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Lipids and Membranes

Biochemistry, Medicine, Phase 1

Components of plasma membrane structure hydrophobic regions, hydrophilic regions, proteins, glycoprotein, carbohydrate side chain
Carbohydrate side chain will usually face out into the extracellular space
Membrane composition varies according to cellular location
Carbohydrates only found in which membrane plasma membrane; 8%
1:1 protein protein:lipid ratio plasma membrane, out mitochondrial membrane
3:1 protein: lipid ratio inner mitochondrial membrane; nuclear membrane
Most common lipid is cell membrane phos/choline
Other lipids found in membranes (Varying degrees) phos/serin, spingomyel, cholesterol, others
Lipids insoluble in water, soluble in fat and organic solvents
Function of lipids energy stores (triacylglycerol), precursor for vitamins and hormones, bile acids (cholic acid), membrane structure (phospholipids)
Phospholipids essential and major component of all membranes;
Hydrophilic component of a phospholipid composed of polar head group (serine, choline, ethanolamine, inositol) attached to a backbone of glycerol through a phosphate group
Hydrophobic component of a phospholipid two fatty acyl side chains linked to the glycerol backbone via ester bonds
Amphipathic phospholipids f.e.g; both polar and nonpolar components
Common head groups found in phospholipids choline, serine, ethanolamine, inositol
Sphingomyelin lacks a glycerol backbone; component of neural membrane of myelin; polar head is choline attached to the phosphate group; phosphate group directly attaches to ceramide which is connected to a fatty acyl chain (only one)
Shingosine ceramide + fatty acyl chain
Glycerol backbone CH2, CH, CH2 (across), two O down which attach to the fatty acid chains
Each glycerophospholipid contains two fatty acids
Fatty acids can be fully saturated, mono-unsaturated and poly-unsaturated
Fully saturated no double bonds (number of carbon atoms in the fatty acid: number of double bonds)
Stearic acid 18:0; 18 carbon atoms in fatty acid, no double bonds, SFA
Palmitic acid 16:0; 16 carbon atoms in fatty acid, no double bonds, SFA
Myristic acid 14:0; 14 carbon atoms in fatty acid, no double bonds, SFA
Mono-unsaturated one double bond, MUSFA
Oleic acid 18:1; 18 carbon atoms; 1 double bond, MUSFA
Poly-unsaturated several double bonds
Arachidonic acid 20:4; 20 carbon atoms, 4 double bonds; PUSFA
Delta indicates position of double bonded in relation to the carboxyl group ; counting from the carboxyl terminal
Kink produced by a double bond in a fatty acid
Cholesterol hydroxyl group on cholesterol interacts with the polar head groups of the membrane phospholipids and sphingolipids; the bulky steroid and the hydrocarbon chain are embedded in the membrane, alongside the nonpolar fatty-acid chain of the other lipids.
Lipid bilayers are asymmetrical two halves of the bilayer have different membrane composition
Phospholipids facing extracellular environment phosphatidylcholine; sphingomyelin
Phospholipids facing intracellular environment phosphatidylerserine, phosphatidylethanolamine
Generation of phospholipids within the cell; requires an enzyme to get them in the right place in the membrane
Glycolipids are lipids with a carbohydrate attached
Fluidity the ease in which lipid molecules move about in the plane of bilayer - important in the regulation of membrane function (e.g. movement of proteins, signalling, exocytosis)
Regulation of fluidity fatty acids are crucial regulators of fluidity, determined by chain length and degree of saturation
Short chain fatty acids reduce the tendency of hydrocarbon chains to interact and hence increase fluidity
Kinks in unsaturated fatty acids result in less stable van der Waals interactions with other lipids and hence inrease fluidity
High cholesterol content restricts the random movement of polar heads, orders the lipid bilayer and decreases fluidity - rich in highly ordered regions of the membrane lipid rafts
Impaired fluidity can damage cells; increased cholesterol content of red blood cell membranes is associated with severe liver diseases e.g. Cirrhosis
Abnormal cholesterol levels when content of red blood cells is increased by 20-60% above normal, leading to decreased fluidity; alters cell shapes; impairs oxygen transport, destruction of red blood cells and anaemia
Structural cell membrane proteins cell-cell contact, cytoskeletal organisation
Receptor cell membrane proteins signal transduction and recognition
Ion channel cell membrane proteins maintenance of ion gradients, transmission
Transporter cell membrane proteins important and export substances
Enzyme cell membrane proteins catalysis
Actin, spectrin, ankyrin structural cell membrane proteins
Insulin receptor, glucagon receptor receptor cell membrane proteins
Acetylcholine (nicotine), GABAa ion channel cell membrane proteins
Glucose and glutamate transporters transporter cell membrane proteins
Adenylyl cyclase enzyme membrane proteins
Integral (intrinsic) proteins embedded in lipid bilayer, most span the entire bilayer; transmembrane spanning domains are either alpha helices or beta sheets; can span the membrane completely or not properly but are embedded within the membrane; channel or transporter
Anchored proteins anchored to membrane by covalently bound fatty acids
Peripheral (extrinsic) proteins attach to membrane surface by ionic interactions with integral proteins or with polar head group of phospholipids
Integral membrane protein (2)
Anchored membrane proteins (2) not deeply embedded in the bilayer by covalently linked to fatty acid chains (e.g. myristic or palmitic acid) or on the cell surface to a glycolipid
Alkaline phosphate enzyme; example of a glycolipid anchored protein
RAS example of fatty acyl anchored protein; signalling protein; relays information from the cell membrane
Peripheral proteins (2) attach to the membrane surface by interactions with other membrane proeins or with the polar head group of phospholipids
Spectrin important structural protein; on the cytoplasmic surface of erythrocytes; interacts with other proteins such as ankyrin
Phospholipase A2 peripheral protein; binds to bilayer to cleave fatty acids from phospholipids
Sites of action of phospholipases polar head (choline, ethanolomaine, myo-inositol) from phosphate group (PLD); phosphate group from glycerol backbone (PLC); remove the fatty acids (PLA1 - usually saturated), (PLA2, usually unsaturated)
High salt, urea treatment removes peripheral proteins from the bilayer
Detergent (protein solution) removes peripheral, anchored and integral proteins of the bilayer
Phospholipase removes peripheral and anchored proteins of the bilayer; peripheral proteins (PLA, 2)
Detergents are preferred method over organic solvents; like soaps; similar structure of phospholipids with a hydrophilic head and a hydrophobic tail; detergent monomers form detergent polymer micelles
Micelles polymer of detergent monomers
Micelles + membrane proteins results in water-soluble-lipid-detergent complex and water-soluble-lipid-detergent micelles; removing detergent and adding phospholipids back to proteins allows you to study your protein of interest and its function
Created by: emmaallde



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