Lipids

Objectives Identify, by name and skeleton structure, the 4 general classes of lipids. Describe the general chemical characteristics of the 4 classes. Identify the monomers and the biochemical processes that form fat polymers. Identify and describe the typical function of each lipid class in biological systems.

LIPIDS From the Greek lipos meaning fat. Varied structure Many insoluble in water ─ lack polar groups.

Types of Lipids TriglyceridesTriglycerides –Most familiar lipids –Insulation –Energy reserves WaxesWaxes –Waterproof –Resistant to degradation PhospholipidsPhospholipids –Constructed similar to neutral fats –Polar –Plasma membrane constituent TerpenesTerpenes –Long-chains –Found in biological pigments (chlorophyll, rhodopsin) SteroidsSteroids –Different structure from fats (Carbon ring backbone) –Cell messengers

Types of Lipids TerpenesTerpenes –Long-chains –Found in biological pigments (chlorophyll, rhodopsin) PostglandinsPostglandins –Nonpolar tails on a 5-carbon ring –Local chemical messengers SteroidsSteroids –Different structure from fats (4 Carbon ring backbone) –Cell messengers

Triglycerides (Fats and Oils) Saturated animal fats are associated with circulatory disorders Plant oils can substitute for animal fats in the diet. Animation: Fats Animation: Fats

Triglycerides Contain two types of unit molecules (monomers) fatty acids and glycerol.

Gylcerol (monomer) joined to three fatty acids (monomer) by dehydration (condensation) synthesis. Triglycerides (Triacylglycerolc)

FATTY ACID A lipid monomer Fatty acid - long hydrocarbon chain, carboxyl (-COOH), [acid] group at one end. Carboxyl group is polar, fatty acids are soluble in water. Most fatty acids in cells contain 16 to 18 carbons atoms per molecule.

FATTY ACID Saturated Only single bonds between atoms. (NO doubles) Unstaturated Double bonds in the carbon chain.

Fig. 5-12a (a) Saturated fat Structural formula of a saturated fat molecule Stearic acid, a saturated fatty acid

Fig. 5-12b (b) Unsaturated fat Structural formula of an unsaturated fat molecule Oleic acid, an unsaturated fatty acid cis double bond causes bending

Glycerol A lipid monomer Water soluble Three hydroxyl groups

Fats Triglycerides with saturated fatty acids (e.g. butter is solid at room temperature) Animals use fat rather then glycogen long-term energy storage; fat stores more energy.

Oils Triglycerides with unsaturated fatty acids (e.g. Corn oil is liquid at room temperature). Animals use fat rather then glycogen long-term energy storage; fat stores more energy.

Fatty Acids +Glycerol Triglycerides Oils Fats Saturated Fatty Acids Unsaturated Fatty Acids Fats and Oils

WAXES Long-chain of fatty acids bonded to a long chain alcohol.Long-chain of fatty acids bonded to a long chain alcohol. Solid at room temperatureSolid at room temperature High melting pointHigh melting point WaterproofWaterproof Resist degradation.Resist degradation. Form protective coveringsForm protective coverings –Retards water loss in plants –Maintain animal skin and fur.

PHOSPHOLIPIDS Differ from neutral fats - one fatty acid is replaced by phosphate group or a group with both phosphate and nitrogen.

Phosphate group is the polar head; hydrocarbon chains become nonpolar tails.

PHOSPHOLIPIDS  In aqueous environments, arrange in a double layer. Polar (hydrophilic) heads toward water molecules.  Nonpolar (hydrophobic) tails face toward each other - away from water molecules. Very important property! Results in formation of an interface or separation between two solutions (e.g. The interior and exterior of a cell

Phospholipid bilayer.

STEROIDS Differ from neutral fats - backbone of four fused carbon rings Functions vary according to attached functional groups.

STEROIDS Cholesterol part of an animal cell membrane. Precursor of other steroids, including aldosterone and sex hormones.

STEROIDS Testosterone Testosterone is the male sex hormone. Progesterone Progesterone is the female sex hormone.

Terpenes Chlorophyll Chlorophyll - plant pigment RhodopsinRhodopsin - visual pigment of the eye.

Review Name the 4 general classes of lipids. Describe their basic structures Describe the general chemical characteristics of the 4 classes of lipids Identify the monomers for the production of triglycerides, fats, and oils. Describe the biochemical processes that form fat polymers. Identify and describe the typical function of each lipid class in biological systems.