topic 8 - the cell membrane

membrane form

double layer phospholipid; fluid mosaic model

membrane function

controls traffic into and out of the cell

selective permeability

A property of a plasma membrane that allows some substances to cross more easily than others; maintains integrity inside the cell

how many models are there of the plasma membrane?

4 models; in 1915, 1925, 1935, and 1972

1st plasma membrane model (1915)

made by Charles Overton; proposed that the membranes are made of lipids because lipids passed through (the membrane) easily

phospholipids

an amphipathic molecule; has a phosphate head and fatty acid tails

amphipathic molecule

a molecule with 2 sides: a hydrophilic & hydrophobic region

what is the phosphate head like?

it is negatively charged & hydrophilic

what is the fatty acid tail like?

it's made of nonpolar covalent bonds & is hydrophobic

2nd plasma membrane model (1925)

made by Gorter and Grendel; proposed a double layer (bilayer) of phospholipid. The outsides were philic and insides were phobic.

the sandwich model

the 3rd plasma membrane model made by Davson and Danielli in 1935; proposed that phospholipids may also be proteins since they don't actually adhere well to water

the fluid mosaic model

the 4th plasma membrane model made by Singer and Nicholson in 1972; proposed proteins floating in a sea of lipids but the proteins have to be amphipathic too

what does "fluid" mean in the fluid mosaic model?

the model shows that membranes can't be rigid, they should be "fluid" otherwise the cell wouldn't work

what does "mosaic" mean in the fluid mosaic model?

the model contains protein "tiles"

phospholipids (in FMM)

they sway back & forth. They are unsaturated in plant cells.

peripheral proteins (in FMM)

probably attached to the cytoskeleton or extracellular matrix (ECM); on edges

extracellular matrix

The substance in which animal tissue cells are embedded, consisting of protein and polysaccharides.

integral proteins (in FMM)

of several kinds: transmembrane, transport, channel, etc. They are proteins that are permanently embedded within the cell membrane. some proteins fully cross the cell membrane & others are partially in the hydrophobic section

Transmembrane (integral) proteins

cross the cell membrane & fully go through

Cholesterol

in animal cells, it prevents stiffening at low temperatures but it also helps prevent melting at high temperatures

carbohydrate tags

receptors that provide information on where a certain molecule was made to go

glycolipid

a lipid with one or more covalently attached carbohydrates

channel protein

a specialized protein that allows specific substances to enter or exit cells

transport protein

protein that moves substances or wastes through the plasma membrane