Protein

1. Biochemistry
Presentation

2. Topic
Protein
Primary Structure
Secondary Structure
Tertiary structure
Quaternary structure
Biological significance

3. Protein:
 Proteins are the most abundant organic molecules of the living system.
 They constitute about 50% of the cellular dry weight.
 They constitute the fundamental basis of structure and function of life.

4.  In 1839, Dutch chemist G.J. Mulderwas first
to describe about proteins.
 The term protein is derived from a Greek
word proteios,meaning first place.
 The proteins are nitrogenous
macromolecules that are composed of many
aminoacids.

5. Amino Acids
 Amino acids are a group of organic compounds
containing two functional groups –amino and
carboxyl.
 The amino group[ -NH2] is basic while the
carboxyl group [COOH] is acidic in nature.
 There are about 300 aminocids occur in nature.
Only 20 of them occur in proteins.

6. Structure of Amino Acid
Each amino acid has 4 different
groups attatchedto αcarbon ( which
is C atom next to COOH).These 4
groups are : amino group, COOH
group , Hydrogen atom and side
chain(R).

7. Peptide bond formation
 α-carboxyl group of one amino acid (with side chain R1)
forms a covalent peptide bond with α-amino group of
another amino acid (with side chain R2) by removal of a
molecule of water.
 The result is : Dipeptide.

8.  The dipeptidecan then form a second peptide bond
with a third amino acid( with side chain R3) to give
tripeptide.
 Repetition of this process generates a polypeptide or
protein of specific aminoacidsequence.
 Has 40% double bond character, caused by
resonance.

9. Structures of protein
 Proteins have different levels of organisation
 Primary Structure
 Secondary Structure
 Tertiary Structure
 Quaternary Structure

11. Primary Structure
 The primary structure of protein refers to the sequence of amino acids
present in the polypeptide chain.
 Amino acids are covalently linked by peptide bonds or covalent bonds.
 Each component amino acid in a polypeptide is called a " residue” or
“moiety”.
 By convention the primary structure of protein starts from the amino terminal
(N) end and ends in the carboxyl terminal (C) end.

12. Secondary Structure
 It is a local, regularly occurring structure in proteins and is mainly formed
through hydrogen bonds between backbone atoms.
 Pauling & Corey studied the secondary structures and proposed 2
conformations
 o αhelix
 o βsheets.

13. Tertiary structure
 The tertiary structure defines the specific overall 3-D shape of the
protein.
 Tertiary structure is based on various types of interactions between
the side-chains of the peptide chain.

14. Tertiary structure stabilization
 In globular proteins
 Tertiary interactions are frequently stabilized by
sequestration of hydrophobic amino acid residues in the
protein core.
 Consequent enrichment of charged or hydrophilic residues
on the protein's water-exposed surface.
 In secreted proteins
 Di-sulfide bonds between cysteine residue helps to
maintain the protein's tertiary structure

15. Interactions in tertiary structure
 1. Disulfide bonds
 2. Hydrophobic interactions
 3. Hydrogen bonds
 4. Ionic interactions
 5. Vander Waals force

16. Quaternary structure

17.  The quaternary protein structure involves the clustering of several
individual peptide or protein chains into a final specific shape.
 A variety of bonding interactions including hydrogen bonding, salt
bridges, and disulfide bonds hold the various chains into a particular
geometry.
 Two kinds of quaternary structures: both are multi subunit proteins.
Homodimer :
 association between identical polypeptide chains.
 Heterodimer:
 interactions between subunits of very different structures.
 The interactions within multi subunits are the same as that found in
tertiary and secondary structures

18. Biological Significance of Proteins