Question

What forms the backbone of a polynucleotide strand of nucleic acid?

Answer 1

Nucleotides are the building block or the monomeric unit of the nucleic acid-DNA or RNA. The chain of nucleotides is known as the polynucleotide chain. Two nucleotides are linked together by the phosphodiester bond.

Complete answer:
The nucleic acid-DNA and RNA is made up of repeating units of nucleotides. The nucleotide and the phosphate molecule together form the nucleotide. The nucleoside consists of ribose sugar and a nitrogenous base. The nucleotides form the basic unit of life DNA and RNA which is essential in all living forms. The nucleotides are made up of three elements- ribose 5 carbon sugar, phosphate and a nitrogenous base. The detailed structure is as follows.

- Nitrogenous bases: The nitrogenous bases are the bases that are made up of nitrogen. They are 5 in number. Adenine, guanine, cytosine and thymine form DNA and uracil form RNA.
- Ribose sugar: It is a 5-carbon ring that is deoxyribose in the case of DNA and ribose in the case of RNA. In the case of DNA, the hydroxyl group is not present in the 2’ carbon.

The sugar and phosphate molecule forms the backbone of the nucleic acid in which the phosphodiester bond is formed in between the sugar base of one nucleotide and the phosphate of the other.

Note: The properties of phosphodiester bonds are-
- They are the backbone of nucleic acid.
- They are negatively charged at pH 7.
- The 3’ carbon of one sugar forms the bond to the 5’phosphate of the adjacent sugar.
- It helps in maintaining the integrity of the genetic code.