Amino acids & proteins by dr. pramod r. padole

For science & medical students

1. AMINO ACIDS
&
PROTEINS:
By
Dr. P. R. Padole
Department of Chemistry
ShriShivajiScience College, Amravati.

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Amino acids and Proteins:

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7. Amino acids :
Defination:
Amino acids are compounds that contain at
least one carboxyl group (-COOH) and
one amino group (-NH
2). R CH COOH
NH
2
-Carbon
Amino acid
R CH C OH
NH
2
-Carbon
Amino acid
O
Where, R may be H, alkyl group, or may be quite complex containing other functional groups.
H CH COOH
NH
2
For examples:
1)
Glycine
CH
3 CH COOH
NH
2
2)
Alanine
(Amino acetic acid) ( -Amino propionic acid)

8. Amino acid containing
more number of
carboxyl group (-COOH)
as compared to
amino group
(-NH
2) are called as
acidic amino acids.
Amino acid containing
same number of
carboxyl group (-COOH)
and amino group (-NH
2)
are called as
neutral amino acids.
Amino acid containing
more number of
amino group (-NH
2)
as compared to
carboxyl group
(-COOH) are called as
basic amino acids.
Classification of Amino Acids:
Neutral
Amino Acids:
Q.1) Discuss / Give the classification of amino acids with suitable examples. (W-13 & S-14, 2-3 Mark)
Acidic
Amino Acids:
Basic
Amino Acids:H CH COOH
NH
2
Glycine
(Amino acetic acid) NH
2
Aspartic acid
CH
2 CH COOHHOOC Lysine
NH
2
NH
2-CH
2-CH
2-CH
2-CH
2-CH-COOH

9. Preparation of Amino Acids:
Gabriel
Phthalimide
Synthesis:
Or
Preparation of Glycine:
Amino Acids
Preparation
Strecker
Synthesis:
Or
Preparation of Alanine:

10. Gabriel Phthalimide Synthesis:
OrPreparation of Glycine:
 When potassium phthalimideis treated with ethyl
chloro-acetate; to form substituted phthalimide, which on acid
hydrolysis; to form phthalicacid and Glycineas an amino acid.
Q.1) Explain Gabriel phthalimidesynthesis. (S-16, 4 Mark)
Q.2) Write short account on Gabriel phthalimidesynthesis. (W-17, 4 Mark)C
N K
C
O
O
Cl CH
2COO-C
2H
5
C
C
O
O
OH
OH
H
2N-CH
2-COOH
C
N CH
2COO C
2H
5
C
O
O
+
Ethyl chloro acetate
Potassium Phthalimide
+
Phthalic Acid
Glycine
- KCl
H
2O / H
Acid hydrolysis
H
O
-
-
-
H
H
O
- - - H
H---OH
Intermediate product
+ C
2H
5OH

11. Strecker Synthesis:
OrPreparation of Alanine from Acetaldehyde:
Step-1)
When acetaldehyde is treated with HCN(prepared from
mixture of ammonium chloride and potassium cyanide); to form
cyanohydrin, which is reacted with NH
3; to form α-amino nitrile.
Q.1) How will you convert Acetaldehyde to Alanineby Streckersynthesis?(S-12, 2 Mark)
Q.2) Give Strecker’ssynthesis of Amino Acid. (S-16, 4 Mark)
Q.3) How alanineis prepared by Strecker’ssynthesis? (W-16, 2 Mark)
Q.4) Write short notes on: Strecker’ssynthesis for amino acids. (W-17, 2 Mark)
Q.5) StreckerSynthesis is used for synthesis of
a) Nitobenzene, b) DiazoniumSalt c) α amino acidd) PolypeptideNH
4Cl KCN
NH
3HCN KCl
+ + + CH
3CO
+ NH
3CH
3C
H
OH CH
3C
H
CN
NH
2
+
H
CN
H CN
Acetaldehyde
Hydrogen cyanide
Cyanohydrin
- H
2O
H---NH
2
-Amino nitrile

12. Strecker Synthesis:
OrPreparation of Alanine from Acetaldehyde:
Step-2)
When α-amino nitrileis hydrolysed(acid
hydrolysis); to form Alanineas an amino acid.H
2O

/ H
Alanine
CH
3C
H
C N
NH
2
-Amino nitrile
Acid hydrolysis
CH
3C
H
COOH
NH
2
HO---H
O---H
2
+ NH
3

13. Company
LOGO Zwitterions:
OrDipolar ion:
OrDipolar Nature of Amino Acids:
Q.1) Explain the term: Zwitterion. (S-12,S-14, W-14, S-15 & W-15, 2 Mark)
Q.2) Define Zwitterion. (W-16, 2 Mark)
Q.3) Write short account on Zwitterion. (S-17, 2 Mark)

14. Zwitterions:
OrDipolar ion:
In aqueous solution, amino acidsexist as charged molecules.
This is because; they contain both an acidic –COOH group
and basic –NH
2group in the same molecule.
Transfer of a protontakes place in a kind of internal acid-
base reaction.R CH C O H
NH
2
O
..
R CH C O
NH
3
O
Zwitter ion
or Dipolar ion
The product of this reaction is called a zwitterion
(or dipolar ion).
A zwitterionis an amino acid molecule containing both a positive and
a negative charge.
transferring a proton internally
The zwitterionis the more common form in which amino
acids exist in aqueous solution.

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Define Zwitterion.
15
+
-
Zwitterions contain both a positive and a negative charge.
They are neutral and have no net charge

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Isoelectric point:
Q.1) Explain the term: Isoelectric point. (S-12, S-13, W-13, S-14, W-14, S-15 & W-15, 1-2 Mark)
Q.2) At a certain pH of the solution, the amino acid molecule would not migrate to any electrode; this pH
is called:
(a) Neutral point (b) Isoelectric point(c) Cations (d) Anions (S-14, ½ Mark)
Q.3) The pH at which an amino acid exists as dipolar ion in solution is called Isoelectric point. (W-15, ½ Mark)
Q.4) What is isoelectric point? (S-17, 1Mark)
Q.5) The pH at which an amino acid in the solution has zero charge is Isoelectric point. (W-17, ½ Mark)
Q.6) Write short notes on: Isoelectric point. (W-17, 2 Mark)

17. L o g o
Isoelectric point:
Amino acids in the zwitterionformare polar (amphoteric).
That is, they react readily with acids or bases.
(i) Amino acid in Acidic solution:
The reaction with acids converts the carboxylategroup (-COO
-
) into
carboxyl group (-COOH).
 In acidic solutions, amino acids exist as positiveions
and are attracted toward the cathode (negative electrode).R CH C O
NH
3
O
Zwitter ion
or Dipolar ion
+H
(from acid)
R CH C OH
NH
3
O
(positive ion)

18. L o g o
Isoelectric point:
(ii) Amino acid in Basic solution:
The reaction with bases converts the ammonium
group (-NH
3
+
) into amino group (-NH
2).
In basic solutions, amino acids exist as
negative ions and are attracted toward the
anode (positive electrode).
18R CH C O
NH
2 H
O
Zwitter ion
or Dipolar ion
+OH
R CH C O
NH
2
O
(negative ion)
+ H
2O

19. L o g o
Isoelectric point:
At a certain pH (that is, at certain hydrogen ion concentration)
amino acids would not migrate to any electrode and exist as
neutral zwitterions.
This pH is called isoelectricpoint.
Defination:
1) The isoelectricpointis the pH at which an amino acid
exists completely as the zwitterions.
OR 2) At a certain pH of the solution, the amino acid
molecule would not migrate to any electrode; this pHis called
isoelectricpoint.
OR3) The pH at which an amino acid exists as dipolar ion
in solution is called Isoelectricpoint.
OR4) The pH at which an amino acid in the solution has
zero charge is Isoelectricpoint.
19

20. L o g o
Isoelectric point:
At a certain pH (that is, at certain hydrogen ion concentration) amino acids would not
migrateto any electrode and exist as neutral zwitterions.
This pH is called isoelectricpoint.
20at the isoelctric pH
At high pH
(base)
At Low pH
Acid
cathodeanode
R CH C O
NH
3
O
Zwitter ion
or Dipolar ion
R CH C OH
NH
3
O
(positive ion)
R CH C O
NH
2
O
(negative ion)
(Negative electrode)(Positive electrode)

21. Nonionic and zwitterion forms of amino acids
The zwitterion predominates at neutral pH
Week acid
Week base
Zwitterion = in German for “hybrid ion”

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PEPTIDES or Dipeptide:
Q.1) Explain the term: Dipeptide. (S-13, 2 Mark)
Q.2) What are peptides? Give the classification of peptides.(W-14, 2 Mark)
Q.3) Write short account on Peptides. (S-17, 2 Mark)
Q.4) In peptide, linkage between amino and carboxylic group is peptide linkage.

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PEPTIDES or Dipeptide:
 Whentwoor moreamino acids bonded
together by a peptide linkage(-CONH-, also
called asamide linkage) formed with the
elimination of wateris called as peptides.
Classification of Peptides
Dipeptide Tripeptide Tetrapeptide Polypeptide
(Two amino acids
combine)
(Three amino acids
combine)
(Four amino acids
combine)
(Many amino acids
combine) NH
2CC OH+ NHCCOOH
CH
3
AlanineGlycine
Glycylalanine (Dipeptide)
H
H
O
H
H
NH
2CCNHCCOOH
CH
3H
H
O
H
Peptide linkage
- H
2O

24. Amino
Acid 1
NH
2
R
COOH
C
H
Amino acids have an amino group,
carboxyl group, R group and hydrogen.

25. H
2O
Amino
Acid 2
N
R
COOH
C
H
H
H
Amino
Acid 1
NH
2
R
C
C
H
O
O
H
Peptide bonds form by
dehydration synthesis

26. Amino
Acid 2
R
COO
H
C
H
Amino
Acid 1
N
H
2
R
C
H

27. Classification of Peptides:
Tripeptide:
When
three
amino acids
combine
together by a
peptide linkage
and the
product
formed is
called a
tripeptide.
Dipeptide:
When
two
amino acids
combine together
by a peptide
linkage between
the amino group
(–NH
2) of one
amino acid and the
carboxyl group (-
COOH) of another
amino acid and the
product formed is
called a Dipeptide.
Two Three Four Many
Polypeptide:
When
many
amino acids
combine
together by a
peptide linkage
and the
product is
called a
polypeptide.
Proteins are
polypeptides
containing at
least 100 or more
amino acids.
Tetrapeptide:
When
four
amino acids
combine
together by a
peptide linkage
and the product
is called a
tetrapeptide.

28. Examples:NH
2CC OH+ NHCCOOH
CH
3
AlanineGlycine
Glycylalanine (Dipeptide)
H
H
O
H
H
NH
2CCNHCCOOH
CH
3H
H
O
H
Peptide linkage
- H
2O NH
2CCOOH
CH
3
+NH
2CCOOH NH
2C CNHCCOOH
HO
CH
3
Glycine
Alanine
Alanylglycine (a dipeptide)
- H
2O
H
H
H H H NH
2CCNHCCOOH
CH
3O
H-NHCCOOH+ NH
2CCNHCC
CH
3
O
NHCCOOH
O
Glycylalanine (a dipeptide) Glycine
Glycylalanylglycine
(a tripeptide)
- H
2O
H
H
H
H
H
H
H H H
H

29. What are PROTEINS?
Proteins are large, complex molecules that serve
diverse functional and structural roles within cells.
OR
Proteins are polymers of α-amino acids bonded by
peptide linkages.
Proteins are polypeptides

30. Proteins are the ACTION FORCE
in the cell.

31. Defense
Enzyme
Support
Transport
Motion
Regulation
Proteins can be functionally classified.
Hemoglobin
Antibody
Protease
Keratin
Actin
Insulin
CarriesO
2
Fights Viruses
Degrades
Protein
Forms Hair
and
Nails
Contracts Muscle Fibers
Controls
Blood Glucose

33. Proteins are chains of amino acids.
C
O
O
H
N
H
H
N
H
H
Short chains of amino acids are called
peptides.
Proteins are polypeptidemolecules that
contain many peptide subunits.

34. Proteins (Polypeptides):
Proteins are polymers of α-amino acidsbonded
by peptide linkages.
Proteins are polypeptides.
 H N C C OH
Amino acid
O
H
H
R
H N C C OH
Amino acid
O
H
H
R'
H N C C OH
Amino acid
O
H
H
R''
+ + + ----
- n H
2O
N C C
O
H
H
R
N C C
OH
H
R'
N C C
O
H
H
R''
Protein segment
Peptide linkages
They occur in all living cells.
Proteins are present in muscle, skin, hair, and other tissue that make up the
body’s non-bony structure.
Without proteins life would not be possible.

35. References
References….
•Organic Chemistry, F. A. Carey
•Organic Chemistry, T. W. Solomons
•Organic Chemistry, I. L. Finar
•Advance Organic Chemistry, J. D. March
•A Textbook of Organic Chemistry, Arun Bahl & B. S. Bahl

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