CHAPTER 8 unstable Lipid SAME solubility not water soluble 1. Fatty Acids Open chain Carboxylic acid 2. Triacylglycerols ESTER of glycerol + 3 fatty Saponification via boiling triglycerides with NaOH 3. Phosphoacylglycerols (Phospholipids) Glycerol – 1 phosphate – alcohol phosphatidic acid is produced. Waxes…. o Esters composed of long chain carboxylic acids with long alcohols o Used as protective coating for plants + animals Myricyl cerotate Carnauba wax - used for floor and car wax! Cetyl palmitate Spermaceti (taken from whales) - used for cosmetics Sphingolipids = contains a long chain amino alcohol known as sphingosine! (does NOT contain glycerol) Found in plants and animals, abundant in nervous system structurally similar to phospholipids Sphingosine Ceramide Sphingomyelin Glycolipids = compound where a carbohydrate is bound to an (OH) of a lipid Most often found as sugar (Glucose or Galactose) Derived from ceramides Glucocerebroside is an example! Gangliosides = Glycolipids with complex carbohydrate moiety that contains more than 3 sugars. Steroids = group of lipids that have fused ring structure of 3 six membered rings and ONE five-membered ring Cholesterol – must know how to draw! (easter egg) Sex Hormones Androgens are MALE sex hormones o synthesized in the testes o responsible for the development of male secondary sex characteristics o one example is our good friend testosterone! Estrogens are FEMALE sex hormones o synthesized in the ovaries o responsible for the development of female secondary sex characteristics and the control of the menstrual cycle. Lipid Bilayers polar surface of the bilayer contains charged groups hydrophobic tail is found in the INTERIOR of the bilayer Biological Membranes Every cell has a cell membrane Molecular basis of membrane structure is in the lipid component(s): o Polar head groups are in contact with the aqueous environment o Nonpolar tails are inside o The major force driving the formation of lipid bilayers is hydrophobic interactions o The arrangement of hydrocarbon tails in the interior can be… RIGID = saturated fatty acids FLUID = unsaturated fatty acids Effect of Double Bonds on the Conformation of Fatty Acids KINK in hydrocarbon chain Causes DISORDER in packing against other chains Greater fluidity in the membranes because of the abnormal packing o look at CIS double bonds and the saturated fatty acid chains! Biological Membranes (animal versus plant) Plant membranes have a higher percentage of unsaturated fatty acids than animal membranes. Cholesterol is found in animals RATHER than plant membranes. Animal membranes are LESS fluid (more rigid) than plant membranes Prokaryotes contain no steroids and are MOST fluid Cholesterol Reduces Fluidity by stabilizing extended chain formations of fatty acid hydrocarbons tails. hydrophobic interactions Membrane Layers Inner + outer layers of bilayer membrane contain mixtures of lipids. Compositions on inside and outside of lipid bilayer can be different. o This is what distinguishes the layers. Temperature Transition in Lipid Bilayer ( heat = disorder in membranes ) Rigid = transition temperature Heat increases the mobility of the lipid chains dramatically. Fluid = transition temperature Membrane Proteins – two types, peripheral and integral. Functions 1. Transport substances ACROSS membrane 2. Act as receptor sites 3. Site of enzyme catalysis Peripheral Proteins (outside) bound by electrostatic interactions Can be removed by raising the ionic strength Integral Proteins (both / inside) bound tightly to the interior of the membrane can be removed by detergents removal generally denatures the protein Proteins can be anchored to membranes N-myristoyl- and S-palmitoyl anchoring motifs Anchors can be via N-terminal Gly Thioester linkage with Cys Fluid Mosaic Model : lateral motion of components in the membrane Fluid: lateral motion of components in the membrane o Proteins “float” in the membrane and can move along its plane. Mosaic: components in the membrane exist side by side, but are separate entities The structure is that of a lipid bilayer with NO complexes! Membrane Function: Membrane Transport Passive Transport = passive diffusion of uncharged species from high concentration to low concentration via carrier protein (NO energy required) Simple diffusion: molecule or ion moves through an opening in membrane Facilitated diffusion: molecule or ion is carried across a membrane via carrier / channel protein. NO ENERGY Active Transport = a substance is moved AGAINST the concentration gradient Primary active transport: transport is linked to the hydrolysis of ATP or other high energy molecule o NA+/K+ ion pump Secondary active transport: transport is driven by the H+ gradient NEEDS ENERGY Membrane Receptors Generally oligomeric proteins binding of a biologically active substance to a receptor initiates an action within the cell Lipid-Soluble Vitamins divided into two classes: water soluble and fat soluble (lipid) 4 different vitamins – A, B, E and K Vitamin A Vitamin A ( retinol ) occurs only in the animal world. Extensively unsaturated hydrocarbon (B-carotene) Vitamin A is found in the plant world in the form of a provitamin in a group of pigments called carotenes (yellow +orange pigmented food) Enzyme-catalyzed cleavage of B carotene followed by reduction gives 2 molecules of Vitamin A (retinol) The best understood role of vitamin A is its participation in the visual cycle in rod cells The active molecule is retinal (vitamin A aldehyde) Retinal forms an imine with an –NH2 groups of the protein opsin to form the visual pigment called rhodopsin The primary chemical even of vision in rod cells is absorption of light by rhodopsin followed by isomerization of the 11-cis double bond to the 11trans double bond. Vitamin D A group of structurally related compounds that are involved in the regulation of calcium and phosphorous metabolism The most abundant form in the circulatory system is VIT D!! Vitamin E The most active form of vitamin E is alpha tocopherol Vitamin E is an antioxidant; traps H00· and ROO· radicals formed as a result of oxidation by O2 of unsaturated hydrocarbon chains in membrane phospholipids. Vitamin K Vitamin K has an important role in BLOOD clotting Long unsaturated hydrocarbon side chain consists of repeating isoprene units Prostaglandins Prostaglandins: a family of compounds that have the 20-carbon skeleton of prostanoic acid First detected in seminal fluid from prostate. The metabolic precursor is arachidonic acid Production of prostaglandins from arachidonic acid occurs in several steps. Leukotrienes Compounds also derived from arachidonic acid. Found in white blood cells Consists of 3 conjugated double bonds An important property is constriction in smooth muscles, ESPECIALLY the lungs!