LIPIDS13.1-13.2

13.1: WHAT ARE LIPIDS? Lipids have three important roles in

human biochemistry Energy is stored within fat cells

Help to separate aqueous solutions in cell membranes

They serve as chemical messengers

STORAGE Animals and humans store energy in

fat cells

When fats are burned, they produce twice as much energy as carbohydrates produced

MEMBRANE COMPONENTS Lipids are not water soluble due to the

polar groups being much smaller then the nonpolar parts

This makes them perfect for separating compartments within cells

MESSENGERS Serve as chemical messengers

Steroid hormones are primary messengers

Prostaglandins and thromboxanes are examples of secondary messengers who activate the hormones responses

CLASSIFICATION OF STRUCTURE Four lipid groups

Simple lipids(fats and waxes)

Complex lipids

Steroids

Prostaglandins, thromboxanes, and leukotrienes

13.2 STRUCTURE OF TRIGLYCERIDS Triesters of glycerol of long-chain

carboxylic acids Alcohol of triglycerides are always

glycerol Acid component may be any number of

fatty acids Animal fats and plant oils

TRIGLYCERIDES & FATTY ACIDS Unbranched carboxylic acids Chains from 10-20 carbons Even number carbon chains One functional group (OH – hydroxyl) Cis-isomer predominates

TRIACYLGLYCEROLS Triglycerides Most common lipid material Mono & triglycerides are not infrequent

HYDROPHOBIC Caused by long hydrocarbon Ester groups are buried in non-polar

environment Insoluble in water

13.3 PROPERTIES Fats are usually solid at room temp Liquids are oils (plant and fish)

PHYSICAL PROPERTIES Solid animal fats contain saturated

fatty acids Some have unsaturated

Vegetable oils contain high amounts of unsaturated fatty acids Some have saturated

Colorless, odorless, tasteless, Flavor is caused by other dissolved

substances

COCONUT AND VEGETABLE OIL Vegetable Oil

High amounts of unsaturated fatty acids Coconut Oil

Small amount of unsaturated fatty acids Rich in low-molecular-weight fatty acids (chiefly lauric acid)

ESSENTIAL FATTY ACIDS Unsaturated fatty acids Linoleic and linolenic aicds Body cannot synthesize these acids Obtained from our diet

POLYUNSATURATED Oils with an average of more than one

double bound per fatty acid chain

HYDROGENATION Reduce C-C double bonds to single

bonds Treated with hydrogen and a catalyst

Hydrogenate all double bonds, a fat with no double bonds may be too solid

Margarine – partial hydrogenation of veg oils Contains more unsaturation than fully

hydrogenated shortenings Source of trans fatty acids

SAPONIFICATION Glycerides are subjected to hydrolysis

Carried out by acids or bases Base-promoted hydrolysis of fats and

oils producing glycerol and a mixture of fatty acid salts Soaps