The Basic Definition of a Nucleotide
A nucleotide is an organic molecule that serves as the monomer, or fundamental building block, of nucleic acids like DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Each nucleotide consists of three main components covalently bonded together: a five-carbon sugar, a phosphate group, and a nitrogenous base.
Components of a Nucleotide
The sugar component is either deoxyribose in DNA or ribose in RNA. The phosphate group provides the negative charge and forms the backbone of nucleic acid strands. The nitrogenous base is the variable part, responsible for coding genetic information. There are five main nitrogenous bases: adenine (A), guanine (G), cytosine (C), thymine (T) in DNA, and uracil (U) replacing thymine in RNA.
How Nucleotides Form Nucleic Acids
Nucleotides link together via phosphodiester bonds between the phosphate group of one nucleotide and the sugar of another, forming long polynucleotide chains. These chains then combine to form the double helix structure of DNA or various single-stranded structures of RNA. The specific sequence of nitrogenous bases along these chains determines the genetic code.
Beyond Genetic Information: Other Roles of Nucleotides
While best known for their role in genetic material, nucleotides also play other vital functions. For example, adenosine triphosphate (ATP) is a critical nucleotide derivative that acts as the primary energy currency of the cell, storing and releasing energy for metabolic processes. Other nucleotides function as coenzymes in various biochemical reactions, signaling molecules, and regulators of enzyme activity.