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acids
AtifHKhirelsied,BSc,MSc,PhD.
DepartmentofBiochemistry
InternationalUniversityofAfrica,Khartoum,Sudan
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Leucine
Aspartate
Lysine Cysteine
Phenylalanine u ama e Glutamine
Tryptophan
yc ne
Proline
Histidine
er ne
Tyrosine
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Biological importance of amino acids
Biosynthesisofbodyproteins.
Biosynthesisofnonproteinsnitrogenouscompounds.
.
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Sources of amino acid pool Dietaryproteins.
.
.
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Non-essential amino acids Haveshortsyntheticpathways.
Formedbyamination ofmetabolicintermediates.
.
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Nutritional value of proteins
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NonessentialaminoacidsareformedbyTHREE generalmechanisms:
.
2. Assimilationoffreeammonia
3. Modificationofexistingaminoacids.
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Transamination
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Transamination
Requirespyridoxal phosphate(PLP).
PLPboundto alysineresidueintheactivesiteofthe
enzyme.
ItformsaSchiffbaseintermediatedurin thereaction.
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Glutamate synthesis Glutamte isformedbyreductiveamination
ofketo
glutarate catalyzedbyglutamatedehydrogenase enzyme.
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Glutamate synthesis Glutamte
canalsobesynthesizedbytransamination reaction.
COO
|
=
COO
|
CHNH +Amino ketoacid acid
|CH2
|CH2
CH2
|
CH2|
COO
ketoglutarate Glutamate
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Glutamine synthesis
amidation ofglutamate.
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Alanine synthesisorma ono a an ne y ransam na on o pyruva e,ca a
yze
byalanine transaminase.
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Aspartate synthesis
Aspartateissynthesizedbytransaminationofoxaloacetate
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Asparagine synthesis As artate is formed b amidation of as
artate catal zed b
asparagine synthetase.
COOCOO
CHNH3+
|Glutamine Glutamate |CHNH3
+
2
|
COO
ATP AMP+PPi
CH2|
Aspartate Asparagine
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Serine synthesisSerineiss nthesizedb thetransaminationand
dephosphorylation of3phosphogylcerate.
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Glycine synthesis Serinehydroxymethyltransferase
cansynthesize
l cine from serine
Serinehydroxymethyltransferase
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Glycine synthesis
1. Choline dehydrogenase,1
. ,
3. Betainehomocysteine N2
,
4. Sarcosine demethylase
5. Sarcosine oxi ase,. 3
4
5
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Glycine synthesis Intheliver
cytosol glycine transaminase canuseglyoxylate
andglutamatetoformglycine.
N5,N10CH2H4folate to formglycine fromCO2 andNH4
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Tyrosine synthesis
Phenylalaninehydroxylase
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Tyrosinesynthesis
Isformedfromphenylalanineinareactioncatalyzedbyphenylalaninehydroxylase.
Thereactionusestetrahydrobiopterin asprotondonor
Phen lalanineh drox lase isamixedfunctionox enase
presentinliver.
Deficiencyoftheenzyme orthecofactorcauses
phenylketonuria.
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Phenylketonuria
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Cysteine synthesis
Cysteinecontainsatomsdonatedby
o me on ne an ser ne.
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Cysteine synthesis
Cysteinecontainsatoms
ona e y o
methionine andserine.
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Proline isformedfromglutamate
ProlineDehydrogenase
ProlineDehydrogenase
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Hydroxyproline andhydroxlysine
Princi all found in colla en
lysinebyprolyl andlysyl hydroxylase.
Theenzymesarepeptideshydroxylases requiremolecular
,
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Selenocysteine
Selenocyteine arisescotranslational modificationof
serine.
Ispresentintheactivesiteofseveralenzymesincluding;
Thioredoxin reductase
Glutathione eroxidase
Deiodinase
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Selenocysteine
ThetRNAsec isfirstchargedwithserine byserine
amionacyltransferase
Subsequentlytheserineoxygenisreplacedwith
selenium
Seleniumisintroducedasselenophosphate formedby
selenophosphate synthase.
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Valine leucine andisoleucine
Canbesynthesizedbytransamination oftheirrespective
keto acids
Thusvaline,leucine andisoleucine aredietaryessential
aminoacids,butcanbereplacedby ketoisovalarate,
ketomethylvalarate and ketoisocaproate respectively
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Histidine andarginine
Histidine andarginine aresemiessential.
nutritionallyessentialforchildren
Histidine isrequiredforthenormalgrowthoflongbones
A summary of pathways involved
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Asummaryofpathwaysinvolved
inthesynthesisofnonessential
.
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