The Plasma MembraneHonors Anatomy& Physiology

Plasma Membraneboundary between inside &

outside of cellflexible structuredynamic role in cellular activities

Plasma MembraneFluid Mosaic Model

resembles an ever-moving sea of fluid lipids that has large proteins bobbing along throughout the lipids

Cell Membrane: Lipid-Bilayer

Fluid Mosaic Model◦phospholipids

Membrane Lipids1. Phospholipids (~70% of

membrane)2. Cholesterol (20%)

◦ changes fluidity of membrane

3. Glycolipids (5%)◦ sugar molecule attached to a

lipid◦ outer membrane only

4. Lipid Rafts◦ control protein-protein

interactions in membrane

Membrane ProteinsIntegral Proteins

◦go all the way thru the membrane

◦channel proteins◦carrier proteins◦receptor proteins◦enzymes

Peripheral Proteins◦on inside or outside of membrane

◦+/- attached to integral proteins

Plasma Membrane

Glycocalyx “sugar-coating” on cell surfaceimportant in cell-cell recognition

Cell Junctions

3 factors binding cells together:1. glycoproteins

◦ sticky

2. membrane contours of 2 cells fit together

3. cell junctions form

Cell Junctions: Tight Jctsintegral

proteins in 2 adjacent cells fuse together◦ impermeable

jct◦ prevent

molecules moving thru ECF between cells

Cell Junctions: Desmosomes

anchoring jcts◦holds cells together in thickening

called a plaque

Cell Junctions: Gap Jctsallows 2 adjacent cells to pass

ions, small molecules important in cardiac muscle

◦allows synchronized contractions

Cell Junctions

Interstitial FluidECF from bloodwater, a.a. sugars, fatty acids,

vitamins, hormones, enzymes, neurotransmitters◦cells must take in what it requires

Membrane Transportplasma membrane is selectively

permeable2 ways substances can pass:

1. Passive Transport2. Active Transport

Passive Transport

1. Diffusion2. Facilitated Diffusion3. Osmosis

Diffusion molecules or ions move from hi

lo concentrations◦due to KE◦Factors that speed up diffusion:1. concentration gradient2. temperature3. size of particles

Diffusion lipid bilayer nonpolar so small

nonpolar molecules allowed to pass◦oxygen molecules◦carbon dioxide◦small, uncharged polar molecules water glycerol

Facilitated Diffusionpolar substances move across

membrane down concentration gradient using a protein

1. carrier-mediated integral proteins carry specific molecules ligand attaches to protein which changes

shape molecule enters cell

2. channel-mediated selective to specific ion or water

(aquaporins) leakage channels always open gated channels controlled by electrical or

chemical signals

Carrier-Mediated Facilitated Diffusion

Leakage Channel

Gated Channel

Osmosis diffusion of water thru selectively

permeable membrane1. simple diffusion thru membranesmall polar molecule that

“wiggles” thru nonpolar bilayer when membrane lipids randomly move

Aquaporins (leakage channels) unsaturated fatty acid tails & cholesterol leave tiny spaces

Isotonic Solutionssame concentration of

nonpenetrating solutes as found inside cells◦0.9% saline◦5% glucose◦body fluids

Hypertonic Solutionshigher concentration of

nonpenetrating solutes than inside cells

cells crenate (shrink)used for extreme edema (excess

water in extracellular spaces)

Hypotonic Solutionsmore dilute than inside cellscells take in water burst =

cytolysis◦(hemolysis if RBC)◦used in extremely dehydrated

patients

Active Transportrequires proteins that combine

specifically and reversibly w/transported substance

solutes move against their concentration gradient◦so cell must expend nrg

Active Transport ProcessesPumps

◦Primary Active Transport◦Secondary Active Transport

Vesicular Transport◦Endocytosis

Phagocytosis Pinocytosis

◦Receptor-Mediated Endocytosis◦Exocytosis

Primary Active Transporthydrolysis of ATP provides nrg by:

1. transferring its 3rd phosphate group to the protein pump

2. pump changes configuration (shape)

3. causing ligand to move across membrane

4. are specific (no pump in particular cell no transport)

Na+K+Pump[K+] inside cell 10x > outside cell[Na+] outside cell 10x > inside cellconcentration gradient necessary for

all cells to maintain normal fluid vol.◦leakage channels in membrane allow

both to diffuse slowly but continuously ◦diffuse according to electrochemical

gradientsantiporter: moves 2 substances in

opposite directions

http://www.siskiyous.edu/class/bio12b/SodPotassXchngPmp.swf

http://brookscole.cengage.com/chemistry_d/templates/student_resources/shared_resources/animations/ion_pump/ionpump.html

2◦ Active Transport1◦ pump indirectly drives 2◦

pump moving other solutesnrg stored in the electrochemical

gradient created from 1◦ pump used to drive 2◦ pump◦Na+ moves back into cell (leakage

channels) as symporter◦sugars

Vesicular Transportmove fluids made of large

particles & macromolecules ◦Endocytosis◦Exocytosis◦Transcytosis substances move across cell

organelle organelle

Phagocytosis: Cell Eating

Pinocytosis: Cell Drinking

Endocytosis: Receptor-Mediated

Exocytosis ejects substances out of cellstimulated by:

◦hormone binding to receptor◦change in membrane voltage

release of:◦hormones◦neurotransmitters◦mucus◦cell waste

Resting Membrane Potential

consequence of pumps, especially Na+/K+ pump, a difference in charge exists across membrane = voltage

in resting state all plasma membranes have resting membrane potential of

-50 to -100mV(-) sign indicates inside of cell (-) compared to outside

so we say all cells are polarized

Resting Membrane Potential

exists only at the membrane◦overall inside and outside neutral

Cell-EnvironmentInteractions

always involves plasma membrane

glycocalyx is key