Plasma Membrane .pdf

Plasma Membrane Wednesday, September 13, 2023 8:19 AM Main idea: → The plasma membrane controls movement of everything that moves in and out PLASMA MEMBRANE → Also called the cell membrane → Surrounds every cell → Extremely thin bi layer - 2 layers of phospholipids ○ C...

Plasma Membrane Wednesday, September 13, 2023 8:19 AM Main idea: → The plasma membrane controls movement of everything that moves in and out PLASMA MEMBRANE → Also called the cell membrane → Surrounds every cell → Extremely thin bi layer - 2 layers of phospholipids ○ Composed of proteins and lipids (and some carbohydrates and cholesterol) → Separates the extracellular and intracellular compartments / fluids ( ECF / ICF ) Slide notes : → The plasma membrane controls movement of molecules into and out of cell (not only a mechanical barrier) → Active role in determining the composition of the cell by selectively permitting the movement of various molecules (Ions, nutrients, secretory and waste products, etc…) → Key in cell-to-cell environment communication STRUCTURE AND COMPOSITION: Slide notes: ○ The most abundant membrane lipids are phospholipids (PL) (and some cholesterol) ○ ≈ 1 billion PL moleucles are present in the plasma membrane of a typical human cell Picture description: ○ The middle keeps water out because the tails are hydrophobic Slide notes: ○ PL have a polar head and two nonpolar fatty acid chain tails Picture Description: ○ Each layer has many phospholipids that contain a head and a tail ○ The head - Composed of a phosphate group - Is negatively charged and polar there making it bond w water - Is hydrophilic ○ The tail ○ Uncharged and nonpolar ○ Hydrophobic = hates water, repels it More Slide Notes: → PL self assemble into a lipid bilayer = double layer of lipid molecules ○ Fluid (not rigid) : consistency more like cooking oil than a stick of butter. PL are constantly moving = twirl, vibrate, and move around within their half of the bilayer, exchanging places millions / sec → Cholesterol ○ Contributes to the fluidity and stability of the membrane ○ Intercalated in between the PL molecules Additional Notes: → Enzymes and the death of cells make the head and tail switch spots (they flip) FLUID MOSAIC MODEL → Most lipids, proteins and some carbohydrates → The Fluid Mosaic Model refers to membrane fluidity and the ever-changing mosaic pattern of the proteins embedded in the lipid bilayer → The fluidity of the lipid bilayer enables many membrane proteins to float freely like "icebergs" in moving "sea" of lipids ADDITIONAL NOTES ○ PL has abut 50 times more lipid molecules than Protein molecules. However proteins account for Nearly half of the membranes mass because they Are much larger than lipids ○ Different proteins result in different cell capabilities MEMBRANE PROTEINS → Channels ○ For small enough [≦ 0.8nm] water-soluble molecules, such as small ions); selective (e.g. Na+ channel) ○ Allows ions to pass through ○ Has certain channels that are ion specific → Carrier molecules ○ (transfer of specific substances; glucose has glut transporter) ○ For larger specific molecules → Docking-marker acceptors ○ For secretory vesicles and exocytosis process ○ When the cell wants to expel or release a substance it's put into a vesicle which has targeting protein that can match with a docking-marker acceptor that lets it pass through the membrane and be exported → Membrane- bound enzymes ○ Anchor on the membrane, can be on either side ○ Takes part in transmitting signals → Receptors ○ Can see growth hormones, immune signaling proteins, etc. ○ Can bind to molecules and facilitate the commination b/w the ECF and the cell → Cell adhesion molecules (CAMs) ○ Allows cells to adhere to each other → Peripheral proteins ○ Proteins that aren't spanning ○ They don't cross the membrane ○ Stay on their side of the membrane