first messenger and intracellular second messenger