Lipids What are the kinds of lipids? Lipids Fats Waxes Steroids Phospholipids Lipids What are lipids? Lipids are hydrophobic molecules composed of carbon, hydrogen and oxygen. They contain fewer polar O-H bonds and more nonpolar C-H bonds than do carbohydrates, thus they are insoluble in water but soluble in nonpolar substances. Why are lipids important? Organisms use lipids for: 1. Storing energy 2. Building membranes and other cell parts Energy Units One calorie = 1 cal = 4.18 J One Kilocalorie = 1 Kcal = 1 Cal =4.18 KJ 1g of fat = 9 Kcal 1g of protein = 4 Kcal 1g of carbohydrates = 4 Kcal * The calorie is not an SI unit What are the most common fats found in plants and animals? Are the triacylglycerols (triglycerides), which contain three fatty acids attached to a single molecule of glycerol. The structure of glycerol and triglycerides: H l H – C – OH l H – C – OH l H – C – OH l H glycerol H l H – C – O – fatty acid l H – C – O – fatty acid l H – C – O – fatty acid l H triglyceride How do fatty acids attach to glycerol? Fatty acids attach to glycerol through a condensation reaction that takes place between the hydroxyl group of glycerol and the carboxyl group of fatty acids, the resulting bond is called an ester linkage, and the process is called esterification. Dehydration synthesis Saturated and unsaturated fatty acids Saturated fatty acids: have only single bonds between the carbon atoms. e.g.: stearic acid Unsaturated fatty acids: have one or more carbon – carbon double bonds. e.g.: oleic acid Stearic acid C18H36O2 stearic acid Oleic acid oleic acid What is a wireframe or Kekule structure? A kekule structure or a wireframe is a short notation, where neither the carbon atoms nor the hydrogen atoms are shown in the diagram , the carbon atoms are assumed to exist at every free end or bend of the wireframe. 1) Triglycerides A saturated triglyceride Why are the unsaturated fatty acids liquids at room temperature? In the triglyceride molecule, the molecule bends at the carbon – carbon double bond of the fatty acid, these bends and kinks keep the fatty acid tails away from each other, reducing the number of Van Der Waals attractions that can form along their length, and hence are liquid at room temperature. What does hydrogenation of oils mean? Hydrogenation of oils is adding hydrogen atoms to the double bonds of unsaturated triglycerids to change them into semisolid materials such as margarine and shortening. 2) Phospholipids Phospholipids are composed of a glycerol molecule to which is attached two fatty acids and a highly polar phosphate group. The phosphate group may be thought of as a polar head and the fatty acids as long nonpolar tails. The polar head is hydrophilic and the nonpolar tails are hydrophobic. Phospholipids and the cell membrane The cell membranes are mostly composed of phospholipids. 3) Steroids Steroids and the cell membrane Membranes also contain a class of lipids called sterols (steroids). These are compact hydrophobic molecules containing four fused hydrocarbon rings and several different functional groups. Cholesterol is an important steroid component of cell membranes. Phospholipids/Steroids and the cell membrane Steroids Estradiol Testosterone Cholestrol Progesterone Bile salts (Digestion of fats in small intestine) Sex hormones Vitamin D (Healthy Bones & teeth) 4) Waxes Are lipids containing long chain fatty acids linked to alcohols or carbon rings. They are hydrophobic molecules with firm pliable consistency, this property makes waxes ideally suited to form waterproof coating on various plant parts to conserve water and to prevent infection, they also cover some animal feathers and fur ( Penguin and Polar Bear). E.g.: the water resistant coat on cherries called cutin.