Amino acids are a set of 20 different molecules used to build
proteins. Proteins consist of one or more chains of amino acids called
polypeptides. The sequence of the amino acid chain causes the polypeptide to
fold into a shape that is biologically active. The amino acid sequences of
proteins are encoded in the genes.
 |
| Amino acids |
 |
| General Structure |
Central carbon (Cα)
attached to:
• Hydrogen (H)
• Amino group (-NH2)
• Carboxyl group (-COOH)
• Side chain (R)
20 Different Amino Acids
 |
| 20 Different amino acids |
1. Enantiomers: The
two non-super imposable mirror images. Molecules are classified as D form (Dextrorotatory
) and L (Laevorotatory) form depending
on whether they rotate the plane of plane –polarized light clock wise or
anticlockwise.
2. Naturally
occurring amino acids are L (Laevorotatory)
form
3. D-form aminoacids are rarely found in
bacterial cell walls and certain antibiotics (Gramicidin-S, Polymyxin,
Actinomycin-D and Valiomycin)
4.N-acetylmuramic acid (NAM) is a D-aminoacid containing tetrapeptide.
5. Peptide bond: covalent
bond formed between the α -amino group of one aminoacid and α -carboxylic group
of other forming a -CO-NH- linkage.
 |
| Peptide bond |
· Example of condensation reaction
· Exergonic
· Rigid
plannar
· Tripeptide means: 3 aminoacids +2 peptide
bond
6.
All aminoacids have high
melting point more than 2000C.
7.
Soluble in water
and alcohol, insoluble in non-polar solvents
8.
Aminoacids can exist as ampholytes/Zwitter ions
9.Essential Amino acids:
Arginine(Arg/R), Histidine(His/H), Isoleucine (Ile/I),
Leucine (Leu/L), Lysine (Lys/K), Methionine (Met/M), Phenylalanine (Phe/F),
Threonine
Memory tip:Any Help In Learning These Little Molecule
Proves Truly
Valuable.
This
stands for Arginine, Histidine, Isoleucine, Leucine, Threonine, Lysine,
Methionine, Phenylalanine, Tryptophan, Valine
10. Non Essential Amino acids:
Alanine(Ala/A),Asparagine(Asn/N),Aspartate(Asp/D),Cysteine(Cys/C),Glutamate(Glu/E),Glutamine(Gln/Q),Glycine(Gly/G),Proline(Pro/P),Serine(Ser/S),Tyrosine(Tyr/Y).
11. Histidine and Arginine
are essential amino acids for infants but not healthy adults
12. Cysteine and Tyrosine
are considered to be semi-essential amino acids. They are required by premature
infants and adults who are ill.
13. Simplest amino acid: Glycine
An aminoacid without asymmetrical carbon atom
An aminoacid without asymmetrical carbon atom
14. Acidic aminoacids: Glutamic acid and Aspartic acid
·
Glutamic acid -Most common aminoacid undergo
oxidative deamination
15. Basic aminoacids: Lysine and Arginine
·
Arginine contain guanidium group
·
Histones are rich in basic
aminoacids
16. Neutral
aminoacids: Glycine, Valine and Phenylalanine
17. Alcoholic
aminoacid: Serine and Threonine
18. Aromatic aminoacids: Tryptophan, Tryrosine,
Phenylalanine
· Aromatic aminoacids absorb
UV –light .This account for the characterization strong absorbance of
light by most proteins at wavelength of 280 nm
·Tryrosine forms skin pigment melanin
and two hormones Adrenaline and Thyroxine
19. Heterocyclic
aminoacids: Tryptophan and Histidine
· Tryptophan
(Bulkiest amino acid) has indole ring
· Tryptophan: precursor of IAA (Indole 3-acetic
acid- plant hormone) and nicotinamide (a
β vitamin )
· Amino acids with buffering
activity-Histidine
· Histidine
:only aminoacid having an ionisable side chain with a pka near neutrality (pk
value=6.1)
· Buffering capacity of plasma proteins and
haemoglobin is mainly due to Histidine residues
· Histidine
:more present in active site of an enzymes
· Histidine contain imidazole group
· Histidine found in intracellular and
extracellular fluids of most animals and plants.
20. Sulphur containing
aminoacid –Cysteine, Methionine
21. Aminoacids with amide
group: Asparagine, Glutamine
22. Proline (Secondary
imino amino acid) is rarely found within
alpha helix segments
23. Selenocysteine: 21st aminoacid
present in human protein.
24. Un common aminoacids:
· Collagen (A
fibrous protein of connective tissue): 4 hydroxyproline, 5-hydroxyglycine.
· Myosin (A
contractile protein of muscle):6-N Methyllysine
· Prothrombin (Blood
clotting protein):
25. Non-PROTEIN AMIINO ACIDS:
Ornithine and Citrulline are involved in the biosynthesis of Arginine and in the Urea cycle.
Ornithine and Citrulline are involved in the biosynthesis of Arginine and in the Urea cycle.
26. Glutathione is a
co enzyme of oxidation –reduction reactions which consist of glutamic acid,
glycine and cysteine. This chemical is important in preventing
oxidative damage to erythrocytes.
27. Aspartame(Nutrasweet) is artificial sweetner,
synthetic dipeptide, chemically it is -L-aspartyl-L-phenylalanine
28. Neurotransmitters
·
GABA (Gamma Amino Butryic Acid)-a derivative
of glutamic acid
·
Dopamine-derivative of tyrosine
29. Histamine- histidine derivative, allergic reaction mediator
30. Amino
acids as helix breakers-
Proline-Glycine-Tyrosine-Asparagine
31. Bend
producing amino acid :Glycine-Proline -serine -Threonine
32. Sickle cell haemoglobin differs from normal
haemoglobin by a single amino acid. In the β chain of sickle cell haemoglobin
,a valine (a hydrophobic acid) has replaced a glutamic acid( a negatively charged amino acid)
33. pI denotes isoelectric point/pH
pI=1/2(pk1+pk2)
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