ptt103 biochemistry lipid pn khadijah hanim abdul rahman school of bioprocess engineering week 5:...
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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?