A repeating unit of a very large DNA molecule is made up of

DNA (deoxyribonucleic acid) is a polymer, meaning it is built from many repeating smaller units linked together in a long chain. The repeating unit of DNA is called a nucleotide.

Each nucleotide consists of three components:

• A phosphate group
• A five-carbon sugar called deoxyribose
• A nitrogenous base (adenine, thymine, guanine, or cytosine)

While a phosphate group, a nitrogenous base, and deoxyribose sugar are each individual components of a nucleotide, none of them alone constitutes the repeating unit of DNA. The repeating unit is the complete nucleotide, which contains all three components bonded together. Nucleotides are joined by phosphodiester bonds between the phosphate group of one nucleotide and the sugar of the next, forming the sugar-phosphate backbone of the DNA strand.

When revising this topic, remember to distinguish between the monomer (nucleotide) and its individual parts. The question asks for the repeating unit - that is always the complete monomer, not one of its sub-components.