Chargaff’s Rule
Chargaff’s rule is a fundamental principle in the study of DNA. It states that the amount of adenine (A) always equals the amount of thymine (T) in the DNA of any given species, and likewise, the amount of guanine (G) always equals the amount of cytosine (C). This means that the base composition of DNA is consistent within a single organism, but can vary between different species.
This rule was first observed by Erwin Chargaff, an Austrian biochemist, in the 1940s. It was a crucial discovery that contributed to the eventual unraveling of the structure of DNA by Watson and Crick in 1953. Understanding Chargaff’s rule is important because it helps explain the complementary nature of the two strands of DNA and the mechanism of DNA replication. It also serves as the basis for understanding the genetic code and how DNA carries and transmits genetic information.
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.