Cell Membrane and Transport Flashcards
interstitial fluid
ECF that surrounds cells
functions of membrane proteins
1) transport
2) receptors for signal transduction
3) attachment to cytoskeleton and extracellular matrix
4) enzymatic activity
5) intercellular joining
6) cell-cell recognition
Tight junctions
neuro (BBB)
prevent fluids and most molecules from moving b/w cells
Gap junctions
cardiac
transmembrane proteins form pores that allow small molecules to pass from cell to cell
Determinants of passive permeability
lipid solubility, channels of appropriate size, carrier proteins
Simple Diffusion
non-polar lipid soluble substances diffuse directly through phospholipid bilayer
Facilitated Diffusion
(passive) certain lipophobic molecules (glucose, amino acids, ions) use carrier proteins or channel proteins
Two types of channel proteins
- leakage channels (K) always open
- gated channels (Na) controlled by chemical/electrical signals
Osmosis
movement of water across SPM, either through lipid bilayer or through aquaporins; water concentration determined by solute concentration
Osmolarity
measure of total concentration of solute particles
Two types of active processes
active transport
vesicular transport
(both use ATP to move solutes across membrane)
Active Transport
requires carrier proteins- moves solutes against gradient
Primary active transport
energy from hydrolysis of ATP causes shape change in transport protein so that bound ions are pumped across membrane (Na/K pump)
Secondary Active Transport
depends on an ion gradient created by primary active transport- energy stored in ionic gradients used indirectly to drive transport of other solutes
Cotransport
- secondary active transport
- symport- 2 substances transported in same direction
- antiport- 2 substances transported in opp direction
Vesicular Transport
transport of large particles, macromolecules, and fluids across plasma membranes- requires ATP
Functions of Vesicular Transport
- exocytosis- out of cell
- endocytosis- into cell
- transcytosis- into, across, then out of cell
- substance (vesicular) trafficking- transport from one area/organelle to another
Examples of exocytosis
hormone secretion, NT release, mucus secretion, ejection of wastes
Membrane Potential
Separation of opposite charged particles across membrane (measured as voltage)
Generation/maintenance of RMP
1) Na/K pump continuously ejects Na from cell and carries K back in
2) some K leaks out constantly
3) membrane interior becomes neg because of large anions trapped inside cell
4) electrochemical gradient attracts K into cell
5) RMP est. at point where gradient balances K gradient
6) steady state maintained b/c rate of active transport = to and depends on rate of Na diffusion into cell
Roles of Membrane Receptors
- contact signaling
- chemical signaling
- G protein linked receptors
contact signaling
touching/recognition of cells; normal development and immunity
chemical signaling
interaction b/w receptors and ligands to alter activity of cell proteins
G protein linked receptors
ligand binding activates G protein, affecting ion channel or enzyme or causing release of internal second messenger (like cAMP)
