6 Membrane Proteins & their Function
0. Are Membrane Proteins free to move about the membrane or are they fixed in
place? free to move about the cell
o what was the experiment that answered this question? fusing a mouse and
a human cell into a hybrid cell. Later, the mouse and human proteins were
mixed on the cell surface.
1. Adhesion proteins
o where are they in the membrane? embedded in the membrane but mostly
on either the outer cell surface or the inner cell surface
o what do they do? they either anchor the cell in position in the extracellular
matrix or they anchor something inside the cell.
2. Communication proteins
o are also called Gap Junctions
o where are they in the membrane? span the membrane
o what do they do with others like them? they hook up (connect) to other
gap junctions in a neighboring cell
o what do they form? large channels between the cell so that their cytoplasm
is connected
o what are they important in? chemical/electrical signaling
3. Receptor proteins
 embedded in membrane, receptor is on one side
 signal molecules (ie. hormones) bind to these proteins
 binding ... changes cell activities (growth hormone, cell get's ready to divide)
4. Recognition proteins
o on cell membrane's outer surface
o identify a cell as belonging to its host
o how body recognizes bacteria, virus, etc as non-self, immune defense
o important in blood typing (ABO), organ grafting
o help cells of a tissue type find and attach to one another
5. Passive transport proteins
o span membrane & form channels
o allow specific molecules to pass w/o expending E
o animals/plants have numerous to allow water
6. Active Transport proteins
o span membrane & form channels
o allow specific molecules to pass w expending E
o allow a molecule to move to an area of higher concentration
o H+ ion pump, requires ATP