In a mRNA the nucleotides are linked to one another by:

Question

Accepted Answer

The correct option is 4: Phosphodiester bonds

Phosphodiester bonds are the strong, covalent linkages that form the crucial sugar-phosphate backbone of all nucleic acid molecules, including messenger RNA (mRNA). As you know, a nucleic acid is a long polymer chain made up of repeating monomer units called nucleotides. Each nucleotide is composed of a phosphate group, a ribose sugar (in RNA), and a nitrogenous base. The phosphodiester bond is formed through a condensation reaction where the phosphate group attached to the 5' carbon of one ribose sugar chemically links to the hydroxyl (-OH) group on the 3' carbon of the *next* ribose sugar. This creation of a 5' to 3' linkage is what gives the mRNA strand its linear directionality and its fundamental, resilient structure, enabling it to safely carry genetic information from the nucleus to the ribosome.

The incorrect option is 1: Hydrogen bonds
Hydrogen bonds are weak, non-covalent interactions that are essential for stabilizing the *secondary* and *tertiary* structures of nucleic acids, not the primary linear chain. In the famous double-helical structure of DNA or in localized hairpins within RNA, these bonds form horizontally between complementary nitrogenous bases (Adenine to Uracil/Thymine, Guanine to Cytosine). Because mRNA is predominantly a single-stranded molecule, it does not rely on extensive base-pairing, and hydrogen bonds are only used to stabilize temporary, local structures like stem-loops. Therefore, hydrogen bonds connect one strand to another, or one part of a strand to another part of the same strand, but they do not link successive nucleotides along the backbone.

The incorrect option is 2: Van-der-Waals forces
Van-der-Waals forces are extremely weak, transient, non-specific attractive forces that arise from temporary fluctuations in electron distribution. In nucleic acids, these forces contribute significantly to the *stacking* interactions that occur between the flat, aromatic nitrogenous bases in the interior of the helical structure. These stacking interactions are crucial for adding stability to the overall three-dimensional shape of the molecule. However, they are non-covalent and are far too weak to be the primary chemical bond holding the sequential nucleotides together in the stable, permanent linear polymer chain.

The incorrect option is 3: Glycosidic bonds
Glycosidic bonds (specifically N-glycosidic bonds) are indeed strong covalent bonds found in nucleic acids, but their location is internal to the nucleotide monomer, not between monomers. This bond is responsible for connecting the nitrogenous base (Adenine, Uracil, Cytosine, or Guanine) to the C-1' carbon of the ribose sugar to form the nucleoside portion of the molecule. Therefore, while a glycosidic bond is necessary to build a single nucleotide, it does not participate in the polymerization process of linking one complete nucleotide unit to the next to create the long mRNA strand.