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Cell Membrane

Medical Cell Biology

Components/character of a cell membrane Phospholipid bilayer, cholesterol, proteins. Asymmetric
Membrane lipids Phosphotidylcholine, phosphotidylserine, phosphotidylethanolamine, phosphotidylinositol, and sphingomyelin
Membrane lipids found in the outer leaflet Phosphotidylcholine and sphingomyelin
Membrane lipids found in the inner leaflet phosphotidylserine, phosphotidylethanolamine, and phosphotidylinositol
Which membrane lipid should never be in the outer leafleat Phosphotidylserien. Unless it is for RBC 120 days break down or for platelet aggregation
Glycolipids Made in the Golgi, carbohydrate that is EXCLUSIVELY attached on the outter leaflet, blood group antigen recognition
Cholesterol Help maintain structural integrity of plasma membrane at extrem temperature. Less cholesterol = more fluidity. More cholesterol = more rigid.
Lipid Turnover Remodelling or repairing damage from endocytosis, exocytosis, oxidative damage, ROS attacking polyunsaturated fatty acids.
Phospholipase A2 (PLA2) Hydrolyzes phospholipids into lysophospholipid (LPL). FA + Coenzyme A = FattyCoA. LPL + FattyCoA = New Phospholipid
PLA2 in arachidonic acid hydrolysis PLA2 hydrolysis phospholipids --> arachidonic acid. 1) Arachidonic acid --> 5-lipoxygenase --> Leukotrienes 2) Arachidonic acid --> cycloxygenase --> PGH2 --> Prostaglandins and thromboxanes
What inhibits the COX enzyme? aspirin
Phospholipase C PLC generates DAG for signal transduction. GPCR can activate PLC which then leads to the production of DAG and IP3
Flippase ATP dependent. Outer to inner (unity directional)
Scramblase ATP independent. Ca+2 activated. Always flip things from inside to outside. Brings PS on the outer surface
What is the consequence of a non functioning Ca+2 ATpase Cannot pump out excess Ca. Influx of Ca inside cell will stimulate scramblase. Scramblase will bring PS on the outer leaflet
Active scramblase + Flippase minimal PS exposure
Active scramblase + deactivated flippase Exposure of PS on outer surface In case of sickle cell anemia, PS should not be on the outer leaflet. This causes cells to stick together
Lipid Raft Region of cell membrane where lipids and proteins enriched. Decreased membrane cholesterol leads to melting of lipid raft
Lipids Cholesterol, sphingolipids, sphingomyelin and glycolipids
Integral Membrane Proteins Integral membrane proteins don't flip flop. They can either be single pass or multipass
Single pass integral membrane protein Membrane spanning region: hydrophobic. Regions in cytosol and outside cell: hydrophilic. Example glycophorin A
Multi-pass integral membrane proteins Includes transporters, ion channels. Membrane spanning regions may include polar or charged amino acids. Example Band 3
Peripheral Membrane Protein Associated through ionic interaction with an integral or another peripheral membrane protein
Diffusion Small, hydrophobic or hydrophilic molecules can diffuse through membrane according to their concentration gradient (N2, O2, EtOH, Urea)
Osmosis Water movement (hyperosmotic, hypoosmotic, iso-osmotic)
Aquaporins Used for transport of water, leading cause of cataract in children, Integral membrane proteins, Defects can lead to nephrogenic diabetes insipidus, congenital cataracts in children
Donnan Effect The presence of large molecules on one side balances the greater concentration of a certain ion on the other side. Na+ moves in, water follows, cell burst.
How is the Donnan Effect balanced? Na+/K+ATpase by pumping out 3 Na+ ions and take 2K+
Facilitated Transport Facilitated transport is required when molecules are too large.
GLUT Facilitated transporter. Used for glucose transport.Pri
2 types of Active Transport Primary and Secondary Active transport
Primary active transport Movement of molecules across a membrane against its concentration gradient. Need ATP
Secondary active transport Movement of molecule 1 across a membrane using free energy derived from transport of molecules 2 down the electrochemical gradient; co-transport
Primary Active Transport Na/K ATPase. Transport 3 Na+ ions out of cell and 2 K+ ions into cell uses 1 ATP.
Ouabain and digitalis inhibits Na/K ATPase pump. Increases [Na+] and [Ca2+]. Increases contractile activity
Symport Same direction. Example Na/Glucose (or amino acid) symport (SGLT)
Antiport Opposite direction. Example: Na/Ca
CFTR defect Accumulation of Cl- ions outside of cell. Sweat test will show elevated level of Cl-
Created by: jsabangan