This document discusses the structure and classifications of proteins. It describes the primary, secondary, tertiary, and quaternary structures of proteins. The primary structure is the linear sequence of amino acids. Secondary structures include alpha-helices and beta-sheets formed by hydrogen bonding between amino acids. Tertiary structure refers to the 3D conformation of the entire polypeptide chain. Quaternary structure involves interactions between multiple polypeptide subunits. The document also classifies proteins based on their function, composition/solubility, and nutritional levels. Common protein structures and several color reaction tests for identifying proteins are outlined.

1. Structure and Classifications of Proteins
Prepared By:-
Harsh Jaswal
(CUHP19CCS09)
M.Sc Chemistry (3rd Semester)

2. .
Can any
body tell me
what are
Proteins?
Proteins are polymers
of L-alpha Amino Acids.
The term protein is
derived from a Greek
word proteios, meaning
holding the first place.

3. .
Can we
see
Proteins?
No, we can’t see Proteins
from our naked eyes.
However we can see
them via Microscope, and
thus we have different
types of Structures of
Proteins.

4. ,m
Can we
discuss
different
structures of
Proteins?
Yes, we should
discuss the
different
Structures of
Proteins.

5. PRIMARY STRUCTURE OF
PROTEIN
The linear sequence of
amino acids forming the
backbone of proteins
(polypeptides).What are
polypeptid
es?

6. r r
Two AA
covalently joined
through a
substituted amide
linkage – peptide
bond. When
many AA joined
together they are
called Polypeptide
bond.

7. SECONDARY STRUCTURE OF
PROTEINSThe spatial arrangement of
protein by twisting of the
polypeptide chain.
The conformation of
polypeptide chain by
twisting or folding is referred
to as secondary structure.
The amino acids are
located close to each other
in their sequence.
Two types of secondary
structures, alpha-helix and
beta-sheet, are mainly
identified.

8. Alpha(α) Helix
α helix is twisted by an
equal amount about each α
carbon.
Stability of an α helix
arises primarily from
hydrogen bonds.
Supplemented by van der
Waals interactions.
All the peptide bonds,
except the first and last in a
polypeptide chain,
participate in hydrogen
bonding.
Each turn of α -helix
contains 3.5 amino acids
and travels a distance of
0.54 nm. The spacing of
each amino acid is 0.15
nm. α -Helix is a stable

9. Beta (β)-Pleated sheet
This is the second type
of structure by Pauling
and Corey.
β -Pleated sheets (or
simply β -sheets) are
composed of two or more
segments of fully
extended peptide chains.
ln the β -sheets, the
hydrogen bonds are
formed between the
neighboring segments of
polypeptide chain(s).

10. Tertiary Structure
Entire 3-dimensional
conformation of a
polypeptide.
 Beside H bond, sulfide
bond (-S-S), ionic
interaction and
hydrophobic bond.
Domains: The term
domain is used to
represent the basic units
of protein structure
(tertiary) and function. A
polypeptide with 200
amino acids normally
consists of two or more
domains

11. Quaternary Structures
A great majority of the
proteins are composed of
single polypeptide chains.
Some of the proteins,
however, consist of two or
more polypeptides which
may be identical or
unrelated.
The individual
polypeptide chains are
known as monomers or
subunits. A dimer consist
of two polypeptides while
a tetramer has four.

13. What are
the forces
that binds
Proteins?
Hydrogen bonding,
Ionic bonding,
Co- Valent bonding,
Peptide bond

14. r
Can we
Classify
Proteins?
Yes we can
Classify the
Proteins. Let us
discuss about the
classification of
Proteins.....

15. Classification
s of Proteins
On
basis of
Functio
n
On basis of
Composition
/Solubility
On basis
of
Nutritional
level

16. Functional Classification of
Proteins Structural proteins : Keratin of hair, wool,
horn, feathers and nails ; Collagen of bone
and tendons; Fibroin of silk ; Myosin of
Muscle.
Catalytic proteins : Hexokinase, pepsin.
Transport proteins: Hemoglobin.
Hormonal proteins: Insulin, growth
hormone.
Genetic proteins : Nucleoproteins.
Defense proteins : Snake venoms.
Receptor proteins :for hormones, viruses.

17. Composition Classification of
Proteins
Simple proteins : They are composed of
only amino acid residues.
Conjugated proteins : Besides the
amino acids, these proteins contain a non-
protein moiety known as prosthetic group
or conjugating group.
Derived proteins : These are the
denatured or degraded products of simple
and conjugated proteins.

18. Nutritional classification of proteins
 Complete proteins : These proteins have
all the ten essential amino acids in the
required proportion by the human body to
promote good growth. e.g. egg albumin,
milk casein.
Partially incomplete proteins: These
proteins are partially lacking one or more
essential amino acids and hence can
promote moderate growth. e.g. wheat and
rice proteins.
Incomplete proteins: These proteins
completely lack one or more essential

19. Color Reactions of Proteins
Name of the Test Reagent Used Positive results Remarks
Biuret Test NaOH, dilute CuSO4 violet + results with polypeptides
and proteins
Xanthroproteic Test Conc. H2SO4 AA with benzene ring
(yellow)
Proteins with Tryptophan,
Tyrosine, Phenylalanine.
Million’s Test Hg(NO3) and Hg(NO2)2 Tyrosine (red) +phenolic compounts.
Sulphur Test Lead acetate, dissolved
with NaOH
Gray or black precipitate + lead sulphide, formed
as the result of the
decomposition of the
cysteine by the alkali.
Hopkins Cole Test Glyoxylic acid, sulfuric
acid
Tryptophan (violet ring) + with any compound with
indole ring
Ninhydrin Test ninhydrin Free-NH2 group (blue) + results given by NH3,
primary amines, amino
acids, peptides, and
proteins