PTT103 BIOCHEMISTRY LIPID Pn Syazni Zainul Kamal School of Bioprocess Engineering

Course outcome Able to demonstrate basic structure, properties, functions and classification of important biomolecules

Outline Lipid Classes - Fatty acids and their derivatives - Triacylglycerols - Wax esters - Phospholipids Membranes - Membrane structure - Membrane function

Introduction diverse group of biomolecules eg. Fats, oils, phospholipids, steroids, carotenoids Lipids – 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 classes Fatty acids and their derivatives Triacylglycerols Wax esters Phospholipids Sphingolipids Isoprenoids

Fatty acids and their derivatives 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 bond Polyunsaturated : > 1 double bonds

Fatty acid structure

Examples 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

Triacylglycerols Ester of glycerol with 3 fatty acids Neutral fats – no charge Most 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

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 esters are esters formed from fatty acids and long chain alcohols Nonpolar lipid Function – 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

Phospholipids Roles : 1) Structural components of membranes 2) Emulsifying agents 3) Surface active agents (substance that lowers surface tension of a liquid) Amphipathic molecule Have 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

Sphingolipids 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

Isoprenoids Biomolecules 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 ( 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)