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Chemistry - JEE mains PYQ

Q. Two nucleotides are joined together by a linkage known as: (JEE Main 2024)

Options:

1. Phosphodiester linkage

2. Glycosidic linkage

3. Disulphide linkage

4. Peptide linkage

Correct Answer: 1. Phosphodiester linkage

Phosphodiester linkage between nucleotides

Explanation:

A nucleotide consists of three components: nitrogenous base + pentose sugar + phosphate group.

When two nucleotides join to form DNA or RNA, the 3′-OH group of one sugar reacts with the 5′-phosphate group of the next nucleotide.

This bond is called a phosphodiester linkage, and it forms the sugar–phosphate backbone of nucleic acids.

Why other options are incorrect:

  • Glycosidic linkage: connects base to sugar (within one nucleotide)
  • Disulphide linkage: found in proteins (between cysteine residues)
  • Peptide linkage: joins amino acids in proteins

JEE Tip: DNA & RNA → Phosphodiester bond Proteins → Peptide bond Carbohydrates → Glycosidic bond

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