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PTT103 PTT103 BIOCHEMISTRYBIOCHEMISTRY
LIPIDLIPID
Pn Syazni Zainul KamalSchool of Bioprocess Engineering
Course outcomeCourse outcome
Able to demonstrate basic structure, properties, functions and classification of important biomolecules
OutlineOutlineLipid Classes- Fatty acids and their derivatives- Triacylglycerols- Wax esters- PhospholipidsMembranes- Membrane structure- Membrane function
IntroductionIntroductiondiverse group of biomoleculeseg. Fats, oils, phospholipids,
steroids, carotenoidsLipids – Those substances from
living organisms that dissolve in nonpolar solvents eg. Ether, chloroform, acetone but not in water.
Role & function as : ◦structural components in cell membranes (e.g phospolipids)
◦means to store energy (e.g triacylglycerols)
◦chemical signals, vitamins, or pigments,
◦protective molecules (outer coatings for cells).
Lipid classesLipid classesFatty acids and their derivativesTriacylglycerolsWax estersPhospholipidsSphingolipidsIsoprenoids
Fatty acids and their Fatty acids and their derivativesderivatives
Fatty acids – monocarboxylic acids that contain hydrocarbon chains of variable length (12-20 C), R-COOH
2 types saturated (only carbon-carbon single bond)
unsaturated (one/more double bonds)
- can occur in two isomeric forms; cis/trans
- cis : identical groups are on the same side of a double bond
- Trans : identical groups are on opposite sides of a double bond
Cis-isomers : Both R groups are on the same side of the carbon-carbon double bond
Trans-isomers : Have R groups on different sides.
Monounsaturated : 1 double bondPolyunsaturated : > 1 double bonds
Fatty acid structure
Examples of fatty acidsExamples of fatty acids
number of double bonds.
position of a double bond
Tot number of C
Plants & bacteria synthesize all fatty acids
Mammals can synthesize saturated &monounsaturated fatty acid. Other unsaturated FA obtain from dietary
Nonessential FA – can be synthesized
Essential FA – obtain from diet (vege oils,nuts,seeds)
Unsaturated FA do not pack as closely together as saturated fatty acids Less energy is required to disrupt the intermolecular forces between them have lower melting points and are liquids at room temperature. For example, palmitic acid A6:0), a saturated fatty acid, melts at, whereas palmitoleic acid A6:1A9) melts at 0°C
TriacylglycerolsTriacylglycerolsEster of glycerol with 3 fatty acidsNeutral fats – no chargeMost contain FA of varying lengths,
which may be saturated, unsaturated or a combination of both
Referred as fats or oils depend on FA composition
Fats – solid at room temp, mostly saturated FA
Fats – solid at room temp, mostly saturated FA
Oils – liquid at room temp, high unsaturated FA
In animals triacylglycerols (fats) - store energy > efficiently than glycogen- provide insulation at low temp
In plants triacylglycerols (oils)- energy reserve in fruits and seeds- high amounts of unsaturated FA (eg oleic & linoleic) soybean, peanut, olive
Wax estersWax esters
are esters formed from fatty acids and long chain alcohols
Nonpolar lipidFunction – protective coating on
leaves, stems, fruits, skin and fur of animals
carnauba wax – 32C carboxylic acid & 34C alcohol component
Beeswax – 26C carboxylic acid & 30C alcohol component
PhospholipidsPhospholipidsRoles :
1) Structural components of membranes2) Emulsifying agents3) Surface active agents (substance that lowers surface tension of a liquid)
Amphipathic moleculeHave hydrophobic and hydrophilic
domains
Hydrophobic domain- composed of hydrocarbon chains of fatty acids
Hydrophilic domain (polar head group)- composed of phosphate & other charged or polar group
Suspended in water they spontaneously rearrange into ordered structures◦Hydrophobic group exclude water◦Hydrophilic group exposed to water (Next
slide)◦(Basis of membrane structure)
Phospholipid in aqueous solution
2 types phospholipids :
phosphoglycerides – mol contain glycerol, fatty acids, phosphate, alcohol (eg choline). Found in cell membrane
Sphingomyelins – contain sphingosine, fatty acids, phoshate, alcohol(classified as sphingolipid) – discuss later
Phosphoglycerides
Phosphatidic acid – precursor for other phosphoglyceride mol
CH2
CH
CH2
O
O
O PO
CO
CO
R1
R2
OH
O
SphingolipidsSphingolipids
Important membrane components of animal & plant membranes
Contain log-chain amino alcohol (either sphingosine or phytosphingosine) linked to fatty acid mol by amide bond
3 subclasses – ceramide, sphingomyelin, glycosphingolipid
Sphingomyelin – animal cell membrane- have a phosphorylcholine or phosphoethanolamine molecule with an ester linkage to the 1-hydroxy group of a ceramide.
Glycosphingolipid- are ceramides with one or more sugar
residues joined in a β-glycosidic linkage at the 1-hydroxyl position.
- Classes :-- Cerebrosides have a single glucose or
galactose at the 1-hydroxy position- Sulfatides are sulfated cerebrosides- Gangliosides have at least three sugars,
one of which must be sialic acid
gangliosides
sulfatides
IsoprenoidsIsoprenoidsBiomolecules contain repeating 5
carbon structural units (isoprene units)
Biosynthetic pathway begin with formation of isopentenyl pyrophosphate from acetyl-CoA
Consist of terpenes and steroids
isoprene
Terpenes
- Classified according to number of isoprene residues they contain :
- Monoterpenes (2 isoprenes) eg. geraniol in oil of geranium
- Sesquiterpenes (3 isoprenes)eg. Farnesene (part of citronella
oil)- Diterpenes (4 isoprenes)
eg. Phytol, a plant alcohol
- Triterpenes (6 isoprene)eg. Squalene in shark liver
oil, olive oil- Tetraterpenes (8 isoprene)
eg. Carotenoids, orange pigment
- Polyterpene (Thousands isoprene)eg. Rubber (3000-6000
isoprene)
Steroids
- Complex derivatives of triterpenes- Eukaryotes & some bacteria- Composed of 4 fused rings - Distinguished from each other by
placement of carbon-carbon double bonds and various constituents (OH, Carbonyl & alkyl groups)
- Eg cholesterol, progesterone, testosterone, estradiol
Cholesterol- Important mol in animals cell
membrane & precursor for synthesis of vit D
- Possesses 2 methyl (C-18 & C-19), attached to C-13 & C-10 & a double bond
- Has a OH group (sterol)