Lec 9/11 Flashcards
phospholipid structure
- polar head on surface, hydiphilic
- Fatty acyl tails inward, hydrophobic, form weak noncovalent bonds
- amphipathic(lipophilic/hydrophobic and hydrophilic)
unit membrane
- inner leaflet(inner surface Protoplasmic or P-face)
- outer leaflet(outer surface Ectoplasmic or E-face)
- 1:1 phospholipid to protein ratio
what are proteins on inner leaflet?
- phosphatidylserine(PS)
- phosphatidylethanolamine(PE)
what are proteins on outer leaflet?
- phosphatidylcholine(PC)
- phosphatidylglycerol(PG)
what is apoptosis?
- programmed cell death
- stimulus or signal to undergo programmed cell death (DNA fragmentation~180bp, followed by morphological changes to cell/membranes)
signs of apoptosis
cell shrinkage, fragmentation, engulfment/degradation, no inflammation, limited tissue damage
signs of necrosis
cell swelling, organelle rupture, membrane rupture, tissue damage, inflammation
what happen in a healthy cell
PS asymmetry, active “flippase” process, slight negative charge
what happen in an apoptosis cell?
PS asymmetry lost, lippase activity lower, PS externalized–> “eat me” signal
annexin assay
- protein binds to - charged phospholipid (PS)
- protein is couples to fluorophore (fluorescent)
- fluorescence can be visualized using microscopy
- apoptotic cells will be labled and glow or fluorescent
EX of amphipathic molecules
- phospholipids(fatty acyl tails increase membrane fluidity)
- glycolipids
- cholesterol(decreases membrane fluidity)
protein membrane components
- integral/transmembrane proteins (span membrane, ion channel, transport protein), multipass(signaling), more on P-face
- periferal proteins(mainly cytoplasmic face)
fluid mosaic model
- come mobility of integral proteins
- limited in polarized cells(apical, basolateral)-related to cellular function
glycocalyx-cell coat
- up to 50nm thick
- stains w/ lectins, Alcain blue (Ingrain blue)or ruthenium red
glycocalyx-carbohydrate chains
may be linked to transmembrane proteins, phospholipids
glycocalyxextracellular matrix(ECM)
may be constituent
glycocalyx-function
protect cell(physical or chemical insults)
how do nonpolar O2, uncharged polarH2O move acrsoss membrane?
- freely along [] gradients
- simple diffusion(passive diffusion)
how do ions and small molecules move across membrane?
- facilitated diffusion(passive diffusion)
- along [] gradients
2 types of membrane transport proteins(facilitate transfer of hydrophilic molecules)
- channel proteins:gated, move ions
- carrier proteins: move small proteins, molecules
channel proteins
- hydrophilic pores or ion channels(>100 types, gated, few are ungated)
- ion channel(hydrophobic aa face periphery, towards fatty acyl tails) and hydrophilic aa face inwards, toward inner channel surface
voltage-gated channels
- in ‘‘closed” position
- closed position is more stable(refractory period is milisec, gate cant be reopened)
- move to open position(Na+ channels, depolarization/transmission of nerve impulse)
Ligand-gated channels
*Ion-channel linked receptors
- binding of ligand triggers opening of channel
- remains open until ligand dissociates
Ligand-gated channel
*Neurotransmitter-gated channels
post-synaptic neuron
Ligand-gated channel
*Nucleotide-gated channels
- cAMP in olfactory receptors
- cGMP in retinal receptors
mechanically-gated channel
- stereocilia(projections) in tectorial membrane
- sounds create movement of basilar membrane
- stereoilia bend
- triggers ion channel opening
- depolariztion and nerve transmission
- nerve impulse translates sound
G-protein-gated ion channel
* what is G-protein complex?
- heterotrimeric GTP-binding protein
- 7 helix transmembrane, intra-, extracellular domains
G-protein-gated ion channe
* how do extracellular ligand changes conformation?
- GTP replaces GDP activating intracellular signaling
- activated protein interacts to open ion channel
ungated channel
- K+ leak channel
- creates voltage(potential) across membrane
what is aquaporins?
- impermeable to protons
- involved in proper kidney function, clearance
- AqpZ: passage of water
- GlpF: passage of glycerol
carrier proteins
- bind molecules or ions on both sides
- extra & intracellular face
- involved reversible conformation changes
carrier proteins-Uniport
- single molecule moving one way
- GLUT1 uniport carrier-faciliated transport
carrier proteins-symport
- 2 molecules moving one way
- SGLT(sodium-glucose linked transport) in nephron, renal glucose reabsorption, small intestine, oral rehydration therapy
carrier proteins-antiport
- 2 molecules moving opposite
- in oral and pharyngeal cancers
- importTryptophan (biosynthesis and metabolism substrate)
- export Kynurenine(down regulation of CD8 or Tcell)
what is EX of primary active transport?
- Na-K pump(coupled antiport carrier protein)
- require ATP (maintain >K inside, >Na outside)
Na-K pump
- 3 Na bind inside, ATP is hydrolyzed, ATPase is phosphorylated by phosphate, phosphorylation–>conformation change–> Na is transported outside
- 2K bind outside-> dephosphorylationof ATPase-> protein return to old conformation->K is transported inside
secondary active transport
- gradient driven
- can be symport or antiport
- K and glucose bind outside face of carrier protein->shape change->transfer and release into cytoplasm
types of cell surface receptors
- ion-channel linked receptors
- enzyme-linked receptors
- G-protein-linked receptors
