Bich 410 1st Edition Exam 3 Study Guide I Lipids A Function i Lipids in the form of a bilayer are essential components of biological membranes ii Lipids containing hydrocarbon side chains serve as energy stores iii Many intra and intercellular signaling events involve lipid molecules iv Lipid structure variable multiple functions possible B Fatty Acids i Fatty acids are carboxylic acids with long chain hydrocarbon side groups and hydrophilic head groups ii Fatty acids can form micelles and take part in bilayer structure formation but usually occur in esterified forms and serve as major components of other various lipids iii Saturated no double bonds unsaturated cis double bonds iv The degree of saturation is important as it impacts the ability of fatty acids to aggregate 1 The presence of double bonds introduces kinks in the tails preventing the efficient packing of fatty acids v Double bonds decreases the melting point vi Make sure you have the table of common fatty acids memorized common name number of carbons how many double bonds if any and where they occur C Triacylglycerols i fatty acid triesters of glycerol ii non polar water insoluble and the major energy reservoirs in animals iii storage insulation and energy iv they associate and localize to a specific type of cell known as adipocytes or fat cells D Glycerophospholipids i addition of the phospho alcohol head group in place of an esterified fatty acid side chain introduces a polar functional group ii The presence of this polar group shifts the molecule from being highly hydrophobic to be being amphipathic making it highly suitable for function within a membrane where the hydrophobic portion is buried in the interior of the membrane and the hydrophilic headgroup becomes solvent exposed iii Know how to name these know the different head groups E Sphingolipids These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute i II The basic building block is a ceramide a sphingosine with a fatty acid joined with an amide linkage ii Different head groups iii Play a role in the CNS F Sphingomyelins i glycerophospholipid due to the head group being phosphocholine ii They possess the sphingosine backbone and the amide linked fatty acid which forms the ceramide iii Form the myelin sheath in neurons G Cerebrosides i Glycolipid ii Headgroup is a single sugar iii Found in animal muscle and nerve cells H Steroids i Cholesterol ii Four fused nonplanar rings Membranes A Why form membranes i Water prefers polar interactions ii Water prefers to self associate through H bonds iii The hydrophobic effect promotes self association of lipids in water to maximize entropy B Composition i Membranes that carry out fewer such functions such as myelin sheaths are richer in lipid ii Membranes that carry out many enzyme catalyzed reactions and transport activities are richer in protein C Structure i Lipids form ordered structures spontaneously in water ii Very few lipids exists as monomers iii Micelles bury the nonpolar tails in the center of a spherical structure iv The amphipathic molecules that form micelles are each characterized by a critical micelle concentration CMC D Fluid Mosaic Model i The phospholipid bilayer is a fluid matrix ii The bilayer is a two dimensional solvent iii Lipids and proteins can undergo rotational and lateral movement iv Peripheral and integral proteins E Peripheral Proteins i not strongly bound to the membrane ii They may form ionic interactions and H bonds with polar lipid headgroups or with other proteins iii Or they may interact with the nonpolar membrane core by inserting a hydrophobic loop or an amphiphilic helix iv can be dissociated with mild detergent treatment or with high salt concentrations F Integral Proteins i strongly embedded in the bilayer ii They can only be removed from the membrane by denaturing the membrane organic solvents or strong detergents iii Often are transmembrane iv Surprising diversity in integral proteins v in all cases the portions of the protein in contact with the nonpolar core of the lipid bilayer are dominated by helices and sheets G Amino Acids i The sequence of a transmembrane protein is adapted to the transition from water to the hydrophobic core and then to water again ii Hydrophobic amino acids are found most often in the hydrocarbon interior iii Charged and polar residues occur commonly at the lipid water interface iv Trp His and Tyr are mixtures of polar and nonpolar parts They are found often at the lipid water interface v Arg Asp Asn Gln Glu Lys Pro more unfavorable in center vi Ala Gly Ile Leu Met Phe Val more favorable in center vii His Tyr Trp favorable at membrane water interfaces H Porins i pore forming proteins ii Most arrange in membrane as trimers iii High homology between various porins I Why Beta sheets for membrane proteins i Genetic economy need less information ii Alpha helix requires 21 25 residues per transmembrane strand iii Beta strand requires only 9 11 residues per transmembrane strand iv With beta strands a certain amount of genetic material can make more trans membrane segments J Lipid Anchored proteins i Amide Linked Myristoyl Anchors 1 The lipid anchor is always myristic acid 2 It is always N terminal 3 It is always linked to a Gly residue ii Thioester linked and Acyl Anchors 1 A broader specificity for lipids myristate palmitate stearate oleate all found 2 Broader specificity for amino acid links Cys Ser Thr are all found iii Thioether linked Prenyl Anchors 1 Prenylation refers to linking of isoprene based groups 2 Isoprene groups include farnesyl and geranylgeranyl groups iv Glycosyl Phosphatidylinositol Anchors 1 GPI anchors are more elaborate than others 2 Always attached to a C terminal residue 3 Ethanolamine link to an oligosaccharide linked in turn to inositol of PI 4 She likes these Know them and study the figure with them K Proteins that redistribute membrane lipids i III ATP dependent flippases move PS and some PE from the outer leaflet to the inner leaflet ii ATP dependent floppases move amphiphilic lipids including cholesterol PC and sphingomyelin from the inner leaflet to the outer leaflet of the membrane iii Bidirectional scramblases Ca2 activated but ATP independent randomize lipids across the membrane and thus degrade membrane lipid asymmetry L Solid ordered state i the lipid chains are tightly packed and undergo relatively little motion ii Lipid