Formation of Nucleotide Chain
A polynucleotide chain, such as DNA or RNA, is composed of three components: a nitrogenous base, a pentose sugar (ribose in RNA and deoxyribose in DNA), and a phosphate group. There are two types of nitrogenous bases: purines (adenine and guanine) and pyrimidines (cytosine, uracil, and thymine). Cytosine is found in both DNA and RNA, while thymine is present only in DNA, and uracil is present in RNA in place of thymine. A nitrogenous base is connected to the 1′ carbon of the pentose sugar through an N-glycosidic linkage to form a nucleoside, such as adenosine or deoxyadenosine, guanosine or deoxyguanosine, cytidine or deoxycytidine, and uridine or deoxythymidine. When a phosphate group links to the 5′ carbon of a nucleoside through a phosphodiester linkage, a nucleotide (or deoxynucleotide, depending on the sugar present) is formed. Two nucleotides are linked through a 3′-5′ phosphodiester linkage to form a dinucleotide. More nucleotides can be linked to form a polynucleotide chain. The resulting polymer has a free phosphate moiety at the 5′-end of the sugar and a free 3′-OH group at the other end. The backbone of a polynucleotide chain is formed by sugars and phosphates, with nitrogenous bases projecting from the backbone.
Polynucleotide Chain
A polynucleotide chain is a long chain of nucleotides, which are the building blocks of DNA and RNA molecules. Nucleotides are composed of a sugar molecule, a phosphate group, and a nitrogenous base. The nitrogenous base can be one of four types: adenine (A), guanine (G), cytosine (C), or thymine (T) in DNA, or uracil (U) in RNA. The sequence of these nitrogenous bases determines the genetic information stored in DNA and RNA and ultimately governs the structure and function of all living organisms. The polynucleotide chain is held together by phosphodiester bonds between the sugar and phosphate groups, and the nitrogenous bases extend from the sugar-phosphate backbone, forming the rungs of the DNA or RNA ladder. Understanding the properties and functions of polynucleotide chains is fundamental to the study of genetics and molecular biology.