2. What are proteins?
What are proteins made of ?
Classification of amino acids: selected properties.
Peptide bonds.
Protein Structures.
Classification of Structures.
Primary Structure.
Secondary Structure.
Tertiary Structure.
Quaternary Structure.
Index
3. Proteins are large biological molecules,
or macromolecules, consisting of one or
more long chains of amino acid residues.
Proteins perform a vast array of functions
within living organisms ∼
Catalysing metabolic reactions
Replicating DNA
Responding to stimuli
Transporting molecules from one
location to another.
What are proteins?
4. Proteins are made up of smaller building
blocks called amino acids, joined together
in chains.
Some proteins are just a few amino acids
long, while others are made up of several
thousands.
These chains of amino acids fold up in
complex ways, giving each protein a
unique 3D shape.
There are 20 different amino acids.
What are proteins made of ?
6. The amide group is planar with N-H
trans to C=O (trans-peptide bond).
C-N of the peptide bond has partial
double bond -character.
Peptide bonds
7. Protein structure is the bio molecular structure
of a protein molecule.
Proteins are polymers – specifically
polypeptides -sequences formed from various L-
α-amino acids. Each unit of a protein is called an
amino acid residue because it is the residue of
every amino acid that forms the protein by
losing a water molecule.
proteins fold into one or more specific spatial
conformations, driven by a number of non-
covalent interactions such as hydrogen bonding,
ionic interactions, Van der Waals forces, and
hydrophobic packing.
Protein structures
8. Depending on the complexity of
the structure, it can be classified
as –
1) Primary structure
2) secondary structure
3) tertiary structure
4) quaternary structure
Classification of Structures
9. The primary structure of a peptide or protein
is the linear sequence of its amino acid
structural units, and partly comprises its
overall bimolecular structure. By convention,
the primary structure of a protein is reported
starting from the amino-terminal (N) end to
the carboxyl-terminal (C) end.
The amino acids differ in structure by the
substituent on their side chains. These side
chains confer different chemical, physical and
structural properties to the final peptide or
protein.
Each amino acid has both a one-letter and
three-letter abbreviation. These abbreviations
are commonly used to simplify the written
sequence of a peptide or protein.
Primary Structure
10. The term secondary structure refers to
the interaction of the hydrogen bond
donor and acceptor residues of the
repeating peptide unit.
The two most important secondary
structures of proteins, the alpha helix
and the beta sheet, were predicted by
the American chemist Linus Pauling in
the early 1950s.
Both the alpha helix and the beta sheet
represent a way of saturating all the
hydrogen bond donors and acceptors in
the peptide backbone.
Secondary structures
11. The tertiary structure of a protein is a
description of the way the whole chain
(including the secondary structures) folds
itself into its final 3-dimensional shape.
Shape is stabilized by various interactions,
among the R groups of polypeptide chain.
Tertiary structure
12. The quaternary protein
structure involves the clustering
of several individual peptide or
protein chains into a final
specific shape.
There are two major categories
of proteins with quaternary
structure - fibrous and globular.
Quaternary Structures