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)