Fats They are nonpolar molecules that are not soluble in water – Are lipids that can store a great deal of energy –Contains three fatty acids bonded to a glycerol molecule backbone (don’t worry…I’ll show you this) Phospholipids Steroids Waxes Other lipids include some light-absorbing compounds called pigments Lipids are large biomolecules composed mainly of carbon and hydrogen, with small amounts of oxygen. Oils

1) Storage - lipids are non-polar and so are insoluble in water. 2) High-energy store - they have a high proportion of H atoms relative to O atoms and so yield more energy than the same mass of carbohydrate 3) Thermal insulation – fat conducts heat very slowly so having a layer under the skin keeps metabolic heat in. 4) Electrical insulation – the myelin sheath around axons prevents ion leakage, and increases signal speed. 5) Waterproofing – waxy cuticles are useful, for example, to prevent excess evaporation from the surface of a leaf. 6) Hormone production – steroid hormones. Estrogen requires lipids for its formation, as do other substances such as plant growth hormones. 1 gram of fat provides 9 kcal while 1 gram of carbohydrate or protein provides 4 kcal

Fats and oils are made from two kinds of molecules: glycerol (a type of alcohol with a hydroxyl group on each of its three carbons) and three Since there are three fatty acids attached, these are known as triglycerides. fatty acids joined by dehydration synthesis. The main distinction between fats and oils is whether they’re solid or liquid at room temperature, and this is based on differences in the structures of the fatty acids they contain.

The “tail” of a fatty acid is a long hydrocarbon chain, making it hydrophobic. Fatty acids are the main component of soap, where their tails are soluble in oily dirt and their heads are soluble in water to emulsify and wash away the oily dirt. However, when the head end is attached to glycerol to form a fat, that whole molecule is hydrophobic. Glycerol Backbone Hydrophobic means fear of water…so the tail end of a fatty acid is nonpolar, and will not associate with water at all. The “head” of the molecule is a carboxyl group which is hydrophilic. Hydrophilic means water friendly…so the head end of a fatty acid will readily associate with water.

Saturated fatty acids – straight molecules –Generally solid at room temperature Unsaturated fatty acids –Butter, lard, grease from cooked meats – Contain no double bonds between carbons –Some carbon atoms linked by a “double’ covalent bond –Generally liquid at room temperature –EX: olive oil, fish oils Hydrogenated vegetable oils contain naturally unsaturated fatty acids that have been saturated artificially and are generally solid at room temperature –EX: margarine, vegetable shortening

Phospholipids are made from The hydrocarbon tails of the fatty acids are still hydrophobic, but the phosphate group end of the molecule is hydrophilic because of the oxygens with all of their pairs of unshared electrons. glycerol two fatty acids, and (in place of the third fatty acid) a phosphate group with some other molecule attached to its other end. This means that phospholipids are soluble in both water and oil. This becomes especially important as we learn about cells, and the structure of their membranes.

Our cell membranes are made mostly of phospholipids arranged in a double layer with the tails of the fatty acids from both layers “inside” (facing toward each other) and the heads facing “out” (toward the watery environment) on both surfaces. Inside of cell Outside of cell CH 2 O P O O O CH CH 2 OO C O C O Phosphate Glycerol (a) Structural formula (b) Space-filling model Fatty acids (c) Phospholipid symbol Hydrophobic tails Hydrophilic head Hydrophobic tails – Hydrophilic head CH 2 Choline + Figure 5.13 N(CH 3 ) 3

Cholesterol is not a “bad guy!” Our bodies make about 2 g of cholesterol per day, and that makes up about 85% of blood cholesterol, while only about 15% comes from dietary sources. Cholesterol is the precursor to our sex hormones and Vitamin D. Vitamin D is formed by the action of UV light in sunlight on cholesterol molecules that have “risen” to near the surface of the skin. Our cell membranes contain a lot of cholesterol (in between the phospholipids) to help keep them “fluid” even when our cells are exposed to cooler temperatures. Steroids may be recognized by their skeleton, consisting of three fused six-membered and one five- membered ring

Waxes are widely distributed in nature. The leaves and fruits of many plants have waxy coatings, which may protect them from dehydration and small predators. The feathers of birds and the fur of some animals have similar coatings which serve as a water repellent. Cuticle Ocotillo Cacti Cuticle

Lipoproteins are clusters of proteins and lipids all tangled up together. These act as a means of carrying lipids, including cholesterol, around in our blood. There are two main categories of lipoproteins distinguished by how compact/dense they are. LDL or low density lipoprotein is the “bad guy,” being associated with deposition of “cholesterol” on the walls of someone’s arteries. HDL or high density lipoprotein is the “good guy,” being associated with carrying “cholesterol” out of the blood system, and is more dense/more compact than LDL.

Many plant pigments, such as anthocyanins, chlorophylls A and B, carotenoids and xanthophylls are lipids. Xanthophylls and melanins Some lipid pigments can also appear in animals, like cichlids…and people.