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WEEK 6:
Cell Membrane:
| Question | Answer |
|---|---|
| glycocalyx | layer of carbohydrates attached to glycoproteins + glycolipids |
| what does the glycocalyx consist of | oligosaccharides on surface with proteins + lipids extending into aqueous medium |
| how much weight does the glycocalyx contribute to the plasma membrane | 10% |
| function of glycocalyx | protects cell from digestion, restricts uptake of hydrophobic compounds, regulates cell recognition |
| physical properties of membrane | flexible, self-sealing, selectively permeable |
| membrane is involved in what processes | exocytosis, endocytosis, cell division |
| how do membranes vary by cell physiology | different energy use, protein production + biomolecule export |
| compare the membranes in liver hepatocyte and pancreatic exocrine cells | pancreatic exocrine cells have smaller mitochondria + SER membranes |
| describe selective permeability | lipid bilayer has hydrophobic interior so ion movement restricted meaning it only travels via concentration gradients through channels |
| describe ion levels in blood plasma, interstitial fluid and intracellular fluid | K+ high inside (intracellular fluid), Na+ low inside and high inside |
| what is the pKa and charge of fatty acids in membrane lipid | pKa 4.8 with a negative charge |
| three principal lipids components in bilayer | phosphoglycerides (phospholipids) sphingolipids (mostly glycolipids containing carbohydrate), cholesterol (a sterol) |
| most abundant phospholipid in membranes | phosphatidylcholine |
| sphingolipids | contain sphingosine moiety including fatty amine chain, mostly glycolipids, common in neuronal membranes eg myelin sheaths |
| cholesterol | a sterol (lipid with 4 fused hydrocarbon rings), more rigid than other membrane lipids, made of ≥10% total lipid in plasma membrane, maintain membrane fluidity, plants does not have it only has phytosterols |
| why is a vegan diet cholesterol free | plants do not have cholesterol, only have phytosterols |
| sterol meaning | lipid with 4 fused hydrocarbon rings |
| in an aqueous solution, what do amphipathic lipids + detergents form | micelles |
| when is the bilayer formation preferred | if cross-sectional areas of head group and acyl side chains are similar |
| what happens if edges in lipid bilayer are exposed | vesicles form |
| compare the outer and inner leaflet of the lipid bilayer | outer has more phosphatidylcholine and inner has more phosphatidyl serine |
| lipids rafts | formed by sphingolipids + cholesterol, important in signalling |
| describe movement within leaflets and movement between leaflets | rapid within leaflets but slow between leaflets |
| what transporters help maintain membrane asymmetry | flippase, floppase and scramblase |
| flippase | selectively moves lipids to cytoplasmic side of membrane (outer leaflet -> inner leaflet) |
| floppase | selectively moves lipids to outside (inner -> outer leaflet) |
| scramblase | moves lipids in both directions for equilibrium |
| integral membrane proteins | contain transmembrane domains (stretch throughout), can have hydrophilic domains poking into extracellular and/or cytoplasmic spaces |
| peripheral membrane proteins | on lipid bilayer surface |
| lipid anchored proteins | bound to inner or outer membrane surface |
| difference between transporters and channels | transporters need energy but channels do not |
| how are membrane proteins important for attachment | attachment to cytoskeleton + ECM |
| GPCR in words | G protein coupled receptors |
| GPCR function | cell surface receptors that respond to external signals |
| GPCR composition | seven transmembrane domains |
| how do GPCRs work | binds to extracellular substances + transmits signals to G protein to activate it |
| G proteins | specialised proteins with ability to bind nucleotides GTP and GDP |
| what happens to activated G protein in GPCR sequence | triggers production of second messengers |
| what happens to second messengers in GPCR sequence | triggers changes in metabolism / gene expression |
| describe the whole sequence that GPCRs cause | (1- GPCRs bind to extracellular substances + send signals, activating G protein) (3- activated G protein releases GDP + binds to GTP triggering production of second messengers) (4- second messengers trigger changes in metabolism/gene expression) |
| examples of GPCRs | adrenoreceptors, muscarinic acetylcholine receptors + opioid receptors |
| examples of GPCR drugs | angiotensin receptor 1 blockers (losartan), H2 histamine receptor antagonist (cimetidine), Beta blockers (labetalol), epinephrine/adrenaline, opioid agonist (morphine) |
| how does angiotensin receptor 1 blockers (losartan) work as a GPCR drug | lower blood pressure |
| how does H2 histamine receptor antagonist (cimetidine) work as a GPCR drug | decrease stomach acid production |
| how does beta blockers (labetalol) work as a GPCR drug | blocks action of epinephrine + lower blood pressure |
| how does epinephrine/adrenaline work as a GPCR drug | target adrenergic receptors to control hypersensitivity reactions, bleeding, asthma + blood pressure |
| membrane proteins | integral, peripheral, lipid-anchored |
Created by:
kablooey
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