Question

What are the four basic units of DNA?

Answer 1

Hint: During his research on white blood cells in 1869, Swiss biologist Johannes Friedrich Miescher recognized and identified DNA for the first time. James Watson and Francis Crick used experimental data to discover the double helix structure of a DNA molecule.

Complete answer:
Deoxyribonucleic acid (DNA) is a molecule made up of two polynucleotide chains that coil around each other to form a double helix and carry genetic instructions for all known organisms and viruses' development, function, growth, and reproduction.
Nucleic acids include DNA and ribonucleic acid (RNA). Nucleic acids are one of the four major types of macromolecules that are required for all known forms of life, alongside proteins, lipids, and complex carbohydrates (polysaccharides). As they are made up of smaller monomeric units called nucleotides, the two DNA strands are called polynucleotides. Each nucleotide is made up of a sugar called deoxyribose, a phosphate group, and one of four nitrogen-containing nucleobases (cytosine [C], guanine [G], adenine [A], or thymine [T]).
Covalent bonds (known as the phospho-diester linkage) between the sugar of one nucleotide and the phosphate of the next nucleotide link the nucleotides together in a chain, resulting in an alternating sugar-phosphate backbone. The nitrogenous bases of the two polynucleotide strands are linked together with hydrogen bonds according to base-pairing rules (A with T and C with G).

Thus, The four bases of DNA are: Adenine (A), Guanine (G), Cytosine (C), Thymine (T)
and basic unit of DNA is nucleotides

Note:
DNA is organized into long structures called chromosomes within eukaryotic cells. These chromosomes are duplicated in the process of DNA replication before normal cell division, providing a complete set of chromosomes for each daughter cell. The majority of DNA in eukaryotic organisms (animals, plants, fungi, and protists) is stored as nuclear DNA in the cell nucleus, with some stored as mitochondrial DNA in the mitochondria.