BI220 - Phospholipid Bilayer Structure and Function

phospholipids

• amphipathic

• organize into bilayers to avoid exposure of hydrophobic regions to hydrophilic environments

membranes

• separate internal environment from external environment

  • inability of substances to rapidly overcome polarities of bilayer

types of lipids

• phospholipids

• cholesterol

• glycolipids

phospholipids

• 75%

• form phospholipid bilayer

cholesterol

• 20%

• provide stability and fluidity with temp changes

glycolipids

• 5%

• carb head instead of polar head

• cell signaling and recognition

mosaic

• composed of lipids, carbs, and proteins

  • determine selective permeability, cell recognition, and flexibility

fluid-mosaic

• composed of lipids, carbs, and proteins that are constantly moving in 2D

  • laterally, rotate, flex

regulation of fluidity

• saturated vs unsaturated fats

• temp

• cholesterol

how do saturated vs unsaturated fats regulate fluidity

• saturated fats rigid

• unsaturated fats fluid

how does temp regulate fluidity

• high temp = high fluidity

how does cholesterol regulate fluidity

• fluid at low temps

  • can fit between tails

• rigid at high temp

  • hold set of membranes together

lipid rafts

• regions of PM w/ high concentrations of cholesterol

  • stay clustered together

  • protein receptors

integral proteins (chemical properties, isolate)

• inserted firmly in bilayer

  • nonpolar

  • transporters, enzymes, receptors

  • need detergent to isolate

peripheral protein (chemical properties, isolate)

• attached to surface of PM

  • polar

  • cell-cell junctions, anchors, one sided transport

  • don’t need anything to isolate

membrane protein functions

• transport

• signaling

• adhesion

• enzyme

• linking

• recognition

transport protein

• transport substances across PM

  • Na+/K+ pump

signaling

• receptors for signaling across membrane

  • G protein coupled receptors

adhesion

• attachment to cytoskeleton and ECM

  • integrals

enzyme

• enzymatic actvity

  • sucrase

linking

• linking cells to share intracellular fluid

  • cadherins

recognition

• cell-cell recognition

  • ligand channels

lipid types determine

• membrane fluidity, flexibility

• cell recognition

• cell signaling

• response to temp

protein types determine

• selective permeability

• cell recognition

selective permeability is permeable to

• hydrophobic, small polar molecules

selective permeability is impermeable to

• ions

• large hydrophilic molecules