What is a nucleotide?

A nucleotide is defined as the basic building block of nucleic acids, such as DNA and RNA. Each nucleotide consists of three key components: a sugar molecule, a phosphate group, and a nitrogenous base. This unique combination allows nucleotides to play a crucial role in storing and transmitting genetic information.

In DNA, for example, the nitrogenous bases (adenine, thymine, cytosine, and guanine) pair in specific ways to encode genetic instructions, while the sugar and phosphate backbone forms the structural framework of the DNA helix. Because of this structure, nucleotides are essential for processes like DNA replication and protein synthesis.

Other answer choices refer to concepts that are not related to the definition of a nucleotide. Proteins play very different roles in cellular functions, gene expression involves complex biological processes influenced by various factors but is not the same as a nucleotide, and structures made entirely of proteins do not encompass the components or functions of a nucleotide. Understanding the makeup and function of a nucleotide is fundamental to grasping how genetic information is encoded and expressed in living organisms.