Proteins are composed of chains of amino acids that are linked together by peptide bonds. The amino acid composition determines a protein's properties. There are four levels of protein structure - primary, secondary, tertiary, and quaternary. The primary structure is the amino acid sequence. Secondary structure involves hydrogen bonding that forms alpha helices and beta sheets. Tertiary structure describes the three-dimensional folding of the polypeptide chain. Quaternary structure results from interactions between subunits in multimeric proteins.

1. K

2. Proteins
 Proteins are numerous large, complex naturally
produced molecules composed of one or more long
chains of amino acids, in which the amino acid groups
are held together with peptide bond.

3. Proteins properties depends upon
the amino acid composition.
Amino acids are the building blocks of proteins.
Amino acids can be classified by the presence of R
group.

5. Function of R groups
Aromatic R group
• Tryptophan
Provide hydrophobicity
• form hydrogen bonding
Non-polar R group
•Ala,Val,Leu And Iso
•Pro
Stabilize the protein
Side chains cluster together
and stabilize
Provide rigidity
Polar uncharged R group
•Cysteine
Make them soluble in water
make disulfide bond
Negatively charged R group Provide negative charge
Positively charged R group Provide positive charge

6. Ionization behaviour
The acid-base behavior of a peptide can be predicted
from its free alpha amino and alpha carboxyl groups
and the nature and number of its ionisable R groups.
Isoelelectric point(PI)-It is the pH at which amino acid
have no net charge, thus it is electrophoretically
immobile.

7.  In solution amino acid exist in zwitter ionic form.
Which provide them physical properties
characteristics of ionic compounds. i.e., high melting
point, water solubility and low solubility in organic
solvents.
 Ionisation pattern is different for different amino acid

8.  There are more ionisable groups in amino acids other than
carboxyl and amino group.
 groups include a phenolic group (tyrosine), guanidino
group (arginine), imidazolyl group (histidine) and
sulphydryl group (cysteine) .
 ionisable groups are on the outside of the molecule,
 can interact with the surrounding aqueous medium some
located within the structure may be involved in
electrostatic attractions that help to stabilise the three-
dimensional structure of the protein molecule

9.  These properties use for electrophoretic and ion
exchange chrometographic seperation of mixture of
amino acids.
 at the isoelectric protein has minimum solubility,
since it is the point at which there is the greatest
opportunity for attraction between oppositely charged
groups of neighboring molecules and consequent
aggregation and easy precipitation.

10. Shape
 Enzymes, hormones, structural protein, receptor,
antibody all are protein .but how they are distinct from
each other?
 This is of because of their structure.
 There are four levels of protein structure.

12. Other interaction for protein
folding

13. Protein denaturation
 When temperature of a protein solution is increased there
is breaking of weak interaction (primarily hydrogen bonds)
resulting in denaturation of protein.
 denaturation: Partial or complete unfolding of the
specific native conformation of a polypeptide chain,
such. that the function of the molecule is lost
 Proteins can also be denatured by extremes of pH, by
certain miscible organic solvents such as alcohol or
acetone, by certain solutes such as urea and guanidine
hydrochloride, or by detergents. Each of these denaturing
agents represents a relatively mild treatment in the sense
that no covalent bonds in the polypeptide chain are broken

14. Solubility in water
 Typically a protein contains multiple charged group, so
its solubility depends on the concentrations of
dissolved salts , the polarity of solvent, the pH and the
temperature.
 The solubility of a protein at low concentration
increase as salt is added, a process called Salting in.
 The additional ion shield the protein charged group,
thereby weakening the attractive force between
individual protein molecules.

15.  However ,when more salt is added , the solubility of
protein decrease. This Salting out effect is primarily a
result of competition between added salt ions and
protein molecules for water.
 At very high salt concentration so many of the added
ions are solvated that there is significantly less bulk
solvent available to dissolve other substance including
protein.
 Since protein precipitates at different salt
concentration s, salting out is the basis of most
commonly used protein purification procedure.

16.  (a) Primary structure. The primary structure of a protein
is a sequence of amino acids linked together by peptide
bonds, forming a polypeptide.
 Each type of protein also has a unique amino acid
sequence. And the function of a protein depends on its
amino acid sequence so if the primary structure is altered ,
the function of that protein also be change.
 (b) Secondary Structure. The secondary structure of a
protein describes local regions of structure that result
from hydrogen bonding between NH and CO groups
along the polypeptide backbone. These local interactions
result in two major structural patterns, referred to as the
helix and sheet conformations

17.  an a helix is spiral in shape, consisting of a backbone
of amino acids linked by peptide bonds with the
specific R groups of the individual amino acid residues
jutting out from it.
 Another form of common secondary structure in
proteins is the beta sheet, this structure is an extended
sheet like conformation with successive atoms in the
polypeptide chain located at the “peaks” and “troughs”
of the pleats. The R groups of successive amino acids
jut out on alternating sides of the sheet. Because the
carbon atoms that make up the backbone of the
polypeptide chain are successively located a little
above and a little below the plane of the b sheet, such
structures are sometimes called beta pleated sheets.

18. (c) Tertiary structure is the complete three-dimensional
structure of a polypeptide chain. There are two general
class of proteins based on tertiary structure: fibrous and
globular.
 Fibrous proteins, which serve mainly structural roles,
have simple repeating elements of secondary structure.
 Globular proteins have more complicated tertiary
structures, often containing several types of secondary
structure in the same polypeptide chain..
(d)Quaternary structure results from interactions
between the subunits of multisubunit (multimeric)
proteins or large protein assemblies . Some multimeric
proteins have a repeated unit consisting of a single subunit
or a group of subunits