1711607810537_3- Amino Acids.ppt56tyyyyy

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1. Amino Acids
AminoAcidsarethebuildingunitsofproteins.Proteinsare
polymersofaminoacidslinkedtogetherbywhatiscalled“
Peptidebond”.
Thereareabout300aminoacidsoccurinnature.Only20
ofthemoccurinproteins.(Standardaminoacids)

2. AminoAcidsarenamedmostlyonthebasisoftheirsources.(trivial
names)
Asparaginewasfirstfoundinasparagus,andglutamateinwheat
(gluten).
Naming and numbering of amino acids

3. Eachaminoacidhas4differentgroupsattachedtoα-
carbon(whichisC-atomnexttoCOOH).These4groups
are:
Aminogroup
COOHgroup
Hydrogenatomandside
Chain(R)
R
Amino acids differs in terms of “R” group.
This group affect the nature, solubility and interactions of amino acids.
Structure of amino acids

5. Chiral carbon/asymmetric center
Ifacarbonatomisbondedtofourdifferentgroupsitiscalledasthe
asymmetricorchiralcarbon.
Theα-carbonofaminoacidsisattachedtofourdifferentchemical
groupsisachiraloropticallyactivecarbonatom.
Glycineistheexception.
Chiral carbon Achiral carbon
Optical properties of amino acids

6. Stereoisomers
Chiralcarboncanrotatetheplanepolarizedlightintotwo
directionseitherinrightortoleftdirectionandgenerate
stereoisomers.
Thoseaminoacidswhichrotateplanepolarizedlightin
rightdirectionarecalleddextro-rotatory,dextro=right
(D)andthoserotatinglightinleftarelevo-rotatory,levo=
left(L).

7. How to write the structure of D and L amino acids???
Thereferencestructureisglyceraldehyde.
Almost all amino acids in human body exist in L-configuration

8. Enantiomers
Thestereoisomerswhicharenon-superimposablemirror
imagesofeachotherarecalledenantiomers.
DandLformsoftheaminoacidsareenantiomers.
Chiral carbon
Optical rotation
Stereoisomers
Non-superimposable mirror images

14. Of20aminoacidstwoaminoacidshavesulfurinsidechain
Cysteine and Methionine.
What is cystine?
Only Cysteine form disulfide bonds methionine cannot.

16. Some features of neutral amino acids
Onlyoneaminoacidhasachiralalphacarbon
Glycine
NeutralSulfurcontainingaminoacids:
Cysteine and Methionine. What is cystine?
Neutral,hydroxylgroupcontainingaminoacids:
Serine,TyrosineandThreonine
Amino acids with amide group in side chain:
They are amide forms of aspartate and glutamate in which side chain
COOH groups are amidated.

17. Amino acids with aromatic side chain
Phenylalanine:It’salanineinwhichonehydrogenofCH
3is
substitutedwithphenylgroup.Soit’scalled
phenylalanine
Tyrosine:
Tryptophan: indole ring
Prolineis an imino acid not amino acid

18. III-Classification on basis of nutritional value:
1-Essentialaminoacids:Theseaminoacidscan’tbeformedin
thebodyandso,itisessentialtobetakenindiet.Theirdeficiency
affectsgrowth,healthandproteinsynthesis.
2-Nonessentialaminoacids:Thesearetherestofaminoacids
thatareformedinthebodyinamountenoughforadultsand
children.Theyaretheremaining10aminoacids.
3-Conditionalyessentialorsemiessentialaminoacids:These
areformedinthebodybutnotinsufficientamountforbody
requirementsespeciallyinchildren.

19. Hydroxylysineandhydroxyproline,arefoundinthecollagen
andgelatinproteins.
γ-Carboxyglutamicacidisthepartofbloodclottingprotein
prothrombin.
N-methyllysineisaconstituentofmyosin.
Sone amino acids are not the part of proteins???
Ornithineandcitrullineactastheintermediatesintheurea
cycle
Uncommon amino acids

20. Simple monoamino monocarboxylic amino acid have weak
acidic and weak basic groups within a single molecule.
Some times side chain contain additional ionizable groups which
also act as acid and base.
Acid-Base properties of amino acids

21. Anyprotonatedspeciecandonateitsprotonifitispresent
inthesolutionwhosepHiseitherequaltothepKaor
greaterthanpKaofthatspecie.
•pKaisanequilibriumconstant.
•pHisanindicationofhydrogenioncontentina
solution

22. 22
Isoelectric point (pI)
The pH at which the amino acid exists largely in a neutral, zwitterionic
form (amphoteric molecule).
pI = 1/2 (pK
a1+ pKa
2)
For the simplest amino acid,, pKa1=2.34 and pK
a2=
9.6, pI= 5.97

23. Titration curve of monoamine and monocarboxylic acid
amino acid
AcidcandonateprotonwhenpHof
systembecomesequaltoorgreaterthan
pKaofacid.
pKaof–COOH=2.34
pKaof–NH3+=9.60

26. Titration curve of amino acids having acidic side chain
pK1of–COOH=2.19
pK2of–NH3+=9.67
pKr(sidechain-COOH)=4.25

27. pI =
pKa
1+ pKa
3
2
pI = 2.7
Isoelectric point (pI) of acidic amino acids

28. Titration curve of amino acids having basic side chain
pK1of–COOH=1.82
pK2of–NH3+=9.17
pKr(sidechain-NH)=6.0

29. pI =
pKa
2+ pKa
3
2
pI = 9.7
Isoelectric point (pI) of basic amino acids

30. Can exist as a positive ion if the solution is more acidic than its pI
Can exist as a negative ion if the solution is more basic than its pI

31. ACIDIC AND BASIC PROPERTIES OF AMINO
ACIDS
•Amino acids in aqueous solution contain weakly
acidic α-carboxyl groups and weakly basic α-amino
groups.
•Thus can act as buffers.
•pH = pK
a+ log [A-]/[HA]