Dr Gayathri G Nair ,Sree Gokulam medical college. Amino Acids Physical properties

1. 1Dr GayathriG Nair

2.  SOLUBLE
 polar solvents
 Water
 alcohol
 INSOLUBLE
 (non-polar solvents)
 benzene
2Dr GayathriG Nair

3.  Sweet:-
 Bitter:-
 Tasteless:-Leucine
3
Glycine, Alanine,Valine, Serine
tryptophan, histidine and proline
Isoleucine and arginine
Dr GayathriG Nair

4.  Melting point:
 all amino acids have high melting points
more than 2000 c
 ABSORBS ULTRAVIOLET LIGHT:The
aromatic amino acids viz tryptophan,
tyrosine ,phenylalanine and histidine.
4Dr GayathriG Nair

5.  Amino acids having asymmetric carbon atom
exhibit optical activity
 Asymmetry arises when 4 different groups
are attached to the same carbon atom
Glycine is the simplest
amino acids with no
asymmetric carbon
atom and optically
inactive
5Dr GayathriG Nair

6.  The mirror image forms
produced with reference
to alpha carbon atom are
called D & L isomers
 L-AA occur in nature
therefore are called
natural amino acids
 D-AA seen in small
amounts in micro
organisms and as
constituents of certain
antibiotics .
6Dr GayathriG Nair

7.  All amino acids have acidic(carboxyl ) and basic (amino)
group
 Acid –base behaviour : the carboxyl group of an amino
acid can donate one proton (H+ ) and behave as an acid
forming an negatively charged anion
 Similiarly amino group can accept a proton and behave
as base forming positively charged cation
 Substances having two way property are called
ampholytes or amphoteric
 Amino acids have both acidic and basic groups and are
amphoteric in nature
7Dr GayathriG Nair

8.  Zwitter in german means hybrid
 At physiological pH;
 The carboxyl group exists as carboxylate ion
coo-
 And amino group is in the protonated form
NH3+
 Mono amino mono carboxylic acids exist in
aqueous solution as dipolar or zwitter ion
 which means that they have both positive and
negative charges on the same amino acids
 The overall molecule is electrically neutral
8Dr GayathriG Nair

9.  Definition:Thus the molecular species which
contain equal number of ionizable group of
opposite charge and as a result bear no net
charge are zwitter ion
 As amino acids are both a proton donor and a
proton acceptor it is an ampholyte
9Dr GayathriG Nair

10.  The pH at which the molecules carry no net
charge is known as isoelectric point or
isoelectric pH
 The amino acids at its isoelectric pH does not
move in electric field as it carries no net charge
10Dr GayathriG Nair

11.  Amino acids exerts chemical properties
because of their
 Carboxyl group
 Amino group
 Side chain ‘R’
 All amino acids contain first two groups and
hence undergo chemical reaction
characteristic for these group
11Dr GayathriG Nair

12. Reactions Answered by group
Biuret reaction Nitrogen in Peptide bonds
Ninhydrin Alpha amino group
Xanthoproteic test Benzene ring(phe,tyr,trp)
Millons test phenol(tyrosine)
Aldehyde test Indole (tryptophan)
Sakaguchi test Guanidinium (arginine)
Sulphur test Sulfhydryl (cysteine)
Pauly’s test Imidazole (histidine)
12Dr GayathriG Nair

13. Physical properties
 Soluble ,taste,melting
 Optical property
 Ionising property
 Isoelectric pH
Chemical properties
 Colour reaction
13Dr GayathriG Nair

14. 14Dr GayathriG Nair

15.  Some of the biologically active oligopeptides
are:
1. THYROTROPIN RELEASING HORMONE
(TRH) is a tripeptide
 Hormone secreted from hypothalamus
 stimulate pituitary gland to releaseTSH
15Dr GayathriG Nair

16. 2. GLUTATHIONE:Tripeptide,found in all
mammalian cell except neurons with the
sequence of glu-cys-gly
 Found in all mammalian cells except
neurons
 Maintains RBC membrane integrity
 Involved in detoxification mechanism
 Transport of aa across the cell membrane.
16Dr GayathriG Nair

17. 3. Oxytocin: It’s a nano peptide (9 AA), a
hormone of posterior pituitary gland
 Function: contraction of uterus
17Dr GayathriG Nair

18. 4. Vasopressin/antidiuretic hormone:
 Nanopeptide
 It is secreted from posterior pituitary gland
 Function: retention of water from renal
tubules. Increases BP
18Dr GayathriG Nair

19. 5. Angiotensin:
 Angiotensin I is a decapeptide
 Angiotensin II is a octapeptide, vasoconstrictor
 Functions:
1) Raises blood pressure by stimulation of
adrenal gland
2) Release of aldosterone that promote sodium
retention
19Dr GayathriG Nair

20. 6. Bradykinin :Nanopeptide,
 Powerful vasodilator and causes contraction
of smooth muscle
 Responsible for producing peripheral and
visceral pain by stimulating pain receptors
 Mediates production of Pg’n E2 from
arterial walls
7. Kallidin: Decapeptide, vasodilator
20Dr GayathriG Nair

21. 8. Methionine encephalins:
 Pentapeptide found in brain
 Binds to receptors in certain cells of brain
and induce analgesia (decreases pain
sensations)
9. Aspartame:
 Commercially synthesized ,
 Dipeptide (aspartic acid + phenylalaninie)
 Its an artificial sweetner
 Unsuitable for phenyl ketonurics
21Dr GayathriG Nair

22. 10. Antibiotics:Gramicidin S
 An antibiotic produced by bacillus brevis
 Decapeptide
 It contains D-phenylalanine,
11.CARNOSINEAND ANSERINE: Dipeptide with
sequence beta-Alaninie+ Histidine
 Carnosine stimulates muscle contraction
and it is methylated to form anserine
 both are present in skeletal muscle
22Dr GayathriG Nair

23.  Hormones:TRH,OXYTOCIN,VASOPRESSIN
ANGIOTENSIN I / II
 GLUTATHIONE
 BRADYKININ
 KALLIDIN
 CARNOSINE/ANSERINE
 ANTIBIOTICS
 ASPARTAME
23Dr GayathriG Nair