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
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