3. haemoglobin structure and function

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HAEMOGLOBIN STRUCTURE AND FUNCTION

Haemoglobin is a tetramer

Compose o! " pol#peptie $%ains &2

an '

an " %aem gro(ps

Ea$% globin $%ain is atta$%e to a %aem gro(p

Str($t(re o! %aemoglobin

Hig%l# $omple) an *ie+e at " le*els

,RIMAR- STRUCTURE

Se.(en$e o! amino a$is in t%e pol#pepties t%at $onstit(te t%e globin $%ain

SECONDAR- STRUCTURE

Heli$al $on!ormation o! t%e pol#peptie $%ain

T%ere are / %eli$al segements esignate !rom A0H

Iron o! %aem is bo(n to %istiine at t%e / t%position o! F %eli$al segement

TERTIAR- STRUCTURE

Re!ers to t%e t%ree imensional arrangement o! t%e $oile globin $%ain an %as a

%aem $ontaining po$1et bet+een t%e E0 H %eli$es

2UATERNAR- STRUCTURE

Relations%ip bet+een t%e !o(r globin $%ains

Bons bet+een pol#peptie $%ains allo+ !or $%ains to slie on ea$% ot%er an at

same time maintain stabilit#

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STRUCTURE OF HAEM

Ea$% %eme mole$(le $onsists o! protoporp%#rin +it% an iron &Fe334

,rotoporp%#rin is a tetrap#rrole +%i$% is a $omple) str($t(re mae (p o! "

p#rrole rings

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Heme is s#nt%esi5e !rom gl#$ine an s($$#nl Co A

T%e !irst step is $onensation o! Gl#$ine an s($$#nl CoA to !orm

amino

lae*(lani$ a$i +it% t%e %elp o! en5#me aminolae*(lini$ a$i s#nt%etase6 T%is

step ta1es pla$e in t%e mito$%onrion6

aminolae*(lini$ a$i mo*es into t%e $#tosol

T+o mole$(les o!

aminole*(lini$ a$i $ombine to !orm porp%obilinogen

Fo(r mole$(les o! porp%obilinogen in t(rn $ombine to !orm (roporp%#rinogen III

Utop%orp%#rinogen III is t%en moi!ie in t+o !(rt%er steps to !orm

Coprop%orp%inogen III6

Coprop%or%inogen III enters t%e mito$%onrion +%ere it is $on*erte to

,rotoporp%#rin6

T%e !inal stage is $ombination o! !erro(s &Fe'34 to !orm %aem6

Globin $%ain s#nt%esis is (ner t%e $ontrol o! genes lo$ate on $%romosomes 77

&

$%ains4 an $%romosome 78 &

$%ains46 S#nt%esis in t%e $#toplasm on

ribosomes6

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Haemoglobin *ariants

9ariants o! %aemoglobin in$l(e Haemoglobin A: A': F: Go+er I: Go+er II an

,ortlan

A(lts Hb A ;= an Hb F ?6>=

Ne+borns HbF /?= an Hb A '?=

Hb A is t%e prin$ipal %aemoglobin o! a(lts 7 pair o! alp%a &

$%ains an one

pairs o! beta &

$%ains22

Foetal %aemoglobin &Hb F4 is t%e preominant %aemoglobin in !oetal li!e an

$ontains a pair o! alp%a &

an a pair o! gamma &

$%ains

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Abnormal %aemoglobins

O*er @>? abnormal %aemoglobins %a*e been es$ribe

Si$1le $ell %aemoglobin s(bstit(tion o! gl(tami$ a$i b# *aline on position 8 o!

t%e

$%ain6

T%alassemia e!e$ti*e pro($tion o! alp%a or beta $%ains6

Haemoglobin F(n$tion

Re $ells $arr# o)#gen !rom t%e l(ngs to t%e tiss(es an $arbon io)ie !rom

tiss(es to l(ngs

As t%e %aemoglobin mole$(le loas an (nloas o)#gen t%e ini*i(al globin

$%ains in t%e %aemoglobin mole$(le mo*e on ea$% ot%er

%en o)#gen is (nloae t%e

$%ains are p(lle apart permitting entr# o! t%e

metabolite ':@ Dip%osp%ogl#$erate &':@ D,G4 res(lting in lo+er a!!init# o! t%e

mole$(le !or o)#gen

T%is mo*ement is responsible !or t%e sigmoi !orm o! t%e %aemoglobin o)#gen

isso$iation $(r*e6

T%e ,>?&partial press(re at +%i$% o)#gen is %al! sat(rate +it% o)#gen4 o! normal

bloo is '868 mmHg

it% in$rease a!!init# !or o)#gen t%e $(r*e s%i!ts to t%e le!t &,>? !alls4

it% e$rease a!!init# &,>?rises4

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3. haemoglobin structure and function

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