Proteins are large biomolecules composed of amino acid chains that fold into complex three-dimensional structures. They perform essential functions in the body such as structure, metabolism, transport, and defense. There are four levels of protein structure: primary, secondary, tertiary, and quaternary. The primary structure is the amino acid sequence. Secondary structures include alpha helices and beta sheets. Tertiary structure involves folding into a three-dimensional shape. Quaternary structure involves multiple polypeptide subunits. Proteins can be classified by function, conjugation with other groups, or derivation from other proteins. Denaturation involves unfolding the structure without breaking covalent bonds. Common denaturing agents are heat, pH changes

1. PROTEIN
S.U.VIKRAMAN
2017032052

2. Protein
• Large molecules composed of one or more chains
of amino acids in a specific order determined by the
base sequence of nucleotides in the DNA coding for the
protein.
• Proteins are required for the structure, function, and
regulation of the body's cells, tissues, and organs.
• Each protein has unique functions. Proteins are
essential components of muscles, skin, bones and the
body as a whole.
• Examples of proteins include whole classes of important
molecules, among them enzymes, hormones, and
antibodies.

3. Protein
• Amino Acid Sequence
• Protein Conformation
• Levels of Protein Structure
- Primary structure
-Secondary structure
-Tertiary structure
-Quaternary structure
• Classification of Proteins
• Function of proteins
• Denaturation of Protein

4. Peptides and Proteins
Peptides and proteins are polymers of twenty amino
acids connected to each other by peptide bonds.
Oligopeptide is formed of (2 –10) amino acids
-2 amino acids dipeptide,
-3 amino acids tripeptide,
-4 amino acids tetrapeptide ….etc.
Polypeptide is formed of more than 10 amino acids.
 In proteins, almost all carboxyl and amino groups are
combined in peptide linkage and not available for chemical
reaction (except for hydrogen bond formation).

5. FOOD PROTEIN
• Like peptides, proteins are formed from amino
acids through amide linkages.
• The structure of a protein is dependent on the
amino acid sequence (the primary structure) which
determines the molecular conformation (secondary
and tertiary structures).
• Proteins sometimes occur as molecular aggregates
which are arranged in an orderly geometric fashion
(quaternary structure).
• The sequences and conformations of a large
number of proteins have been elucidated and
recorded in several data bases.

6. Levels of Protein Structure
1)PRIMARY STRUCTURE
• It is the amino acid sequence of the polypeptide chain
linked by peptide bonds.
• It is characteristic for every protein.
• All proteins have an
• N-terminal end (with a free amino group) and
• C-terminal end (with a free carboxyl group).
• Polypeptide chain sequence is written according to the
sequence of amino acid residues from the N to C
terminus amino acids.
• Primary structure

7. 2.SECONDARY STRUCTURE
• Is the local spatial arrangement of the polypeptide’s
backbone (peptide bond) atoms without regard to the
conformations of its side chains.
• Peptide bonds contain polar amide hydrogen atoms (with
a partial positive charge) and polar carbonyl oxygen
atoms (with a partial negative charge).
• This allows hydrogen bonds to form between peptide
bonds in different parts of the chain.
• The polypeptide chain can take different shapes or
patterns in different parts of the chain, and these
patterns are called the secondary protein structure.
• There are 2 types of secondary structure:
-Alpha helix (α-helix)
• -Beta-pleated sheet (β-pleated sheet).

8. Alpha helix
•A spiral, compact, rod like structure
•Mostly right handed α-helix, with R groups protruding outside
•Stabilized by numerous hydrogen bonds which are formed
between carbonyl oxygen (C=O, hydrogen acceptor) and
peptide nitrogen (NH, hydrogen donor).
•Forms about 100% of fibrous protein
-keratin
-80% of the globular protein; hemoglobin.
Secondary structure

9. Beta helix
•Almost fully extended and its surface appear
pleated.
•Found in fibrous and globular protein.
•Formed of 1 or more polypeptide chains.
•Stabilized by hydrogen bonds between
peptide bonds

10. 3.TERITIARY STRUCTURE
GLOBULAR
PROTEIN
FIBROUS
PROTEIN
•Is the three dimensional structure of a single polypeptide chain giving prot
its characteristic shape.
I- Globular proteins (enzymes)
•Approximately spherical shape- water Soluble.
II- Fibrous proteins (structural proteins)
•Rod-like shape
•Poor water solubility.
•Cross links and bonds in 3ry structure:
•S-S bond, Ionic, Hydrophobic interactions
and H-bonding.

11. Forces that stabilize tertiary
structure
• These are bonds that form between side chains of amino
acids of the same polypeptide chain:
• 1.Disulfide bonds.
• 2.Hydrophobic interactions.
• 3.Hydrogen bonds.
• 4.Ionic interactions.
• 5.Van der Waal’s forces

12. 4.QUATERNARY STRUCTURE
•Many proteins are composed of two or more polypeptide
chains which are loosely associated through noncovalent
interactions (hydrogen bonds, ionic bonds and
hydrophobic interactions).
•An individual polypeptide is termed subunit or monomer.
•According to the number of subunits, proteins are either:
-dimeric (2 subunits),
-trimeric (3 subunits),
-tetrameric (4 subunits; e.g. HB)
-oligomeric (many subunits).

13. CLASSIFICATION
OF PROTEIN
SIMPLE PROTEIN
COMPOUND
PROTEIN
DERIVED
PROTEIN
1.Albumin
2.Globulins
3.Histones
1.Phosphoproteins
2.Glycoproteins
3.Chromoproteins
4.Lipoproteins
5.Nucleoproteins
6.Metalloproteins
Results from
denaturation or
cleavage of
native proteins
by the action of
acids, alkali or
enzymes.

14. Conjugated protein
• Proteins can be modified to include other chemical
groups “prosthetic groups” besides amino acids:
Class Prosthetic group example
•Lipoproteins •Lipids •VLDL
•Glycoproteins •Carbohydrates •Immunoglobulin
G
•Phosphoproteins •Phosphate
groups
•Casinogen of
milk
•hemoproteins •Heme (iron
porphyrin )
•Hemoglobin

15. Protein Function
• Catalysis – enzymes
• Structural – keratin
• Transport – hemoglobin
• Toxins – rattle snake venom, ricin
• Contractile function – actin, myosin
• Hormones – insulin
• Storage Proteins – seeds and eggs
• Defensive proteins – antibodies

16. Denaturation of Protein
• The term denaturation denotes a reversible or irreversible
change of native conformation (tertiary structure) without
cleavage of covalent bonds (except for disulfide bridges).
• The primary structure of the protein is not changed because the
peptide bonds are not affected
• Denaturing agents include:
1.Heat
2.Changes in pH (concentrated acids or alkali)
3.Ultraviolet rays
4.X ray
5.High salt concentration
6.Heavy metals.

17. Denaturation
• Denaturation is possible with any treatment that cleaves
hydrogen bridges, ionic or hydrophobic bonds.This can be
accomplished by: changing the temperature, adjusting the
pH, increasing the interface area, or adding organic
solvents, salts, urea, or detergents such as sodium
dodecyl sulfate.
• Denaturation is generally reversible when the peptide
chain is stabilized in its unfolded state by the denaturing
agent and native conformation can be re-established after
removal of the agent.
• Irreversible denaturation occurs when the unfolded
peptide chain is stabilized by interaction with other chains
(as occurs for instance with egg proteins during boiling).
During unfolding reactive groups, such as thiol groups,
that were blocked, may be exposed.Their participation in
the formation of disulfide bonds may also cause an
irreversible denaturation.

18. Applications of protein
denaturing
• 1- Boiling eggs: Change in albumin shape and solubility.
• 2- Cooking meat: Easily chewable, digestible.
• 3- Swabbing skin with alcohol (disinfectant):
Denatures/kills bacteria and viruses.
• 4- HCl in our stomach: denatures proteins and making it
easily digestible by enzymes
• So, eating cooked eggs, meat and liver is more useful to
humans than eating them raw

19. THANK YOU
S.U.VIKRAMAN