The Plasma Membrane Honors Anatomy Physiology Plasma Membrane

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 Phospholipids (~70% of membrane) 2. Cholesterol (20%) 1. ◦ changes fluidity of membrane Glycolipids (5%) 3. ◦ ◦ sugar molecule attached to a lipid outer membrane only Lipid Rafts 4. ◦ 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 membrane contours of 2 cells fit together 3. cell junctions form 2.

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 Diffusion 2. Facilitated Diffusion 3. Osmosis 1.

Diffusion or ions move from hi lo concentrations �molecules ◦ 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 10 x > outside cell �[Na+] outside cell 10 x > 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: directions moves 2 substances in opposite

http: //brookscole. cengage. com/chemistry_ d/templates/student_resources/shared_res ources/animations/ion_pump/ionpump. html http: //www. siskiyous. edu/class/bio 12 b/Sod Potass. Xchng. Pmp. swf

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

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 -100 m. V (-) 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