Monomers and Polymers Explained
In biology, the concept of monomers and polymers is fundamental to understanding how large biomolecules are constructed. Monomers are individual, smaller units that can chemically bond together. When many of these single units link, they form a much larger molecule known as a polymer. This process of linking monomers to form polymers is central to the creation of many biological structures.
For instance, amino acids serve as the monomers that link together to build proteins, which are important for various cellular functions. Similarly, simple sugars, called monosaccharides, are the monomeric units that combine to form larger carbohydrate polymers, such as starch or cellulose. This repeating unit principle applies across several classes of biological macromolecules.
What Are Nucleic Acids?
Nucleic acids are among the most essential macromolecules found in all forms of life, indispensable for cellular function and heredity. The two primary types of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
Nucleic acids primarily function as the carriers of genetic information within cells. DNA, for example, serves as the master blueprint, containing the instructions necessary for the development and functioning of all living organisms. RNA plays diverse roles, including translating the genetic information from DNA into proteins.
Meet the Nucleotide: Nucleic Acid’s Building Block
The individual monomers that constitute nucleic acids are called nucleotides. Each nucleotide is a complex organic molecule composed of three distinct parts.
These three components include a nitrogenous base, a five-carbon sugar, and at least one phosphate group. The five-carbon sugar differs between DNA and RNA. DNA contains deoxyribose sugar, while RNA contains ribose sugar. The primary difference is that deoxyribose has one less oxygen atom than ribose.
The nitrogenous bases are organic molecules containing carbon and nitrogen. There are five main types of nitrogenous bases, categorized as either purines or pyrimidines. In DNA, the bases are adenine (A), guanine (G), cytosine (C), and thymine (T). In RNA, uracil (U) replaces thymine, so the bases are adenine (A), guanine (G), cytosine (C), and uracil (U).
Building the Nucleic Acid Chain
Individual nucleotide monomers link together to form a long chain, creating the nucleic acid polymer. This linkage occurs through specific chemical bonds known as phosphodiester bonds. A phosphodiester bond forms between the phosphate group of one nucleotide and the five-carbon sugar of an adjacent nucleotide. Specifically, the phosphate group attached to the 5′ carbon of one sugar connects to the hydroxyl group on the 3′ carbon of the next sugar.
This repetitive bonding creates a sugar-phosphate backbone, which forms the structural framework of the nucleic acid strand. The formation of these bonds involves a condensation reaction, where a water molecule is released. The resulting chain has a distinct directionality, referred to by its 5′ and 3′ ends. The 5′ end of a nucleic acid strand typically has a free phosphate group, while the 3′ end has a free hydroxyl group. This directionality is crucial for how genetic information is read and processed in biological systems.