Fatty acids and lipids - Kauno technologijos universitetasjulivan/medical-chemistry/Lectures/Fatty acids - lipids...Classification of fatty acids • By saturation level of carbonyl

Fatty acids and lipids

Outline

• Structure of fatty acids • Physical properties of fatty acids • Classification of fatty acids • Chemical properties of fatty acids • Lipid classification • Glycerides • Sphingolipids • Cholesterol and its derivatives • Membranes

Fatty acids •Amphipathic and mono-functional compounds, containing nonpolar carbonyl chain and ionized carboxyl-group. In fact, they are long C atom-chain containing carboxylic acids. Number of C atoms is more 4 (in naturally ocuring 4-28C)

CH3(CH2)nCOOH – condensed formula

Extended structural formula

Physical properties

Physical properties Physical state– Short or middle-length chain FA are oily fluids ; long chain FA are solid. Poorly soluble or insoluble in water. Melting point depends on length and on saturation of carbonyl chain. Melting temperature increases with increasing of carbonyl-chain length and saturation degree.

Palmitic acid C-16 - solid

Butyric acid C-4 is oil

Classification of fatty acids

• By the length of carbonyl chains short chain fatty acids with 4 till 6 C

atoms middle chain length fatty acids with 8-12

C atoms. long chain fatty acids with more than 12

C atoms

Classification of fatty acids

• By saturation level of carbonyl chain saturated fatty acids (SFA) with only single

bonds between C atoms unsaturated fatty acids (UFA) monounsaturated fatty acids

(MUFA)with one double bond polyunsaturated (PUFA) with two or

several double bonds. Omega fatty acids.

Nomenclature of fatty acids No ofcarbonatoms

Commonname

Systematic name Formula Meltingpoint(°C)

Sources

Saturated fatty acids10 Capric Decanoic CH3(CH2)8COOH 32 Saw palmetto12 Lauric Dodecanoic CH3(CH2)10COOH 43 Coconut14 Myristic Tetradecanoic CH3(CH2)12COOH 54 Nutmeg16 Palmitic Hexadecanoic CH3(CH2)14COOH 62 Palm18 Stearic Octadecanoic CH3(CH2)16COOH 69 Animal fat20 Arachidic Eicosanoic CH3(CH2)18COOH 76 Peanut oil,

vegetable and fishoils

Monounsaturated fatty acids16 Palmitoleic Cis-9-hexadecenoic C15H29COOH 0 Butter18 Oleic Cis-9-octadecenoic C17H33COOH 13 Olives, cornPolyunsaturated fatty acids18 Linoleic 9,12-octadecadienoic C17H31COOH -9 Soybean,

safflower,sunflower

18 Linolenic 9,12,15-octadecatrienoic

C17H29COOH -17 Seed oils

20 Arachidonic 5,8,11,14-eicosatetraenoic

C19H31COOH -50 Traces in animalfats

Structure of saturated fatty acids

Hexadecanoic acid or palmitic acid in extended notation

Condensed notation

Line-angle notation

In shorthand system 16:0, where 16 denotes the number of C atoms And 0 denotes number of double bonds

Structure of mono-unsaturated fatty acids

Extended notation

Condensed notation

Line-angle notation

Cis-9-octadecenoic acid Oleic acid

Double bond in cis-configuration

In shorthand system 18:1( ∆9), where 18 denotes the number of C atoms, 1 denotes number of double bonds and ∆9 denotes location of double bond .

• Omega classification is based on specification of the endmost double bond in PUFA

Omega-classification of polyunsaturated fatty acids

ω-3

ω-6

ω-6

ω-6

A serie is characteristic to fish oil

A serie is characteristic to plant oil

Behaviour of SFA and UFA

Chemical properties of fatty acids • All types of acids undergo ionization in

water: • Oxidation: in organism fatty acids are total

decomposition by enzyme-catalyzed oxidation producing CO2 and H2O.

• Limited oxidation by loss of carboxylic-group (decarboxylation): under heating can be cleaved producing CO2.

• Esterification:

R C

O

OH+ R1 OH R C

O

OR1

+ OH2

R-COOH → CO2 + R-H

R-COOH ↔ R-COO- + H+

to

Lipids

Classification of lipids

• Classification of lipids is based on products of hydrolysis (this is breakdown by water).

• Triglycerides – glycerol and fatty acids are products of hydrolysis

• Phosphoglycerides – glycerol, fatty acids and phoshate are products of hydrolysis

• Sphingomyelins – alcohol sphingosine, fatty acids and phoshate are products of hydrolysis

• Glycolipids - alcohol sphingosine, fatty acids and sugar units are products of hydrolysis

• Steroids – non-hydrolysable, e.g. cholesterol • Waxes – long chain fatty acid and long chain

alcohol

Triglycerides (fats and oils)

A fat is a triacylglycerol that is solid at room temperature. An oil is a triacylglycerol that is usually liquid at room temperature.

Monoglyceride Diglyceride Triglyceride

Melting points of oils and fats

The difference between fats and oils is the melting point, which depends on the saturation of the fatty acids present in the compound

Chemical properties of triacylglycerols

Hydrolysis of triacylglycerols

2. Alkaline hydrolysis results in soap formation. This is saponification.

1. Acidic and enzymatic hydrolysis

Phosphoglycerides (glycerophospholipids)

Amino alcohol: choline (in lecitins) ethanolamine or serine (in cephalins or phosphatidyl- serine).

Ester bonds

Ionization of phosphoglycerides

• Diphilic compounds • Contain hydrophobic tailes and hydrophilic (polar) head

Lecithin (choline containing) and cephalin(ethanolamine containing)

phosphoglycerides

Sphingomyelins, a group of sphingolipids

•Present in membranes • Used primarily in nerve tissue - myelin sheath. • In people, 25% of all lipids are sphingolipids.

Glycolipids (1)

Steroids

Cholesterol

Properties of cholesterol • very hydrophobic • -OH group at 3C atom can form esters with carboxylic acids • a side chain can undergo oxidation and decomposition • the condensed ring structure is not destructible in human organism

It is an alcohol in which molecule OH-group is attached to steroid nucleus

• A structural component of plasma membranes

• A compound used for production of: hormones, bile acids, vitamine D3in

specialized tissues

Cholesterol in the body

Cholesterol provides rigidity to membranes

Waxes

Structure of a wax

A weak polar head

Non-polar tails

A component of bee-wax