In a sample of DNA extracted from a eukaryotic cell, the primary biomolecules present are nucleic acids, specifically deoxyribonucleic acid DNA . DNA is a long, double-stranded polymer composed of repeating units called nucleotides. Each nucleotide consists of three components: a deoxyribose sugar, a phosphate group, and a nitrogenous base. The chemical structures of these components are as follows:1. Deoxyribose sugar: Deoxyribose is a five-carbon sugar pentose with the chemical formula C5H10O4. It has a ring structure with four carbons and one oxygen atom in the ring. The 2' carbon of deoxyribose lacks an oxygen atom, distinguishing it from ribose sugar found in RNA.2. Phosphate group: The phosphate group has the chemical formula PO4^3-. It is an inorganic molecule consisting of one central phosphorus atom surrounded by four oxygen atoms in a tetrahedral arrangement. The phosphate group is negatively charged, contributing to the overall negative charge of the DNA molecule.3. Nitrogenous bases: There are four different nitrogenous bases in DNA: adenine A , guanine G , cytosine C , and thymine T . These bases can be divided into two categories: purines adenine and guanine and pyrimidines cytosine and thymine . - Adenine: Adenine is a purine base with the chemical formula C5H5N5. It has a double-ring structure consisting of a six-membered pyrimidine ring fused to a five-membered imidazole ring. - Guanine: Guanine is also a purine base with the chemical formula C5H5N5O. It has a double-ring structure similar to adenine, but with an additional oxygen atom in the six-membered pyrimidine ring. - Cytosine: Cytosine is a pyrimidine base with the chemical formula C4H5N3O. It has a single-ring structure consisting of a six-membered pyrimidine ring with nitrogen atoms at positions 1 and 3. - Thymine: Thymine is a pyrimidine base with the chemical formula C5H6N2O2. It has a single-ring structure similar to cytosine, but with additional methyl and carbonyl groups attached to the pyrimidine ring.The nucleotides are linked together by phosphodiester bonds, which connect the 3' carbon of one deoxyribose sugar to the 5' carbon of the next deoxyribose sugar through a phosphate group. The DNA double helix is formed by two complementary strands running in opposite directions antiparallel and held together by hydrogen bonds between the nitrogenous bases. Adenine pairs with thymine A-T through two hydrogen bonds, and guanine pairs with cytosine G-C through three hydrogen bonds. This specific base pairing is known as Watson-Crick base pairing and is crucial for the accurate replication and transcription of genetic information.