PTT103 PTT103 BIOCHEMISTRYBIOCHEMISTRY

LIPIDLIPID

Pn Khadijah Hanim Abdul RahmanSchool of Bioprocess Engineering

Week 5: 8/10/2012Sem 1, 2012/2013

Course outcomeCourse outcome

Able to differentiate basic structure, properties, functions and classification of important biomolecules.

Content:- Structure and function of lipids and

their derivatives- Classification of lipids

OutlineOutlineLipid Classes- Fatty acids and their derivatives- Triacylglycerols- Wax esters- Phospholipids- Sphingolipids- IsoprenoidsMembranes- Membrane structure- Membrane function

IntroductionIntroductiondiverse group of biomoleculeseg. Fats, oils, phospholipids,

steroids, carotenoids- which differ in structure and function are considered as lipids

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 and sphingolipids)

◦Fats and oil means to store energy (e.g triacylglycerols)

◦chemical signals, vitamins, or pigments,

◦protective molecules (outer coatings for cells).

Lipid classesLipid classesLipids may be classified into

following classes:Fatty acids and their derivativesTriacylglycerolsWax estersPhospholipidsSphingolipidsIsoprenoids

Fatty acids and their Fatty acids and their derivativesderivativesFatty acids – monocarboxylic

acids that contain hydrocarbon chains of variable length (12-20 C), R-COOH

Fatty acids are important components of several types of lipid molecules

Occur primarily in triacylglycerols and several types of membrane bound lipid molecules.

Fatty acids and their Fatty acids and their derivativesderivatives

Naturally occurring fatty acids have an even no of C atoms that form unbranched chain.

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

Naturally occurring FA are in cis-configuration

The presence of cis double bond causes ‘kink’ in FA chain

Thus, unsaturated FA do not pack closely together as saturated FA.

Less energy is required to disrupt the intermolecular forces between unsaturated FA- lower melting point

Examples of fatty acidsExamples of fatty acids

number of double bonds.

position of a double bond

Tot number of C

Fatty acid with one double bond are referred to as monounsaturated molecules

When two or more double bonds occur in FA usually separated by methyl group- polyunsaturated.

Plants & bacteria synthesize all fatty acids they need from acetyl-CoA.

Mammals can synthesize saturated & some monounsaturated fatty acid. Other unsaturated FA obtain from dietary source.

Nonessential FA – can be synthesizedEssential FA – eg: linoleic and

linolenic acids are obtained from diet (vege oils,nuts,seeds)

Linoleic and linolenic acids: membrane structure, precursors for several important metabolites.

Symptoms of low-fat diets – deficient in essential FA:

Dermatitis (scally skin)Poor wound healingReduced resistant to infectionHair lossThrombocytopenis (reduction in no of

platelets)

TriacylglycerolsTriacylglycerolsEster of glycerol with 3 fatty acids

moleculesNeutral 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 FAOils – liquid at room temp, high unsaturated FAIn animals triacylglycerols (fats)

- store energy > efficiently than glycogen:1.TAGs are hydrophobic, they coalesce into

compact, anhydrous droplets within cells. Adipocyte stores TAG.

- Glycogen binds to water- the anhydrous TAG store equivalent amount of energy in about 1-8th of glycogen vol.

2. TAG are less oxidized than carbohydrate. TAG release more energy when they are degraded.

provide insulation at low temp- poor conductor of heat. Adipose tissue prevent the heat loss.

In plants triacylglycerols (oils)- energy reserve in fruits and seeds- high amounts of unsaturated FA- plant oils (eg oleic & linoleic) soybean, peanut, olive

Wax estersWax estersare esters formed from fatty acids and

long chain alcoholsNonpolar lipidFunction – protective coating on leaves,

stems, fruits, skin and fur of animalscarnauba wax produced by the leaves

of Brazilian wax palm – 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)◦They form bimolecular layers: (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 instead of glycerol, fatty acids, phoshate, alcohol(classified as sphingolipid) – discuss later

Phosphoglycerides

The simplest phosphoglyceride- phosphotidic acid (precursor for all phosphoglyceride molecules).

Phosphatidic acid is composed of glycerol-3-phosphate that is esterified with 2 FAs.

CO

O

CH

CH2

CH2 O

O

R

O P

O

O-

O X

R2

Basic Structure of phosphoglyceride

SphingolipidsSphingolipids

Important membrane components of animal & plant membranes

Contain long-chain amino alcohol (either sphingosine or phytosphingosine) linked to fatty acid mol by amide bond

3 subclasses – ceramide (core of sphingolipid), sphingomyelin (found in animal cells), glycosphingolipid

Sphingolipid Components

Sphingomyelin – animal cell membrane: found in greatest abundance in myelin sheath of nerve cells.- have a phosphorylcholine or phosphoethanolamine molecule with an ester linkage to the 1-hydroxy group of a ceramide.

Ceramide are also precursors for glycolipids or refered as glycosphingolipid

- In glycolipids: monosaccharide, disaccharide and oligosaccharide is attached to ceramide thru O-glycosidic linkage.

- Glycolipids differ from sphingomyelin: contain no phosphate.

Classes :-- Cerebrosides have a single glucose or galactose at

the 1-hydroxy position- Sulfatides are sulfated cerebrosides- Gangliosides sphingolipids that possess

oligosaccharide groups, 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 (enormous group of molecules that are found largely in essential oils of plants)

- Classified according to number of isoprene residues they contain :

- Monoterpenes (2 isoprene units- 10 Cs)

eg. geraniol in oil of geranium- Sesquiterpenes (3 isoprenes)

eg. Farnesene (part of citronella oil- used in soaps and perfumes)

- 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 (derivatives of the hydrocarbon ring system of cholesterol)

- Complex derivatives of triterpenes (6 Cs)- 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 all steroid hormones, vit D & bile salts.

- Possesses 2 methyl (C-18 & C-19), attached to C-13 & C-10 & a double bond

- Has a OH group (sterol)- Cholesterol often stored in the cells as

a fatty acid ester.- The esterification reaction is catalyzed

by the enzyme acyl-CoA acyltransferase.

Animal SteroidsAnimal Steroids

LIPOPROTEINSLIPOPROTEINSLipoproteins- describe the protein that is

covalently linked to lipid groupsCommonly found in the blood plasma of

mammals. Plasma lipoproteins transport lipid

molecules (TAG, phospholipids & cholesterol) thru the bloodstream from 1 organ to the other.

Protein components of lipoprotein- apoprotein

Lipoproteins are classified according their density

Types of lipoproteinsTypes of lipoproteinsChylomicrons- large lipoproteins of extremely low

density.- Transport dietary TAG and cholesteryl esters from

intestine to muscle and adipose tissues.Very low density lipoproteins (VLDL)- synthesized in

the liver, transport lipids to tissues.- As VLDL are transported thru the body, they

become depleted of TAGs and some apoprotein and phospholipids.

- Eventually, the TAG-depleted VLDL remnants are either picked up by the liver or converted to LDL. LDL carry cholesterol to tissues.

- LDL are engulfed by cells after binding to LDL receptors.

High-density lipoprotein (HDL)- also produced in liver.

- Cholesteryl esters are formed when the plasma enzyme lecithin:cholestero acyltransferase transfers a FA residue from lecithin to cholesterol.

- HDL transport these cholesteryl ester to liver.

- Liver can dispose cholesterol, convert most of it to bile salts.

AtheroscelerosisAtheroscelerosisChronic disease in which soft masses/plague

accumulate on the inside of arteries. During plaque formation- smooth muscle cells,

macrophages and various cell debris built up.As they are filled with lipid- they take a foam

like appearance. Eventually, the plaque may calcify and

protrude sufficiently into arterial lumens that blood flow impeded.

Common consequences of atherosclerosis- coronary artery disease- damages heart muscle.

Most of the cholesterol found in plaque is obtained by the ingestion of LDL by foam cells- directly correlated with high risk for coronary heart disease.

High plasma HDL- low risk for coronary artery disease.

Liver cells are the only cells that possess HDL receptors.

QuestionsQuestionsClassify and differentiate lipid

classesWhat role do plasma lipoproteins

play in human body? Why do plasma lipoproteins require a protein component to accomplish their role?