Chapter 13 Lipids

Tiara Bartol and Brant Houghton

13.1 What are lipids?

Family of substances that are insoluble in water but soluble in nonpolar solvents and solvents of low polarity

Defined in terms of properties

Classification of Function

3 roles Storage energy within fat cells Part of membranes that separate

compartments of aqueous solutions Serve as chemical messengers

Storage Important in animals Use fats for storage

Glycogen Greater amount of energy

9 Kcal/g

Membrane ComponentLipids lack water solubilityThe body needs insoluble

compounds for membranes that separate aqueous solutions

Derives from smaller polar groups than alkane like portions

Nonpolar provide hydrophobic part

MessengersPrimary messenger delivers

signals from one part of body to anotherSteroid hormones

Secondary messenger meditates hormonal responseprostaglandins and

thromboxanes

Classification by Structure

4 groupsSimple lipids

Fats and waxesComplex lipidsSteroidsProstaglandins, thromboxanes,

and leukotrienes

13.2 What are structures of Triglycerides?

TriglycerideAnimal fats and plant oilsTriesters of glycerol and long

chain carboxylic acids called fatty acids

Even number of acidsAka triacylglycerols3 groups of glycerol are esterifiedComplex mixturesMost cases 2 or 3 different fatty

acids are presentHydrophobic character is caused

by long chainEsters are buried in nonpolar

environment which makes them insoluble

Fatty acidsPractically all unbranched

carboxylic acids10 to 20 carbosnEven # of carbons

Cis isomer predominates Mono and diglycerides

Not infrequentLatter two sides

1 or 2 OH groups are esterified

13.3 What are properties of Triglycerides? Fats

A mixture of triglycerides containing a high proportion of long chain, saturated fatty acids

OilsA mixture of triglycerides

containing a high proportion of long chain, unsaturated fatty acids or short chain, saturated fatty acids

Physical StateFats are generally solids at room

temperatureFats from plants and fish are

liquidsLiquid fats are oilsSolid fats are mainly saturated

fatty acidsVegetable oil has high amounts of

unsaturated fatty acidsEssential fatty acids

The body needs but can’t synthesize

Most oils contain large amounts of unsaturated fatty acids

Coconut oil has a small amountPolyunsaturated fatty acids have

more than one double bondPure fats and oils are colorless,

odorless, and tastelessTo gain taste substances must be

added

HydrogenationEasy to convert unsaturated

liquids and oils to solidsDon’t hydrogenate all double

bonds It will become too solid

This is the source of trans fatty acids

SaponificationBase promoted hydrolysis of fats

and oilsProduce glycerol and a mixture of

fatty acids called soap It is the oldest known chemical

reaction