MacromoleculesMacromoleculesBIOL222

Ch.5

Overview:TheMoleculesofLifeOverview:TheMoleculesofLife

• Macromolecules

• largemoleculescomposedofthousandsofcovalentlyconnectedatoms

• Builtfromcarbonbackbone

• AlsocontainlargenumbersofHandO

• fourclasses:

• Carbohydrates

• Lipids

• Proteins

• Nucleicacids

MacromoleculesMacromolecules

• Polymer

• longmoleculeconsisEngofmanysimilarsubunits

• Monomers

• Buildingblocksofpolymers

• Threeofthefourclassesofmacromoleculesarepolymers:

• Carbohydrates

• Proteins

• Nucleicacids

• dehydra9onsynthesis(condensa9onreac9on)

• occurswhentwomonomersbondtogether

• throughthelossofawatermolecule

• hydrolysis

• Processofbreakingpolymersdowntomonomers

• essenEallythereverseofthedehydraEonreacEon

TheSynthesisandBreakdownofPolymersTheSynthesisandBreakdownofPolymers

Fig.5‐2Fig.5‐2

Short polymer

HO 1 2 3 H HO H

Unlinked monomer

Dehydration removes a watermolecule, forming a new bond

HO

H2O

H1 2 3 4

Longer polymer

(a) Dehydration reaction in the synthesis of a polymer

HO 1 2 3 4 H

H2OHydrolysis adds a watermolecule, breaking a bond

HO HH HO1 2 3

(b) Hydrolysis of a polymer

TheDiversityofPolymersTheDiversityofPolymers

2 3 HOH

• cellsholdthousandsofdifferentkindsof

macromolecules

• Humanscanmakeupto150,000different

proteins

• Macromoleculardiversity

• indicaEveofbiologicaldiversity

• varietyofpossiblepolymersvirtuallylimitless

• fromasmallsetofmonomers

Carbohydrates:fuelandbuildingmaterialCarbohydrates:fuelandbuildingmaterial

• Carbohydrates

• Polymersofsimplesugarmonomers

• Monosaccharides

• Polysaccharides

• Carbohydratemacromolecules

• Builtofmonosacharides

SimpleSugarsSimpleSugars

• Monosaccharides

• Typically(CH2O)n

• Glucose(C6H12O6)

• mostcommonmonosaccharide

• Monosaccharidesclassifiedby

• LocaEonofthecarbonylgroup(C=O,asaldoseorketose)

• Numberofcarbonsinthecarbonskeleton

Fig.5‐3Fig.5‐3

Dihydroxyacetone

Ribulose

Ket

oses

Ald

oses

Fructose

Glyceraldehyde

RiboseGlucose Galactose

Hexoses (C6H12O6)Pentoses (C5H10O5)Trioses (C3H6O3)

• OVendrawnaslinearskeletons

• manysugarsformringsinaqueoussoluEons

• Monosaccharides

• majorfuelforcells

• Glucose

• rawmaterialforbuildingmolecules

• CarbonskeletonsforaminoacidsandfaYyacids

SimpleSugarsSimpleSugars

Fig.5‐4Fig.5‐4

(a) Linear and ring forms (b) Abbreviated ring structure

• Disaccharide

• twomonosaccharides

• JoinedbydehydraEonsynthesis

• glycosidiclinkage

• covalentbondbetween1CofonemonosaccharideandOon4C

ofnextmonosaccharide

PolysaccharidesPolysaccharides

Fig.5‐5Fig.5‐5

(b) Dehydration reaction in the synthesis of sucroseGlucose Fructose Sucrose

MaltoseGlucoseGlucose(a) Dehydration reaction in the synthesis of maltose

1–4glycosidic

linkage

1–2glycosidic

linkage

PolysaccharidesPolysaccharides

• Polysaccharides

• polymersofsugars

• storageandstructuralroles

• structureandfuncEon

• determinedbymonomersandposiEonsofglycosidiclinkages

StoragePolysaccharidesStoragePolysaccharides

• Starch

• storagepolysaccharideofplants

• asgranuleswithinchloroplastsandotherplasEds

• consistsenErelyofglucosemonomers

• maybethousandsofmonomerslong

Fig.5‐6Fig.5‐6

(b) Glycogen: an animal polysaccharide

Starch

GlycogenAmylose

Chloroplast

(a) Starch: a plant polysaccharide

Amylopectin

Mitochondria Glycogen granules

0.5 µm

1 µm

• Glycogen

• storagepolysaccharideinanimals

• Humansandothervertebratesstoreglycogenmainlyinliverand

musclecells

StoragePolysaccharidesStoragePolysaccharides

Fig.5‐6Fig.5‐6

(b) Glycogen: an animal polysaccharide

Starch

GlycogenAmylose

Chloroplast

(a) Starch: a plant polysaccharide

Amylopectin

Mitochondria Glycogen granules

0.5 µm

1 µm

StructuralPolysaccharidesStructuralPolysaccharides

• Cellulose

• Polysaccharide

• majorcomponentofplantcellwalls

• alsopolymerofglucose

• glycosidiclinkagesdiffer

• Thedifferenceisbasedontworingformsforglucose:alpha(α)and

beta(β)

Fig.5‐7Fig.5‐7

(a) α and β glucose ring structures

α Glucose β Glucose

(b) Starch: 1–4 linkage of α glucose monomers (b) Cellulose: 1–4 linkage of β glucose monomers

• αglucose

• Polymersarehelical

• Starch,glycogen

• βglucose

• Polymersarestraight

• Cellulose,chiEn

• InstraightstructuresHatomsononestrand

• canbondwithOHgroupsonotherstrands

• Parallelcellulosemoleculesheldtogetherthiswayaregrouped

intomicrofibrils

• whichformstrongbuildingmaterialsforplants

StructuralPolysaccharidesStructuralPolysaccharides

Fig.5‐8Fig.5‐8

β Glucosemonomer

Cellulosemolecules

Microfibril

Cellulosemicrofibrilsin a plantcell wall

0.5 µm

10 µm

Cell walls

• Enzymesthatdigeststarchbyhydrolyzingαlinkagescan’thydrolyzeβ

linkagesincellulose

• αamylase

• CelluloseinhumanfoodpassesthroughthedigesEvetractas

insolublefiber

• Somemicrobesuseenzymestodigestcellulose

• cellulase

• Manyherbivores,fromcowstotermites,havesymbioEc

relaEonshipswiththesemicrobes

StructuralPolysaccharidesStructuralPolysaccharides

• Chi9n

• structuralpolysaccharide

• exoskeletonofarthropods

• structuralsupportforthecellwallsofmanyfungi

StructuralPolysaccharidesStructuralPolysaccharides

Fig.5‐10Fig.5‐10

The structureof the chitinmonomer.

(a) (b) (c)Chitin forms theexoskeleton ofarthropods.

Chitin is used to makea strong and flexiblesurgical thread.

Lipids:diversegroupofhydrophobicmoleculesLipids:diversegroupofhydrophobicmolecules

• Lipids

• onlymacromoleculesthatdonotformpolymers

• unifyingfeatureoflipidsishavingliYleornoaffinityforwater

• hydrophobic

• consistmostlyofhydrocarbons

• nonpolarcovalentbonds

• Themostbiologicallyimportantlipidsarefats,phospholipids,and

steroids

LipidsLipids

• Fats

• constructedfromtwotypesofsmallermolecules

• Glycerol

• faYyacids

• Glycerol

• three‐carbonalcoholwithahydroxylgroupaYachedtoeachcarbon

• faGyacid

• acarboxylgroupaYachedtoalongcarbonskeleton

Fig.5‐11Fig.5‐11

Fatty acid(palmitic acid)

Glycerol(a) Dehydration reaction in the synthesis of a fat

Ester linkage

(b) Fat molecule (triacylglycerol)(triglyceride)

• Fatsseparatefromwater

• becausewatermoleculesformhydrogenbondswitheach

otherandexcludethefats

• Triacylglycerol(triglyceride)

• threefaYyacidsjoinedtoglycerolbyesterlinkages

• combingacidwithanalcohol

• faYyacidandglycerol

FatsFats

• FaYyacids

• varyinlength(numberofcarbons)

• andinthenumberandlocaEonsofdoublebonds

• SaturatedfaGyacids

• maximumnumberofhydrogenatomspossible

• nodoublebonds

• UnsaturatedfaGyacids

• oneormoredoublebonds

FaGyAcidsFaGyAcids

• saturatedfats

• FatsmadefromsaturatedfaYyacids

• solidatroomtemperature

• Mostanimalfatsaresaturated

• unsaturatedfatsoroils

• FatsmadefromunsaturatedfaYyacids

• liquidatroomtemperature

• Plantfatsandfishfatsareusuallyunsaturated

FaGyAcidsFaGyAcids

Fig.5‐12Fig.5‐12

Structuralformula of asaturated fatmolecule

Stearic acid, asaturated fattyacid(a) Saturated fat

Structural formulaof an unsaturatedfat molecule

Oleic acid, anunsaturatedfatty acid

(b) Unsaturated fat

cis doublebond causesbending

PhospholipidsPhospholipids

• Phospholipid

• twofaYyacidsandaphosphategroupaYachedtoglycerol

• faYyacidtailsarehydrophobic

• phosphategroupanditsaYachmentsformahydrophilichead

• Amphipathic

• Bothhydrophobicandhydrophilicregions

Fig.5‐13Fig.5‐13

(b) Space-filling model(a) (c)Structural formula Phospholipid symbol

Fatty acids

Hydrophilichead

Hydrophobictails

Choline

Phosphate

Glycerol

Hyd

roph

obic

tails

Hyd

roph

ilic

head

• Phospholipidbilayer

• Phospholipidsaddedtowater

• self‐assembleintoabilayer

• withthehydrophobictailspoinEngtowardtheinterior

• Phospholipidsarethemajorcomponentofallcellmembranes

AppliedPhospholipidsAppliedPhospholipids

Fig.5‐14Fig.5‐14

Hydrophilichead

Hydrophobictail WATER

WATER