BIOL1005 Lecture 5 Lipids PDF

BIOL1005 Lecture 5 What are lipids? Lipids are a family of biomolecules that have common property of being soluble in solvents but not in water Lipid from Greek work “lipos” meaning fat or lard Lipids are widely distributed in nature both in plants and in animals The lipid content of a ce...

BIOL1005 Lecture 5 What are lipids? Lipids are a family of biomolecules that have common property of being soluble in solvents but not in water Lipid from Greek work “lipos” meaning fat or lard Lipids are widely distributed in nature both in plants and in animals The lipid content of a cell can be extracted using an organic solvent Lipids are important feature in cell membranes, fat-soluble vitamins, and steroid hormones Lipids come from fats in foods Found in meat, fish, oils, avocados, eggs, legumes (nuts) Properties of lipids 1. Insoluble in water, but soluble in organic solvent 2. It can be used as sources of energy by animals 3. Made up of fatty acids Classes of lipids Basic fatty acids Waxes Triglycerides (fats & oils) Phospholipids Glycolipids Steroids  Classes of lipids Waxes: fatty acid + long-chain alcohol Triglycerides: (fats & oils): glycerol + 3 fatty acids Phospholipids: glycerol + 2 fatty acids + phosphate + amino alcohol Glycolipids: glycerol or spinogosine + fatty acid + monosaccharide Steroids: 3 cyclohexanes + 1 cyclopentane fused together Fatty acid is the major component of lipids A carboxylic acid with long aliphatic chain Saturated: all single bonds Unsaturated: at least 1 double Polyunsaturated (2 or more double bonds) Most double bonds are cis- bonds that cause a bend in the chain Properties of fatty acids Saturated fatty acids are solid at room temperature and have a high melting point Unsaturated fatty acids are liquid at room temperature and have a low melting point Fatty acids  of carbon-carbon________________ _______________. Classification of fatty acids Saturated and Unsaturated Fatty Acids Fatty acids in the human body Essential fatty acids: Polyunsaturated fatty acids that the body cannot make e.g. Linoleic acid and Linolenic acid Lack of these in infants result in skin dermatitis  Cis- and trans- fatty acids (dbl bonds) H same side H opposite side Cis- makes a “kink” Fatty acids arrangements Saturated fatty acid unsaturated fatty acid  Interactions between fatty acids teractions Between Fatty Acids: London Forces Max dispersion forces when tightly packed Packed less tightly Think about it: Explain why stearic acid had a higher melting point than lauric acid. Fat Oil Fats and oils  Triglycerides Triglycerides Animal fats and vegetable oils are _______________________ (or triacylglycer fatty acid residues are joined to glycerol by ester bonds. Triglycerides Triglycerides make up fats and oils Hydrogenation of oils Partial hydrogenation of triglycerides What are trans-fat? Naturally occurring unsaturated fatty acids altered by partial hydrogenation, they are converted to saturated fatty acids, which will straighten the chains and change the physical properties (e.g. increase MP) Cis- becomes trans- Trans-fat have both the benefits and drawbacks of a saturated fat -longer shelf-life, solid at RT -tends to raise LDL-cholesterol and lower good-HDL Found in margarine, baked goods such as pastry and doughnuts, deep-fried chicken, snack chips, etc  Steroids Steroids Steroids  Cholesterol is the steroid found most often in humans and other animals. Cholesterol Regardless of what you eat, your body will contain some cholesterol, because it is manufactured in the liver. In cholesterol, the nonpolar rings and A steroid found most oftenchain hydrocarbon in humans andandmost are hydrophobic the - OH group, which makes up a much smaller animals part of the molecule, is hydrophilic. The body will contain some Overall, cholesterol, this makes because it is the molecule hydrophobic. manufactured in the The liver, primary regardless biological use ofof what isyou cholesterol as theeat starting material for the biosynthesis of other In cholesterol, the _______________. nonpolar rings and hydrocarbon are hydrophobic, and the OH isgroup Cholesterol (a much a component smaller part of cell membranes. of the molecule), is hydrophilic However, overall is hydrophobic Functions of cholesterol In cell membranes, gives it strengths Also found in myelin sheaths, bile salts, vitamin D (produced by the skin) Excess in cholesterol → gall stones and plaques in arteries The primary biological use of cholesterol is as the starting material for the biosynthesis of other steroids -precursor of bile salts -percursor of steroid hormones -precursor of vitamin D, cardiac glycosides Required for nerve transmission, particularly abundant in nervous tissues Summary Fatty Acids – major component of Lipids - Basic structures - Saturated vs Unsaturated Classes - Triglycerides - fats & oils - Steroids – cholesterol and hormones