LipidsLipids

ObjectivesObjectives

• 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.

LIPIDSLIPIDS

From the Greek lipos meaning fat.

Varied structure

Many insoluble in water ─ lack polar groups.

Types of LipidsTypes 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 LipidsTypes 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

TriglyceridesTriglycerides(Fats and Oils)(Fats and Oils)

Saturated animal fats Saturated animal fats are associated with are associated with circulatory disorderscirculatory disorders

Plant oils can substitute Plant oils can substitute for animal fats in the for animal fats in the diet.diet.

Animation: FatsAnimation: Fats

TriglyceridesTriglycerides

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

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

Triglycerides Triglycerides (Triacylglycerolc)(Triacylglycerolc)

FATTY ACIDFATTY ACIDA lipid monomerA lipid monomer

Fatty acidFatty acid - long hydrocarbon - long hydrocarbon chain, carboxyl (-COOH), chain, carboxyl (-COOH), [acid] group at one end.[acid] group at one end.

Carboxyl group is polar, fatty Carboxyl group is polar, fatty acids are soluble in water.acids are soluble in water.

Most fatty acids in cells Most fatty acids in cells contain 16 to 18 carbons contain 16 to 18 carbons atoms per molecule.atoms per molecule.

FATTY ACIDFATTY ACIDSaturated Saturated

Only single bonds between Only single bonds between atoms. (NO doubles)atoms. (NO doubles)

UnstaturatedUnstaturated Double bonds in the carbon Double bonds in the carbon chain .chain .

Fig. 5-12a

(a) Saturated fat

Structuralformula of asaturated fatmolecule

Stearic acid, asaturated fattyacid

Fig. 5-12b

(b) Unsaturated fat

Structural formulaof an unsaturatedfat molecule

Oleic acid, anunsaturatedfatty acid

cis doublebond causesbending

GlycerolGlycerolA lipid monomerA lipid monomer

Water soluble

Three hydroxyl groups

FatsFats

Triglycerides with saturated fatty acids (e.g. butter is Triglycerides with saturated fatty acids (e.g. butter is solid at room temperature) solid at room temperature)

Animals use fat rather then glycogen long-term energy Animals use fat rather then glycogen long-term energy storage; fat stores more energy.storage; fat stores more energy.

OilsOils

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

Fatty AcidsFatty Acids++

GlycerolGlycerol

TriglyceridesTriglycerides

OilsOilsFatsFats

Saturated Fatty AcidsSaturated Fatty Acids Unsaturated Fatty Unsaturated Fatty AcidsAcids

Fats and OilsFats and Oils

WAXESWAXES

• Long-chain of fatty acids bonded to a long chain Long-chain of fatty acids bonded to a long chain alcohol.alcohol.

• Solid at room temperatureSolid at room temperature• High melting point High melting point • Waterproof Waterproof • Resist degradation.Resist degradation.• Form protective coveringsForm protective coverings

– Retards water loss in plantsRetards water loss in plants– Maintain animal skin and fur.Maintain animal skin and fur.

PHOSPHOLIPIDSPHOSPHOLIPIDS

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

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

PHOSPHOLIPIDSPHOSPHOLIPIDS

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 bilayerPhospholipid bilayer..

STEROIDSSTEROIDS

Differ from neutral fats - backbone of four fused carbon rings

Functions vary according to attached functional groups.

STEROIDSSTEROIDS

CholesterolCholesterol part of an animal part of an animal cell membrane.cell membrane.

Precursor of other steroids, Precursor of other steroids, including aldosterone and sex including aldosterone and sex hormones.hormones.

STEROIDSSTEROIDS

TestosteroneTestosterone is the male sex hormone.

ProgesteroneProgesterone is the female sex hormone.

TerpenesTerpenes

• ChlorophyllChlorophyll - plant pigment

•RhodopsinRhodopsin - visual pigment of the eye.

ReviewReview

• 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.