Histology (Cell Surface)

outer membrane of a cell

membrane surrounding an organelle

membrane surrounding the nucleus

phospholipids
glycolipids
cholesterol

bile salts form micelles which surround the fat-soluble vitamins so that they can be absorbed by the intestines

phophatidylcholine
sphingomyelin
phosphatidylethanolamine
phosphatidylserine
phosphatidylinositol

located in both leaflets of the plasma membrane, cholesterol helps to maintain the structural integrity of the membrane

outer leaflet - phosphatidylcholine and sphingomyelin

inner leaflet - phosphatidylserine, phosphatidylinositol, phosphatidylethanolamine

key signalling molecules

it is flipped from the inner leaflet to the outer leaflet during apoptosis, allowing macrophages to recognize the cell and to phagocytose it

regions of plasma membrane enriched in choleterol, sphingolipids, and signalling proteins

give order to membrane, but float through the membrane

specialized type of lipid raft, invaginated into the cell membrane because of the protein caveolin

important for endocytosis (clathrin-independent) and signal transduction

protein icebergs in a lipid sea

peripheral - can be removed w/o dissolving lipid bilayer

integral - embedded in or covalently bound to lipid bilayer and cannot be removed without disrupting the plasma membrane

detergents

preferentially remain attached to P-face (protoplasmic face) of inner leaflet, rather than E-face of outer leaflet

many of the membrane proteins are bound to internal cytoskeleton

rotation around central axis
flexion of fatty acid chain
lateral movement through membrane
exchange leaflets (flip-flop)

facilitate the "flip-flop" of phospholipids from one leaflet to the other

increase in cholesterol integrated into membrane

protective membranes - myelin - more lipid than protein

functional membranes (transport, etc.) - mitochondrial membrane - more protein than lipid

outer leaflet

aka cell coat

high density of carbohydrate residues extending into extracellular space

participates in cell adhesion and recognition

passive transport in which a molecule moves down its concentration gradient

passive transport of large polar molecules or ions, down their concentration gradient, though with the aid of specific channels or transport proteins

highly folded transmembrane proteins that form small aqueous pores in the cell membrane

V-gated - open in response to changes in electrical potential across the plasma membrane

ligand-gated - open in response to the binding of a signaling molecule

pore size

charge interactions

transport across a cell membrane that requires no energy

moving ions or molecules across a cell membrane against their concentration gradient

defect in the cystic fibrosis gene, which encodes the chloride channel cystic fibrosis transmembrane conductance regulator (CFTR)

most common mutation results in lack of full folding and glycosylation, and resulting in degradation

release of materials by cells by fusion of intracellular granules with the plasma membrane

continuous secretion, so the vesicles are exocytosed immediately after being synthesized

episodic secretion, so the vesicles are stored in the cell until an extracellular signal activates the cell to secrete them

uptake of material by cells

pinocytosis
receptor-mediated endocytosis

fluid-phase endocytosis

(non-specific uptake of extracellular fluid into caveolin-coated vesicles)

specific uptake of a substance by a cell
1. ligand binds to receptor
2. ligand-receptor complexes gather into clathrin coated pit
3. clathrin-coated pit invaginates into a clathrin-coated vesicle
4. clathrin coat lost rapidly inside cell
5. clathrin coat, membrane, and receptor are recycled
6. ligand broken down and used by cell

uptake of cholesterol by cells via LDL receptor

uptake of iron by cells via transferrin receptor

uptake of microorganisms, other cells and/or foreign particles by a cell, involving extension of pseudopodia which wrap around targeted material

molecule released by a cell, binding to receptors on the same cell and inducing changes

IL-2 production by T-cells drives proliferation of the same T-cell which produces it

heat shock proteins are released from the intracellular receptor (in cytosol), the receptor dimerizes, and translocates to the nucleus, where it binds to a hormone response element, triggering DNA transcription

aka vitamin D receptor (VDR)

steroid hormone receptor which forms heterodimer with retinoid-X receptor, forming a transcription factor

phosphorylates/adds a phosphate group to a protein

causes conformational changes, which generally activates an enzyme

dephosphorylates/removes phosphate group from a protein

causes conformational changes which generally inactivates an enzyme

colorectal cancer

mutant Ras is hyperactive and drives gene expression, cell growth and cell differentiation

stimulation of TSH receptor by autoantibodies (which bind to receptor and trigger immune response, but also agonize the receptor)

drugs/molecules which bind to a receptor and mimic the effects of the normal ligand for that receptor

drugs/molecules which bind to a receptor but do not activate it, competitively inhibiting the action of normal ligands

e.g. propanolol

antagonists for the noradrenergic beta receptor in cardiac muscle, leading to lower blood pressure and lower arrhythmias in patients

powerful analgesic partial agonist of mu-opioid receptors (nociception receptors)

(much more potent than morphine)