proteins with its detailed structures.pptx

proteins

1. PROTEIN & ITS STRUCTURE

2. Classification Primary structure Secondary structure Tertiary structure Quaternary structure

3. Protein Protein is generally used for a polypeptide containing More than 50 amino acids

4. Peptide bond Formation of peptide bond: The amino group of amino acid combine with the carboxyl Group of another amino acids then, a peptide bond is formed.

5. Characteristics of peptide bonds The peptide bond is rigid and planar with partial
double bond in character. It generally exists intrans configuration. Both –C=O and –NH groups of peptide bonds are polar and are involved in hydrogen bond formation

6. Primary structure The Primary structure of proteins is the exact ordering of amino acids forming their chains. The exact sequence of the proteins is very important as it determines the final fold and therefore the function of the protein.

7. Secondary structure The proteins do not exist in just simple chains of polypeptides. These polypeptide chains usually fold due to the interaction between the amine and carboxyl group of the peptide link. They are found to exist in two different types of structures α – helix and β – pleated sheet structures. .

8. Alpha– Helix: A-Helix is the most common spiral structure of protein 1. The a-helix is a tightly packed coiled structure with amino acid side chain 2. The a-helix is stabilized by extensive hydrogen bonding.lt is formed between H atom attached to pep tide N, and O atom attached to peptide. The hydrogen bonds are individually weak. 3. All the peptide bonds, except the first and
last in a polypeptide chain, participate in
hydrogen bonding.
4. Each turn of a-helix contains 3.5 amino
acids and travels a distance of 0.54 nm. The
spacing of each amino acid is 0.15 nm.
5. a-Helix is a stable conformation formed
spontaneously with the lowest energy.

9. Beta pleated sheet In this arrangement, the polypeptide chains are stretched out beside one another and then bonded by intermolecular H-bonds This is the second type of structure (hence alpha
after beta) proposed by Pauling and Corey. Beta -Pleated sheets (or simply beta-sheets) are
composed of two or more segments of fully
extended peptide chain

10. Supersecondary structure The type of protein which is intermediate between the secondary and tertiary structure is called Supersecondary structure . It is connected through loops & bend at specific pattern This is the second type of structure (hence p after a) proposed by Pauling and Corey. p-Pleated sheets (or simply p-sheets) are composed of two or more segments of fully extended peptide chain

11. Tertiary structure The tertiary structure of proteins represents overall folding of the polypeptide chains, further folding of the secondary structure.
It gives rise to two major molecular shapes called fibrous and globular.
The main forces which stabilize the secondary and tertiary structures of proteins are hydrogen bonds, disulphide linkages, van der Waals and electrostatic forces of attraction.

12. Quaternary structure The spatial arrangement of various tertiary structures gives rise to the quaternary structure. Some of the proteins are composed of two or more polypeptide chains referred to as sub-units. The spatial arrangement of these subunits with respect to each other is known as quaternary structure. Example Hemoglobin Insulin

13. Chemical properties Reactions due to –COOH group 1. Amino acids form salts (- COONa ) with
bases and esters (-COOR’) with alcohols.
2. Decarboxylation: Amino acids undergo
decarboxylation to produce corresponding
amines.
R-CH-COO ----+ R-CH2 + CO2
This reaction assumes significance in the
living cells due to the formation of many
biologically important amines. These
include histamine, tyramine

14. Properties 3. Reaction with ammonia: The carboxyl
group of dicarboxylic amino acids react
with NH3 to form amide
Aspartic acid + NH, ------; Asparagine
Glutamic acid + NH. ------+Glutamine

15. Reactions due to –NH2 group 4. The amino groups behave as bases and
combine with acids (e.g. HCI) to form
salts (- NHiCl -).
5. Reaction with ninhydrin : The amino
acids react with ninhydrin to form a
purple, blue or pink colour complex
( Ruhemann’s purple).
Amino acid + Ninhydrin ---+ keto acid + Nh3+Coz+Hydrindantin Hydrindantin + NH: + Ninhydrin -----+ Ruhemann’s purple

16. 6. Colour reactions of amino acids : Amino
acids can be identified by specific colour 7. Transamination : Transfer of an amino
group from an amino acid to a keto acid
to form a new amino acid is a very
important reaction in amino acid
metabolism
8. Oxidative deamination : The amino acids
undergo oxidative deamination to liberate free ammonia.

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