Biochemistry Lipids 1 - uomustansiriyah.edu.iq · Biochemistry Lipids 1 2ndyear Biology ... •Biomolecules that contain fatty acids or a steroid nucleus. •Named for the Greek word

BiochemistryLipids1

2nd yearBiologyMustansiriyahUniversity

زھراء سالم محسن. عبیرحازم مصطفى د.د

1

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in Cum

mings

Lipids

Lipids are are non-polar (hydrophobic) compounds, soluble in organic solvents.

• Most membrane lipids are amphipathic, having a non-polar end and a polar end.

• Biomoleculesthatcontainfattyacidsorasteroidnucleus.

• NamedfortheGreekwordlipos,whichmeans“fat.”

• Extractedfromcellsusingorganicsolvents.2

Lipids are consist of fatty acids (F.As) as a building block and could be grouped as:

1. Neutral fats and oils (triglycerides)3. Phospholipid and sphingolipids 4. Waxes5. Steroids 6. Prostaglandins 6. Fat soluble vitamins

Lipids

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Lipids

Saponificationlipids

TriglycerideOil+fat

Waxes

Phospholipids

SphingolipidsNon-saponification

lipids

Steroids Prostaglandins

Classes of Lipids

LipidsFattyAcids(F.As)

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Fatty acids (F.As) : a hydrocarbon chain with a carboxylic acid at one end.

A 16-C fatty acid:

CH3(CH2)14-COO-

Non-polar polar

OH

O

F.AsFormulas

TheformulasforF.Asarewrittenas• Condensedformulas.• Line-bondformulas.• Forexamplecaprylic acidwith8carbonatoms.CH3—(CH2)6—COOH

CH3—CH2—CH2—CH2—CH2—CH2—CH2—COOH

7OH

O

FattyAcids

F.As• Arelong-chaincarboxylicacids.

• Typicallycontain12-18carbonatoms.

• Arewaterinsoluble.• Canbesaturatedorunsaturated.

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Saturated Fatty Acids

CH3 CH2 CH2 CH2 CH2 CH2 CH2 C OHO

1245678 3

Octanoic Acid

Unsaturated Fatty Acids

CH3 CH2 CH2 CH2 CH2 CH2 CH2 C OHO

1245678 3

CH3 CH2 CH2 CH2 CH2 CH2 CH2 C OHO

1245678 3

3 - Octenoic Acid

3, 6 - Octadienoic Acid

Short hand: 8:1 (D3)

8:2 (D3,6)

Cis 9 - Octadecenoic Acid (oleic)

Trans 9 - Octadecenoic Acid (elaidic acid)

O

CH3(CH2)7 C C (CH2)7 C OHHH

910

OCH3(CH2)7 C C (CH2)7 C OH

H

H

Cis And Trans Fatty Acids

A 16-C fatty acid with one cis double bond between C atoms 9-10 may be represented as 18:1 cis D9.

A 16-C fatty acid with one trans double bond between C atoms 9-10 may be represented as 18:1 trans D9.

Saturated Fatty Acids

Saturatedfattyacids have• SingleC–Cbonds.• Moleculesthatfitcloselytogetherinaregularpattern.

• Strongattractionsbetweenfattyacidchains.

• Highmeltingpointsthatmakethemsolidsatroomtemperature.

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Some Saturated Fatty Acids

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Unsaturated Fatty Acids

Unsaturatedfattyacids• HaveoneormoredoubleC=Cbond.

• Typicallycontaincisdoublebonds.

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PropertiesofUnsaturatedFattyAcids

Unsaturatedfattyacids• Have“kinks”inthefattyacidchains.

• Donotpackclosely.

• Havefewattractionsbetweenchains.

• Havelowmeltingpoints.

• Areliquidsatroomtemperature.

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“kinks” in chain

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Polyunsaturated Fatty Acids

Linoleic acid: Cis, cis, 9, 12 - Octadecadienoic acid

Linolenic acid: Cis, cis, cis 9, 12, 15 - Octadecatrienoic acid

Arachidonic acid: Cis, cis, cis, cis 5, 8, 11, 14 - Eicosatetraenoic acid

Linoleic Acid

Linolenic Acid

Arachidonic Acid

Somefattyacidsandtheircommonnames:14:0 myristic acid;16:0palmitic acid;18:0 stearic acid;18:1cisD9 oleicacid18:2cisD9,12 linoleic acid18:3cisD9,12,15 a-linonenic acid20:4cisD5,8,11,14 arachidonic acid

Double bonds in fatty acids usually have the cis configuration. Most naturally occurring fatty acids have an even number of carbon atoms.

CO

O-12

34a

bg

fatty acid with a cis-D9 double bond

ComparingMeltingPoints of SomeFattyAcids

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Effects of Double Bonds on the Melting Points

16:0 6016:1 118:0 6318:1 1618:2 -518:3 -1120:0 75

Fatty. Acids. Melting point. P. (0C)

20:4 -50

Melting Points of Fatty Acids and Solubility in Water

Solubility in H O

Chain Length

2

Melting Point

Mel

ting

poin

t

H2O

LearningCheck

Assignthemeltingpointsof–17°C,13°C,and69°Ctothecorrectfattyacid.Explain.

stearicacid(18C) saturatedoleicacid(18C) onedoublebondlinoleicacid(18C) twodoublebonds

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Solution

Stearicacidissaturatedandwouldhaveahighermeltingpointthantheunsaturatedfattyacids.Becauselinoleichastwodoublebonds,itwouldhavealowermpthanoleicacid,whichhasonedoublebond.

stearicacidmp69°Csaturatedoleicacidmp13°C

linoleicacidmp-17°Cmostunsaturated

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Omega-6andOmega3- FattyAcids

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Fatty acids § In vegetable oils are mostly omega-6 with

the first C=C at C6.linoleic acid CH3─(CH2)4─CH=CH─CH2─CH=CH─(CH2)7─COOH

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§ In fish oils are mostly omega-3 with the first C=C at C3.linolenic acidCH3─CH2─(CH=CH─CH2)3─(CH2)6─COOH

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SomeOmega-6andOmega-3FattyAcids

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LearningCheck

Writeafattyacidwith10carbonatomsthatis:

A.saturated

B.monounsaturatedomega-3

C.monounsaturatedomega-6

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Solution

Writeafattyacidwith10carbonatomsthatis:A.saturatedCH3—CH2—CH2—CH2—CH2—CH2—CH2—CH2—CH2—COOH

B.monounsaturatedomega-3CH3—CH2—CH=CH—CH2—CH2—CH2—CH2—CH2—COOH

C.monounsaturatedomega-6CH3—CH2—CH2—CH2—CH2—CH=CH—CH2—CH2—COOH

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Lipids

FatsandOils

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FatsandOils:Triacylglycerols

Fatsandoils are• Alsocalledtriacylglycerols (TG).• Estersofglycerol.• Producedbyesterification.• FormedwhenOHgroupsofglycerolreactwiththeCOOHofF.AsandliberateH2O

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Fats

Fats are mostly Triglycerides (TG):

Solid

FormationofaTriacylglycerolglycerol+threefattyacidstriacylglycerol

OHCH2

OH

OHCH2

CHO

(CH2)14CH3CHO

O(CH2)14CH3CHO

O(CH2)14CH3CHO

OOC (CH2)14CH3

CH OOC (CH2)14CH3

CH2 OOC (CH2)14CH3

CH2

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+ 3H2O

+

Triacylglycerols

Inatriacylglycerol,• Glycerolformsesterbondswiththreefattyacids.

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GlycerophospholipidsGlycerophospholipids (phosphoglycerides):-commonconstituentsofcellularmembranes.-Theyhaveaglycerol backbone.-HydroxylsatC1 &C2 areesterifiedtofattyacids.

C OHH

CH2OH

CH2OH

glycerol

An ester forms when a hydroxyl reacts with a carboxylic acid, with loss of H2O.

Formation of an ester:

O O

R'OH + HO-C-R" R'-O-C-R'' + H2O

Glycerides

Monoglyceride (a - monostearin) Diglyceride (a, a' - distearin)

H2C OH

HC OH

H2C OOC (CH2)16 CH3

H2C O

HC OH

H2C OOC (CH2)16 CH3

C (CH2)16 CH3

O

Triglyceride (b - palmityl distearin)

H2C O

HC O

H2C OOC (CH2)16 CH3

C (CH2)16 CH3

O

OC (CH2)14 CH3

( C18 )

(C16 )

(C18 )

Oils

Oliveoil• Containsahighpercentageofoleicacid,whichisamonounsaturatedfattyacidwithonecisdoublebond.

(TG+3Oleicacid)Liquid

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Unsaturated fatty acid chains have kinks that do not allow close packing.

LearningCheck

Whatarethefattyacidsinthefollowingtriacylglycerol?

(CH2)12CH3

OC

CH(CH2)7CH3(CH2)7CHOC

O(CH2)16CH3C

O

O

OCH2

CH2

CH

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Solution

(CH2)12CH3

OC

CH(CH2)7CH3(CH2)7CHOC

O(CH2)16CH3C

O

O

OCH2

CH2

CH

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Stearic acid

Oleic acid

Myristic acid

MELTING POINTS OF TRIGLYCERIDES

C6 -15

C12 15

C14 33

C16 45

C18 55

C18:1 (cis) -32

Triglyceride Melting Point (°C)

C18:1 (trans) 15

MeltingPointsofFatsandOils

Atriacylglycerolthatisafat• Issolidatroomtemperature.• Isprevalentinmeats,wholemilk,butter,andcheese.

Atriacylglycerolthatisanoil• Isliquidatroomtemperature.• Isprevalentinplantssuchasoliveandsafflower.

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OilswithUnsaturatedFattyAcids

Oils• Havemoreunsaturatedfats.• Havecisdoublebondsthatcause“kinks”inthefattyacidchains.

• Cannotpacktriacylglycerolmoleculesasclosetogetherasinfats.

• Havelowermeltingpointsthansaturatedfats.• Areliquidsatroomtemperature.

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SaturatedandUnsaturatedFattyAcidsInFatsandOils

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WaxesWaxes are• Estersofsaturatedfattyacidsandlong-chainalcohols.• Coatingsthatpreventlossofwaterbyleavesofplants.

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LipidsPhospholipids

&Glcerophospholipids

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Glycerol

PO4Amino alcohol

Fatty acid

Fatty acid

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PhospholipidsPhospholipids are the major component of all cell membranes.Phospholipid = two hydrophobic F.As "tails" + a hydrophilic"head" which is consisting of a phosphate group.-They can form lipid bilayers because of their amphiphiliccharacteristic.

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Glycerophospholipids (GPL)Glycerophospholipids (GPL)arepolar:• Themostabundantlipidsincellmembranes.• GPL=twochainsoffattyacids+phosphate+anaminoalcohol.

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Glycerol

PO4Amino alcohol

Fatty acid

Fatty acid

StructureandPolarityofAGlycerophospholipid

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GlycerophospholipidsGlycerophospholipids arepolar:

• ThepolaraminoalcoholareethanolamineorcholineandSer

CH3│++

HO−CH2−CH2−N−CH3 HO−CH2−CH2−NH3│

cholineCH3 ethanolamine+NH3│Aminoalcohols

HO−CH2−CH−COO−serine

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O

O

H2C O C RO

R C O CH

H2C O P O CH2 CH2 N+ CH3

CH3

CH3

O_Phosphatidic Acid Choline

Glycerophospholipids

LecithinandCephalin

Lecithin andcephalin areglycerophospholipids• Abundantinbrainandnervetissues.• Foundineggyolk,wheatgerm,andyeast.

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Examplesofglycerophospholipids

LipidsSphingolipids

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SphingolipidsSphingolipids• Aresimilartophospholipids.• Containsphingosine (along-chainaminoalcohol)+afattyacid+phosphate+asmallaminoalcohol.

• Havepolarandnonpolarregions.

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sphingosine

PO4amino alcohol

fatty acid

Sphingosine

Sphingosineisalong-chainunsaturatedaminoalcohol.

CH3−(CH2)12−CH=CH−CH−OH│CH−NH2│CH2−OH

Sphingosine

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Link to F.As

Link to phosphate + amino alcohol

SphingolipidsInsphingomyelin,asphingolipidfoundinnervecells• Thereisanamidebondbetweenafattyacidandsphingosine,an18-carbonalcohol.

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Glycosphingolipids• Glycosphingolipidscontainmonosaccharidesbondedtothe–OHofsphingosinebyaglycosidic bond.

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GlycosphingolipidsandCerebrosidesGlycosphingolipids.• Canbeacerebroside whenlinkedwithgalactose.

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StructuresofLipids

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