Question

What covalent bond links nucleotides together?

Answer 1

Hint: Covalent Bonds are generally formed by equal sharing of electrons from both the participating non-metallic atoms. Covalent as is sharing of electrons is generally between which are not able to lose an electron or are not able to accommodate an electron due to high ionization energy or low electron affinity.

Complete step by step answer:
 A nucleotide contains a cyclic pentagonal ring having O instead of the fifth carbon, 4th carbon has a $C{H_2}$ attached to a 0 which is in turn attached to a phosphate group. The third and second carbon on the sugar ring has $ - OH$ attached to them. The 1st carbon of the ring has benzene attached to it.
Now the question asks how the nucleotides form the bond and of what nature.

Now to form a bond between two nucleotides is the condensation process or dehydration process in which a water molecule comes out. Now on condensation, the $ - OH$ on the 3rd carbon of one of nucleotide atom reacts with the $ - OH$ on the phosphate group, the ${H^ + }$ from one of the $ - OH$ attacks the other and therefore forming $ - {(O{H_2})^ + }$, which breaks off from the compound and the O forms a diester bond with P and C, resulting in a covalent bond.

Nucleotides has a diester covalent bond formed between them on dehydration or condensation.

Note: Nucleotides are organic molecules consisting of a sugar ring (nucleoside) and a phosphate group. They act as monomeric units to DNA and RNA, the building code of our body.