What is Protein? What is The Structure of Protein and Building Blocks of Protein?


The most structurally and functionally working macromolecules of the cell or proteins. Proteins are unbranched polymers constructed from 22 standard alpha-amino acid. They total 20 different amino acids that differ from their side chains. They are a four-level structural organization.

  1. Primary Structure
  2. Secondary Structure
  3. Tertiary Structure
  4. Quaternary Structure 

1 – Primary Structure

The primary structure of a polypeptide is its amino acid. The amino acid is connected with a peptide bond. The structure of insulin, containing  51  amino acids was first analyzed by F sanger in1956.

2 – Secondary Structure

Protein secondary structure describes the spatial arrangement of its main -chain atoms, without regard to the positioning of its side chains. polypeptide chain may parallel in the same direction or opposite direction antiparallel.  The three-dimensional configuration is formed which terminate beta configuration. The most of the common regular secondary structures are the Alpha helix and the beta-sheet

Alpha -helix: The alpha helix a rigid, rod-like structure that form a polypedite chain twisted helix conformation. Alpha helix screw sense can be right-hand side clockwise and left-hand side anticlockwise.screw sense rotate direction helical structure rotate respect.

B -sheet: When two or more polypeptide chain segments line up side by side. The beta-strand fully extended. The distance between adjacent amino acids along beta-strand approx 3.5 angstroms. Contrast with a distance 1.5angstrom along the alpha helix.

3 – Tertiary Protein

The term tertiary structure to the unique three-dimensional conformation that globular proteins as a assume consequence of the interaction between side chains primary structure. The structure is formed by the folding polypeptide chain with the formation of a weak bond between an amino acid and side chains. these bonds are covalent bond, ionic interaction, hydrophobic interaction, van der walls force of interaction.

4 – Quaternary Structure

The nature of the formation of the bond is the same as the tertiary structure. But here the bonds occur between amino acid located in different polypeptide chains. Many proteins like hemoglobin are composed of two or more polypeptide chains. This protein called multimeric protein. The protein is a high molecular 50000 show type of configuration. Polypeptide subunits to quaternary structure and are held together by non-covalent interaction such as hydrophobic interaction, hydrogen bond, electrostatic interaction.

The molecular weight of protein: The average molecular weight a. Dimensionless quantity defined as the ratio of the particle mass to 1/12th of mass a 12C-atom and symbolized of a standard amino acid is nearer yo 128. When an amino acid participant in the formation of one molecule of water (MW=18)is removed peptide bond.

Denaturation of proteins: denaturation is a process loss their native conformation i.e normal biologically active folded conformation. It is the loss of secondary and quaternary structure of the protein which is present in the native state.it includes the break of noncovalent bond van der wall interaction, hydrophobic interaction. Denaturation in his experiment with ribonuclease that denatures the protein. Ribonuclease returns to the original structure after the removal of denaturing, the agent showing the stabilizing of protein configuration. Reagents or conditions that can cause denaturation is called denaturing agents.  Urea is most commonly used as a denaturing agent.

Example denaturing agent: strong acid or base, organic solvents, detergents, heat, heavy metal ion, reducing agent.



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