Living organisms rely on a variety of large, complex molecules known as macromolecules to perform the many processes necessary for life. These macromolecules are constructed from smaller building blocks. Among the fundamental chemical elements that compose these biological structures, nitrogen holds a significant position. It is a fundamental component of various molecules that are essential for the structure, function, and regulation of all living cells.
Proteins The Cellular Workhorses
Proteins are a major class of macromolecules that contain nitrogen, serving a vast array of functions within cells and organisms. These complex molecules are assembled from smaller units called amino acids, which are the building blocks that incorporate nitrogen into their structure. Each amino acid features a central carbon atom bonded to an amino group (-NH2), which contains nitrogen, a carboxyl group, a hydrogen atom, and a unique side chain. The diverse nature of these side chains gives proteins their varied characteristics and functions.
Amino acids link together through a chemical bond known as a peptide bond. This chain of amino acids then folds into precise three-dimensional structures, which dictate the protein’s specific role. Proteins act as enzymes, accelerating nearly all biochemical reactions in the body. They also provide structural support. Other protein functions include transporting substances, defending the body against pathogens, and transmitting signals.
Nucleic Acids The Genetic Code
Nucleic acids, which include deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), are another fundamental category of nitrogen-containing macromolecules. These molecules are responsible for storing and transmitting genetic information, guiding the construction of proteins and the overall functioning of an organism. They are polymers built from repeating units called nucleotides.
Each nucleotide consists of three main components: a five-carbon sugar, a phosphate group, and a nitrogenous base. Nitrogen is found within these nitrogenous bases—adenine (A), guanine (G), cytosine (C), and either thymine (T) in DNA or uracil (U) in RNA. DNA typically forms a double helix structure, while RNA is usually a single-stranded molecule and plays various roles in gene expression.
Nitrogen’s Broader Role in Biology
Beyond proteins and nucleic acids, nitrogen is incorporated into several other important biological molecules. Adenosine triphosphate (ATP), often referred to as the energy currency of the cell, contains nitrogen within its adenine component. Many coenzymes, which are organic molecules that assist enzymes in their functions, also contain nitrogen. Examples include nicotinamide adenine dinucleotide (NAD+) and flavin adenine dinucleotide (FAD), both of which are involved in metabolic processes. Certain vitamins, particularly some B vitamins, are also nitrogen-containing compounds.
Organisms acquire nitrogen primarily through their diet. Animals obtain it by consuming plants or other animals that have incorporated nitrogen into their tissues. Plants, in turn, absorb usable forms of nitrogen, such as nitrates and ammonium, from the soil. This usable nitrogen in the soil is often a result of the nitrogen cycle, where specialized bacteria convert abundant atmospheric nitrogen gas into forms that plants can assimilate, making it available to the entire food web.