Proteins are composed of chains of amino acids and perform essential functions in the body. There are 20 standard amino acids, some of which are essential and must be obtained through diet. Amino acids link together through peptide bonds to form polypeptide chains or proteins. Proteins have four levels of structure and take on complex shapes that enable their many functions like structure, movement, hormones, and enzymes. A deficiency or excess of proteins can cause health issues.

1. Proteins

2. Why We need to study About this?
Protein Engineering.
Structural Engineering.
Growth of body.
Major component of body
Curing Different Diseases.

3. What is Amino Acid?
• Amino acids are derivatives of carboxylic acids
formed by substitution of -hydrogen for amino
functional group
1 2

4. What is Protein?
The word protein came from a Greek word “Proteios”
Proteins are like long necklaces with differently
shaped beads. Each "bead" is a small molecule
called an amino acid.
Compounds composed of carbon, hydrogen, oxygen, and
nitrogen and arranged as strands of amino acids

5.  Structural
 Movement
 Transport
 Storage
 Hormone
 Protection
 Enzymes
Collagen; bones, tendons, cartilage
Keratin; hair, skin, wool, nails, feathers
Myosin & Actin; muscle contractions
Hemoglobin; transports O2
Lipoproteins; transports lipids
Casein; in milk. Albumin; in eggs
Insulin; regulates blood glucose
Growth hormone; regulates growth
Immunoglobulins; stimulate immunity
Snake venom; plant toxins;
Sucrase; catalyzes sucrose hydrolysis
Pepsin; catalyzes protein hydrolysis
Functions of Proteins

6. Protein Deficiency and Excess
• Protein-deficiency symptoms are always
observed when either protein or energy is
deficient
• Extreme food energy deficiency is marasmus
• Extreme protein deficiency is kwashiorkor
• The two diseases overlap most of the time
and together are called PEM

7. Protein Deficiency and Excess
• Protein-energy malnutrition (PEM)
– World’s most widespread malnutrition problem
– Includes both marasmus and kwashiorkor and
states of overlap
• Hunger
– Physiological craving for food
– Progressive discomfort, illness, and pain resulting
from the lack of food

8. What do Amino Acids Do?
 Amino acids are essential to life, have a role
in metabolism, and are important in
nutrition.
They form short polymer chains called peptides, as
well as longer chains that are called polypeptides or
proteins.
About 75 percent of the human body is made up of
chains of amino acids, which is why they are so vital
to how your system functions.
All the chemical reactions that occur in the body
depend on amino acids and the proteins they build.

10. Types of Amino Acids
Amino acids are classified as
• Nonpolar (hydrophobic)
with hydrocarbon side
chains.
• Polar (hydrophilic) with
polar or ionic side chains.
• Acidic (hydrophilic) with
acidic side chains.
• Basic (hydrophilic) with
–NH2 side chains.
Nonpolar Polar
Acidic Basic
3

11. Classification of amino acids based on structure:

19. C. Nutritional classification of amino
acids
• 1. Essential or indispensable amino acids :
• cannot be synthesized by the body supplied
through the diet
e.g., Arginine, Valine, Histidine, lsoleucine,
• Leucine, Lysine, Methionine, Phenylalanine,
• Threonine, Tryptophan.

20. • The two amino acids namely arginine and
histidine can be synthesized by adults and not
by growing children, hence these are
considered as semi-essential amino Acids.
• Thus, 8 amino acids are absolutely essential
hile 2 are semi-essential

21. • 2. Non-essential or dispensable amino acids :
The body can synthesize about '10 amino
acids to meet the biological needs, hence they
need not be consumed in the diet.
• These are-glycine, alanine, serine, cysteine,
aspartate,a sparagnie, glutamate, glutamine,
tyrosine and proline.

22. D. Amino acid classification based on
their metabolic fate :
• The carbon skeleton of amino acids can serve as a precursor for the
synthesis of glucose( glycogenico) r fat (ketogenico) r both.
• three groups:
• 1. Glycogenic amino acids : serve as precursors for the formation of
glucose or glycogen.
• e.g. alanine,aspartat
• Eg., lycine,methioninee tc.
• 2. Ketogenic amino acids : Fat can be synthesized from these amino acids.
Two amino acids leucine and lysine are exclusively ketogenic

23. • 3. Glycogenic and ketogenic amino acids :
• The four amino acids isoleucine, phenyl -
• alanine, tryptophan, tyrosine are precursors
for synthesis of glucose as well as fat.

24. Properties of Amino acids
• A. Physical properties:
• 1. Solubility :
• soluble in water ,
• Insoluble in organic solvents.
• 2. Melting points:
• melt at higher temperature so, often above
200˚C.

25. • 3. Taste:
• Sweet (Cly, Ala, Val),
• tasteless (Leu) or bitter (Arg, lle).
• Monosodium glutamate - flavoring agent in food industry,
and Chinese foods to increase taste and flavor.
• 4. Optical properties:
• except glycine, All the amino acid possesses optical isomers
due to the
• presence of asymmetric carbon atom.
• Some amino acids also have a second asymmetric carbon.
• e.g. isoleucine, threonine.

26. • 5. Amino acids as ampholytes :
• contain both acidic (-COOH) and basic
• (-NH2) groups.
• donate a proton or accept a proton, hence
amino acids are regarded as ampholytes.

27. Zwitterion or dipolar ion
• zwitter : derived from the German word which means hybrid.
• Zwitter ion (or dipolar ion) : a hybrid molecule containing positive
and negative ionic groups.
• Amino acids rarely : neutral form with free carboxylic (-COOH) and
free amino (-NH2) groups.
• In strongly acidic pH (low pH), the amino acid : positively charged.
• while in strongly alkaline pH (high pH), it is negatively charged
• Each amino acid has a characteristic pH (e.g. leucine, pH 6.0) at
• which it carries both positive and negative charges and exists as
zwitterion.

28. Isoelectric pH
• Isoelectric pH (pl) : pH at which a molecule
exists as a zwitterion or dipolar ion and carries
no net charge.
• molecule : electrically neutral
• For instance, leucine has two ionizable
• groups/ and its pl can be calculated as follows.

30. • Leucine - cation at pH below 6 and anion at pH
above 6.
• At the isoelectric pH (pl = 6.0), leucine is found
as zwitterion.
• pH of the medium determines the ionic nature
of amino acids.
• For the calculation of pl of amino acids with
more than two ionizable groups, the pKas for
all the groups have to be taken into account.

31. Titration of amino acids :
• At low pH, leucine : protonated form as cation.
• As the titration proceeds with NaOH, leucine loses its protons and
at isoelectric pH (pl), it becomes a zwitterion.
• Further titration results in the formation of anionic form of leucine.
• Some more details on isoelectric pH are
• discussed under the properties of proteins.

32. 4

33. Chemical properties of Amino Acids
• carboxyl (-COOH) group and amino (-NH2) group.
Reactions due to -COOH group:
• 1. Amino acids form salts (-COONa) with bases
and esters (-COOR') with alcohols.
2. Decarboxylation: produce corresponding Amines.
• This react ion assumes significance in the living
cells due to the formation of many biologically
important amines.

34. 3. Reaction with ammonia: The carboxyl group of dicarboxylic
amino acids reacts with NH3 to form amide.

35. Reactions due to -NH2 group
• 4. The amino groups behave as bases and
combine with acids (e.g. HCI) to form salts (-
NH3+Cl-).
5. Reaction with ninhydrin : The α-amino acids
react with ninhydrin to form a purple, blue or
pink colour complex (Ruhemann's purple)

36. Ninhydrin reaction is effectively used for the quantitative determination
of amino acids and proteins. (Note : Proline and hydroxyproline give
yellow colour with ninhydrin)
6.Colour reactions of amino acids : Amino acids can be identified by
specific colour reactions.
7.Transamination: Transfer of an amino group from an amino acid to a
keto acid to form a new amino acid is a very important reaction in amino
acid metabolism.
8.Oxidative deamination : The amino acids undergo oxidative
deamination to liberate free ammonia.

37. Formation of Peptide Bond
• When the amino group of an amino acid
combines with the carboxyl group of another
amino acid, a peptide bond is formed.

38. Formation of Peptide bond:

39. • rigid and planar with partial double bond in
character.
• lt generally exists in trans configuration.
• Both -C=O and –NH groups of peptide bonds
are polar and are involved in hydrogen bond
formation.

40. Nomenclature of peptides
Short peptides are often given a general name according to how many residues
(amino acids) are linked together.
Glycyl-alanyl-tyrosyl-glycine is a "TETRAPEPTIDE"
Alanyl-valyl-tryptophane is a "TRIPEPTIDE"
A general name for a long peptide is oligopeptide or POLYPEPTIDE.

41. The Structure of Proteins
• Side chain
– The unique chemical structure attached to the backbone
of each amino acid that differentiates one amino acid
from another
• Essential amino acids
– Amino acids that either cannot be synthesized at all by
the body or cannot be synthesized in amounts sufficient
to meet physiological needs

42. The Structure of Proteins
• Conditionally essential amino acid
– Amino acid that is normally nonessential, but must be
supplied by the diet in special circumstances when the
need for it exceeds the body’s ability to produce it
• Peptide bond
– Bond that connects one amino acid with another, forming
a link in a protein chain
• Amino acids link into long strands that coil and fold
to make a wide variety of different proteins

43. Essential AA
• Valin
• Leucin
• Isoleucine
• Threonine
• Lysin
• Methionin
• Phenylalanin
e
• Tryptophan
• Arginine
• Histidine
Nonessential AA
• Alanine
• Asparagine
• Aspartate
• Cysteine
• Glutamate
• Glutamine
• Glycine
• Proline
• Serine
• Tyrosine

44. Peptide Linkages
• Two dipeptides can result from reaction between A and S, depending on which COOH reacts
with which NH2 we get AS or SA
• The long, repetitive sequence of NCHCO atoms that make up a continuous chain is
called the protein’s backbone
• Peptides are always written with the N-terminal amino acid (the one with the free NH2
group) on the left and the C-terminal amino acid (the one with the free CO2H group) on
the right
• Alanylserine is abbreviated Ala-Ser (or A-S), and serylalanine is abbreviated Ser-Ala (or S-A)

45. Peptides and Proteins
• Proteins and peptides are amino acid polymers in which the
individual amino acid units, called residues, are linked together by
amide bonds, or peptide bonds
• An amino group from one residue forms an amide bond with the
carboxyl of a second residue
5

46. References:
Image 1: http://postimg.org/image/yq74xmbtz/
Image 2: http://postimg.org/image/yq74xmbtz/
Image 3: Biochemistry, U. Satyanarayan, Elsevier
India publication
Image 4: Biochemistry, U. Satyanarayan, Elsevier
India publication
Image 5: http://postimg.org/image/61ys84z1j/
Table : Biochemistry, U. Satyanarayan, Elsevier India
publication

47. THANK YOU
ANY QUERY
?