What is the building block of nucleic acids?

The building blocks of nucleic acids are called nucleotides. Nucleotides are organic molecules that consist of three main components: a sugar molecule, a phosphate group, and a nitrogenous base.

1. Sugar: The sugar component in nucleotides is either ribose or deoxyribose. These sugars have a five-carbon ring structure and are known as pentoses. In RNA (ribonucleic acid), the sugar is ribose, while in DNA (deoxyribonucleic acid), the sugar is deoxyribose. The difference between the two sugars lies in the presence or absence of a hydroxyl group (-OH) on the 2' carbon of the sugar ring.

2. Phosphate Group: The phosphate group is a functional group consisting of a phosphate atom bonded to four oxygen atoms. It provides the acidic nature of nucleotides and plays a crucial role in the structure and function of nucleic acids. Multiple nucleotides can link together through phosphodiester bonds, forming long chains called polynucleotides or nucleic acids.

3. Nitrogenous Base: The nitrogenous base is the third component of nucleotides and can be classified into two types: purines and pyrimidines. Purines include adenine (A) and guanine (G), while pyrimidines include cytosine (C), thymine (T, found only in DNA), and uracil (U, found only in RNA). Nitrogenous bases are responsible for the genetic information carried by DNA and RNA. They form hydrogen bonds with complementary bases, which contribute to the stability of the DNA double helix or the RNA secondary structure.

When nucleotides combine, they form a polymer through phosphodiester linkages between the sugar of one nucleotide and the phosphate group of another. This sequential arrangement of nucleotides in nucleic acids forms the genetic code that carries information for the synthesis of proteins and other cellular processes.