Question

Differentiate between the following :

(i) Fibrous protein and Globular protein

(ii) Peptide linkage and Phosphodiester linkage

Hint:

Compare shape and solubility for the two proteins. Then say that the peptide bond is the amide link in proteins and the phosphodiester bond is the phosphate link in nucleic acids.

Answer 1

Step 1: Understanding the Concept:
The question has two parts. Part (i) compares two shapes of protein molecules. Part (ii) compares the bonds that join the building blocks of proteins and of nucleic acids.

Step 2: Fibrous protein and Globular protein.
Fibrous proteins have polypeptide chains that run parallel to each other. The chains are held together by hydrogen bonds and disulphide bonds, so they form long fibres or sheets.
Fibrous proteins are insoluble in water. Examples are keratin (hair, nails) and myosin (muscles).
Globular proteins have chains that fold into a compact, nearly spherical shape.
Globular proteins are soluble in water. Examples are insulin and albumin.

Step 3: Peptide linkage and Phosphodiester linkage.
A peptide linkage is an amide bond, \( \mathrm{-CO-NH-} \). It forms when the \( \mathrm{-COOH} \) group of one amino acid joins the \( \mathrm{-NH_2} \) group of another amino acid with loss of water. It links amino acids in proteins.
A phosphodiester linkage joins two nucleotides. The phosphate group links the hydroxyl group on carbon-3 of one sugar to the hydroxyl group on carbon-5 of the next sugar. It links nucleotides in DNA and RNA.

Final Answer:
Fibrous proteins are thread-like and water insoluble; globular proteins are spherical and water soluble. A peptide linkage joins amino acids in proteins; a phosphodiester linkage joins nucleotides in nucleic acids.