For science & medical students

1. AMINO ACIDS
&
PROTEINS:
By
Dr. P. R. Padole
Department of Chemistry
Shri Shivaji Science 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 (-NH2).
R CH COOH
NH2
-Carbon
Amino acid
R CH C OH
NH2
-Carbon
Amino acid
O
Where, R may be H, alkyl group, or may be quite complex containing other functional groups.
H CH COOH
NH2
For examples:
1)
Glycine
CH3 CH COOH
NH2
2)
Alanine
(Amino acetic acid) ( -Amino propionic acid)

8. Amino acid containing
more number of
carboxyl group (-COOH)
as compared to
amino group
(-NH2) are called as
acidic amino acids.
Amino acid containing
same number of
carboxyl group (-COOH)
and amino group (-NH2)
are called as
neutral amino acids.
Amino acid containing
more number of
amino group (-NH2)
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
NH2
Glycine
(Amino acetic acid)
NH2
Aspartic acid
CH2 CH COOHHOOC
Lysine
NH2
NH2-CH2-CH2-CH2-CH2-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:
Or Preparation of Glycine:
 When potassium phthalimide is treated with ethyl
chloro-acetate; to form substituted phthalimide, which on acid
hydrolysis; to form phthalic acid and Glycine as an amino acid.
Q.1) Explain Gabriel phthalimide synthesis. (S-16, 4 Mark)
Q.2) Write short account on Gabriel phthalimide synthesis. (W-17, 4 Mark)
C
N K
C
O
O
Cl CH2COO-C2H5
C
C
O
O
OH
OH
H2N-CH2-COOH
C
N CH2COO C2H5
C
O
O
+
Ethyl chloro acetate
Potassium Phthalimide
+
Phthalic Acid
Glycine
- KCl
H2O / H
Acid hydrolysis
HO---H
H
O
---H
H---OH
Intermediate product
+ C2H5OH

11. Strecker Synthesis:
Or Preparation 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 NH3; to form α-amino nitrile.
Q.1) How will you convert Acetaldehyde to Alanine by Strecker synthesis? (S-12, 2 Mark)
Q.2) Give Strecker’s synthesis of Amino Acid. (S-16, 4 Mark)
Q.3) How alanine is prepared by Strecker’s synthesis? (W-16, 2 Mark)
Q.4) Write short notes on: Strecker’s synthesis for amino acids. (W-17, 2 Mark)
Q.5) Strecker Synthesis is used for synthesis of
a) Nitobenzene, b) Diazonium Salt c) α amino acid d) Polypeptide
NH4Cl KCN NH3 HCN KCl+ + +
CH3 C O
+ NH3CH3 C
H
OH CH3 C
H
CN
NH2
+
H
CN
H CN
Acetaldehyde
Hydrogen cyanide
Cyanohydrin
- H2O
H---NH2
-Amino nitrile

12. Strecker Synthesis:
Or Preparation of Alanine from Acetaldehyde:
 Step-2)
When α-amino nitrile is hydrolysed (acid
hydrolysis); to form Alanine as an amino acid.
H2O / H
Alanine
CH3 C
H
C N
NH2
-Amino nitrile
Acid hydrolysis
CH3 C
H
COOH
NH2
HO---H
O---H2
+ NH3

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Or Dipolar ion:
Or Dipolar 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:
Or Dipolar ion:
 In aqueous solution, amino acids exist as charged molecules.
 This is because; they contain both an acidic –COOH group
and basic –NH2 group in the same molecule.
 Transfer of a proton takes place in a kind of internal acid-
base reaction.
R CH C O H
NH2
O
..
R CH C O
NH3
O
Zwitter ion
or Dipolar ion
The product of this reaction is called a zwitterion
(or dipolar ion).
A zwitterion is an amino acid molecule containing both a positive and
a negative charge.
transferring a proton internally
The zwitterion is the more common form in which amino
acids exist in aqueous solution.

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Define Zwitterion.
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+
-
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 zwitterion form are polar (amphoteric).
 That is, they react readily with acids or bases.
 (i) Amino acid in Acidic solution:
 The reaction with acids converts the carboxylate group (-COO-) into
carboxyl group (-COOH).
 In acidic solutions, amino acids exist as positive ions
and are attracted toward the cathode (negative electrode).
R CH C O
NH3
O
Zwitter ion
or Dipolar ion
+ H
(from acid)
R CH C OH
NH3
O
(positive ion)

18. L o g o
Isoelectric point:
 (ii) Amino acid in Basic solution:
The reaction with bases converts the ammonium
group (-NH3
+) into amino group (-NH2).
 In basic solutions, amino acids exist as
negative ions and are attracted toward the
anode (positive electrode).
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R CH C O
NH2 H
O
Zwitter ion
or Dipolar ion
+ OH R CH C O
NH2
O
(negative ion)
+ H2O

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 isoelectric point.
 Defination:
 1) The isoelectric point is 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 pH is called
isoelectric point.
 OR 3) The pH at which an amino acid exists as dipolar ion
in solution is called Isoelectric point.
 OR 4) The pH at which an amino acid in the solution has
zero charge is Isoelectric point.
19

20. 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 isoelectric point.
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at the isoelctric pH
At high pH
(base)
At Low pH
Acid
cathodeanode
R CH C O
NH3
O
Zwitter ion
or Dipolar ion
R CH C OH
NH3
O
(positive ion)
R CH C O
NH2
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:
 When two or more amino acids bonded
together by a peptide linkage (-CONH-, also
called as amide linkage) formed with the
elimination of water is 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)
NH2 C C OH + NH C COOH
CH3
AlanineGlycine Glycylalanine (Dipeptide)
H
H
O
H
H
NH2 C C NH C COOH
CH3H
H
O
H
Peptide linkage
- H2O

24. Amino
Acid 1
NH2
R
COOH
C
H
Amino acids have an amino group,
carboxyl group, R group and hydrogen.

25. H2O
Amino
Acid 2
N
R
COOH
C
H
H
H
Amino
Acid 1
NH2
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
H2
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
(–NH2) 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:
NH2 C C OH + NH C COOH
CH3
AlanineGlycine Glycylalanine (Dipeptide)
H
H
O
H
H
NH2 C C NH C COOH
CH3H
H
O
H
Peptide linkage
- H2O
NH2 C COOH
CH3
+ NH2 C COOH NH2 C C NH C COOH
HO
CH3
GlycineAlanine Alanylglycine (a dipeptide)
- H2O
H
H
H H H
NH2 C C NH C COOH
CH3O
H-NH C COOH+ NH2 C C NH C C
CH3
O
NH C COOH
O
Glycylalanine (a dipeptide) Glycine Glycylalanylglycine
(a tripeptide)
- H2O
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. DefenseEnzyme
Support
Transport
Motion
Regulation
Proteins can be functionally classified.
Hemoglobin
AntibodyProtease
Keratin
Actin
Insulin
Carries O2
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 polypeptide molecules that
contain many peptide subunits.

34. Proteins (Polypeptides):
 Proteins are polymers of α-amino acids bonded
by peptide linkages.
 Proteins are polypeptides.

H N C C OH
Amino acid
OH
H
R
H N C C OH
Amino acid
OH
H
R'
H N C C OH
Amino acid
OH
H
R''
+ + + ----
- n H2O
N C C
OH
H
R
N C C
OH
H
R'
N C C
OH
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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