The Plasma Membrane Honors Anatomy& Physiology

Plasma Membrane boundary between inside & outside of cell flexible structure dynamic role in cellular activities

Plasma Membrane Fluid 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 Lipids 1. 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 Proteins Integral 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 surface important 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 Jcts integral 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 Jcts allows 2 adjacent cells to pass ions, small molecules important in cardiac muscle ◦ allows synchronized contractions

Cell Junctions

Interstitial Fluid ECF from blood water, a.a. sugars, fatty acids, vitamins, hormones, enzymes, neurotransmitters ◦ cells must take in what it requires

Membrane Transport plasma membrane is selectively permeable 2 ways substances can pass: 1.Passive Transport 2.Active Transport

Passive Transport 1. Diffusion 2. Facilitated Diffusion 3. Osmosis

Diffusion molecules or ions move from hi  lo concentrations ◦ due to KE ◦ Factors that speed up diffusion: 1.concentration gradient 2.temperature 3.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 Diffusion polar 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 membrane 1. simple diffusion thru membrane small polar molecule that “wiggles” thru nonpolar bilayer when membrane lipids randomly move Aquaporins (leakage channels) unsaturated fatty acid tails & cholesterol leave tiny spaces

Isotonic Solutions same concentration of nonpenetrating solutes as found inside cells ◦ 0.9% saline ◦ 5% glucose ◦ body fluids

Hypertonic Solutions higher concentration of nonpenetrating solutes than inside cells cells crenate (shrink) used for extreme edema (excess water in extracellular spaces)

Hypotonic Solutions more dilute than inside cells cells take in water  burst = cytolysis ◦ (hemolysis if RBC) ◦ used in extremely dehydrated patients

Active Transport requires proteins that combine specifically and reversibly w/transported substance solutes move against their concentration gradient ◦ so cell must expend nrg

Active Transport Processes Pumps ◦ Primary Active Transport ◦ Secondary Active Transport Vesicular Transport ◦ Endocytosis  Phagocytosis  Pinocytosis ◦ Receptor-Mediated Endocytosis ◦ Exocytosis

Primary Active Transport hydrolysis of ATP provides nrg by: 1.transferring its 3 rd 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 cell concentration 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 gradients antiporter: moves 2 substances in opposite directions

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2 ◦ Active Transport 1 ◦ pump indirectly drives 2◦ pump moving other solutes nrg 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 Transport move 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 cell stimulated 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-Environment Interactions always involves plasma membrane glycocalyx is key