2013 Topic 2.2 Protein Lecture Notes

8/19/2019 2013 Topic 2.2 Protein Lecture Notes

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Oligoprotein = 4-10 amino acid residues

Amino Acid Peptide Protein

No. of Amino Acid

1 2-50 >50

MolecularWeig t

!5"000 #"000 $40"000"000


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2

%roteins 1

& %roteins are 'iopol(mers of -amino acids 'ecauset e amino group is 'onded to t e α car'on atom"ne)t to t e car'on(l group.

& * e p (sical and c emical properties of a protein aredetermined '( its constituent amino acids .

& * e indi+idual amino acid su'units are ,oined '(amide lin ages called peptide bonds .


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/tructure of %roteins


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4

%roteins 2

& %roteins are t e most a'undant organic molecules inanimals" pla(ing important roles in all aspects of cellstructure and function.

& ariet( of functionsstructureen (mes

transportprotection

ormones


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5

3)amples of %rotein unctions

Class of Protein Example Function of Example

/tructural proteins ollagen" eratin /trengt ens tendons"s in" air" nails

3n (mes 6NA pol(merase 7eplicates 8 repairs6NA

*ransport proteins 9emoglo'in *ransports O 2 to cells

%rotecti+e proteins Anti'odies omple) :it foreignproteins

9ormones ;nsulin 7egulates glucosemeta'olism


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#

Amino Acids

& -N9 2 on t e car'on ne)t to - OO9.

&


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/tandard Amino Acids 1

& *:ent( standard α -amino acids.

& 6iffer in side-c ain c aracteristics

-9 or al (lcontains an -O9contains sulfur contains a non'asic nitrogen

as - OO9as a 'asic nitrogen


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B

20 /tandard Amino Acids

non-polar, aliphatic residues

Glycine Gly G

GGU GGC GGA GGG

Alanine Ala A

GCU GCC GCA GCG

Valine Val V

GUU GUC GUA GUG

Leucine Leu L UUA UUG CUU CUC

CUA CUG


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C

/tandard Amino Acids 2& Neutral amino acids

Alanine Ala A?

Asparagine Asn N?(steine (s ?


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10

/tandard Amino Acids

& Acidic amino acids Aspartic acid Asp 6?


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11

1. Name

& aline& ;soleucine

& eucine

& Alanine&


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12

2. Name

& Asparagine&


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1

3ssential Amino Acids

& Arginine Arg?& * reonine * r?& (sine (s?& aline al?&

% en(lalanine % e?

& *r(ptop an *rp?& Met ionine Met?& 9istidine 9is?& eucine eu?

& ;soleucine ;le?

9umans are a'le to s(nt esi e onl( 10 of t e 20amino acids necessar( for protein s(nt esis. * eremaining 10 are called essential amino acidssince t e( must 'e o'tained from dietar( sources.

ailure to include an adeHuate dietar( suppl( oft ese essential amino acids can lead to se+eredeficienc( diseases.


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14

omplete %roteins

& %ro+ide all t e essential amino acids.

& 3)amples t ose in meat" fis " mil " eggs.

& %lant proteins are generall( incomplete.

& egetarians s ould eat man( different inds of plants" or supplement diet :it mil oreggs.


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15

& 4-9(dro)(proline" 5- (dro)(l(sine found in collagen.

& 6-


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1#

J:itterion

& Amino acid e)ists as a dipolar ion.& - OO9 loses 9 @" -N9 2 gains 9 @.

& Actual structure depends on p9.


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1

%roperties of Amino Acids

& 9ig melting points" o+er 200 ° .

& More solu'le in :ater t an in et er.

& arger dipole moments t an simple acids orsimple amines.

& ess acidic t an most car'o)(lic acids" less

'asic t an most amines.

H3 N CH

R

C

O

O+ _

pK a = 10 pK ' = 12


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1B

/tructure and p9


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1C

;soelectric %oint

& p9 at : ic amino acids e)ist as t e :itterionneutral?.

& 6epends on structure of t e side c ain.

& Acidic amino acids" isoelectric p9 K .

& Fasic amino acids" isoelectric p9 KC.

& Neutral amino acids" isoelectric p9 is slig tl( acidic"5-#.


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3lectrop oresis


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21

7educti+e Amination

& * is met od for s(nt esi ing amino acids is'iomimetic" mimics t e 'iological process.

& 7eact an α - etoacid :it ammonia" t en reduce

t e imine :it 9 2 L%d.& 7acemic mi)ture is o'tained.& Ise en (me catal(st to o'tain pure form.


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22

/(nt esis from α -9alo Acid

& 9ell- ol ard-Jelins ( reaction places Fr on t e α car'on of a car'o)(lic acid.

& Fromine is t en replaced '( reaction :it e)cessammonia.

& A racemic mi)ture is o'tained.


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2

/trec er /(nt esis

& irst no:n s(nt esis of amino acid" 1B50.

& Alde (de reaction :it N9 . (ields imine.& (anide ion attac s t e protonated imine.& 7esulting α -amino nitrile is (drol( ed to a

car'o)(lic acid.


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24

/trec er Mec anism

9(drol(sis of t e nitrile (ields t e amino acid.


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25

7esolution of Amino Acids

& Isuall(" onl( t e enantiomer is 'iologicall(acti+e.

& on+ert t e amino acid to a salt" using a c iralacid or 'ase. * e result is a mi)ture ofdiastereomeric salts : ic can 'e separated '(c romatograp (.

& Ise an en (me suc as ac(lase : ic :ill react:it onl( one enantiomer.


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2#

7eaction :it Nin (drin

& Ised to +isuali e spots or 'ands of amino acidsseparated '( c romatograp ( or electrop oresis.

& 6eep purple color formed :it traces of an(amino acid.


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2

/tructure of %eptide& * e peptide 'ond is an amide 'ond.& Amides are +er( sta'le and neutral.& or classification purpose" c ains :it fe:er t an

50 amino acids are often called peptides" : ile t eterm protein is used for larger c ains.


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2B

%eptide Fond ormation

& * e amino group of one molecule condenses :it t eacid group of anot er.& %ol(peptides usuall( a+e molecular :eig t less t an

5000.&

%rotein molecular :eig t #000-40"000"000.


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2C

Frad( inin

& An oligopeptide" four to ten amino acids.

& %eptide structures are dra:n :it t e N-terminal end at t e left.

& %eptides are named from left to rig t

argin(lprol(lprol(l arginine.


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0

Amino Acid omposition& /eparate t e indi+idual peptide c ains.& Foil :it # M 9 l for 24 ours.& /eparate in an amino acid anal( er.


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1

%artial 9(drol(sis

& Frea t e peptide c ain into smaller fragments.

& *r(psin clea+es at t e car'o)(l group of l(sineand arginine.

& (motr(psin clea+es at t e car'o)(l group ofp en(lalanine" t(rosine" and tr(ptop an.

& /eHuence eac fragment" t en fit t em toget erli e a ,igsa: pu le.


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2

. ist o: tr(psin :or s.

& lea+es at car'o)(l groups of l(sine andarginine.

& lea+es at car'o)(l groups of p en(lalanine"t(rosine" and tr(ptop an.

& lea+es at car'o)(l groups of +aline" alanine"leucine" and isoleucine.

& lea+es at car'o)(l groups of serine"c(steine" and met ionine.

lea+es at car'o)(l groups of l(sine and arginine.


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lassification of %roteins

& /imple (drol( e to amino acids onl(.

& on,ugated 'onded to a nonprotein group" suc assugar" nucleic acid" or lipid.

& i'rous long" string( filaments" insolu'le in :ater"function as structure. 3g. collagens" elastins"fi'rinogen" eratins" m(osins.

&


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4

lass of 3n (mesMain Class Some subclasses Type of reaction catalysed

9(drolases ipase 9(drol(sis of an ester groupNucleases 9(drol(sis of an p osp ate group

%roteases 9(drol(sis of an amide group

;somerase 3pimerases ;somerisation of a c iralit( center

igases ar'o)(lases Addition of O2

/(nt etases ormation of ne: 'ond

(ases 6ecar'o)(lases oss of O 26e (drases oss of 9 2O

O)idoreductases 6e (drogenases ;ntroduction of dou'le 'ond '(remo+al of 9 2

O)idases O)idation

7eductases 7eduction

*ransferases Ginases *ransfer of a p osp ate group


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5

lass of %roteinClass of Protein Example Function of Example

/tructuralproteins ollagen"eratin /trengt en tendons" s in" air"nails.

3n (mes 6NApol(merase

7eplicates and repairs 6NA.

*ransportproteins 9emoglo'in *ransport O2 to t e cells.

ontractileproteins

Actin"m(osin

ause contraction of muscles.

%rotecti+eproteins

Anti'odies omple) :it foreign proteins.

9ormones ;nsulin 7egulates glucose meta'olism.

*o)in /na e+enoms

;ncapacitate pre(.


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#

e+els of %rotein /tructure

& %rimar( t e seHuence of t e amino acids in t ec ain and t e disulfide lin s.

& /econdar( structure formed '( (drogen 'onding.3)amples are α - eli) and pleated s eet.

& *ertiar( complete -6 conformation.

& Duaternar( association of t:o or more peptidec ains to form protein.


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Alp a 9eli)3ac car'on(l o)(gen can (drogen 'ond :it an N-9

(drogen on t e ne)t turn of t e coil.


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B

%leated / eet3ac car'on(l o)(gen (drogen 'onds :it an N-9

(drogen on an ad,acent peptide c ain.

( f


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C

/ummar( of /tructure


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6enaturation

& 6isruption of t e normal structure of a protein"suc t at it loses 'iological acti+it(.

& Isuall( caused '( eat or c anges in p9.

& Isuall( irre+ersi'le. A coo ed egg cannot 'euncoo ed.

2013 Topic 2.2 Protein Lecture Notes

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