A&P Chapter 3 Membrane Proteins and Transport

Function of membrane proteins:

allow cell communication, make up half the mass of plasma membrane, have specialized membrane functions, some float freely; some are tethered

Two types of membrane proteins:

Integral proteins and peripheral proteins

Passive transport requires

Three types of passive transport:

simple diffusion, facilitated diffusion, and osmosis

Define diffusion:

natural movement of molecules from areas of high concentration to areas of low concentration

Speed of diffusion is influenced by 3 factors:

concentration, molecular size, and temperature

How does concentration influence speed of diffusion?

greater the difference of concentration, the faster diffusion occurs

How does molecular size influence speed of diffusion?

smaller molecules diffuse faster

How does temperature influence speed of diffusion?

higher temps increase kinetic energy

Equilibrium is reached when:

there is no net movement of molecules in one direction only

Simple diffusion

molecules that are able to passively diffuse through membrane

Facilitated diffusion

larger or non lipid soluble or polar molecules can cross membrane, but only with assistance of carrier molecules

Osmosis

movement of solvent(usually water), not molecules

Examples of nonpolar lipid-soluble(hydrophobic) substances:

oxygen, carbon dioxide, steroid hormones, and fatty acids

Examples of hydrophobic molecules:

glucose, amino acids, and ions

Carrier-mediated facilitated diffusion

substances bind to protein carriers

Channel-mediated facilitated diffusion

substances move through water-filled channels

Two types of channels (facilitated diffusion):

leakage and gated channels

Leakage channels

always open

Gated channels

controlled by chemical or electrical signals

Water diffuses through:

aquaporins

Define osmolarity

measures the concentration of the total number of solute particles in solvent

Define tonicity

ability of a solution to change the shape or tone of cells by altering the cells internal water volume

Isotonic solution

same osmolarity as inside the cell; volume remains unchanged

Hypertonic solution

higher osmolarity than inside the cell; water flows out of cell resulting in SHRINKING

Hypotonic solution

lower osmolarity than inside the cell; water flow into the cell resulting in SWELLING