Correct answer: Base pair
DNA is made up of molecules known as nucleotide, which are the building block s of nucleic acid. Each nucleotide compose of pentose sugar, phosphate group and four nitrogenous base. The four types of nitrogenous bases found in nucleotide are adenine, guanine, thymine and cytosine. In case of RNA thymine is replaced by uracil.
Each nucleotide has different sequence of base pair that allow it to link with the corresponding nucleotide and form a long chain, or sequence of amino acid which code for specific protein.