Hence the process of DNA replication is said to be a semi-conservative one. Each of the two resultant, identical DNA molecules is composed of one old and one new strand of DNA. In response to the molecular cues received during cell division, these molecules initiate DNA replication, and synthesize two new strands using the existing strands as templates. The process of DNA replication is a complex one, and involves a set of proteins and enzymes that collectively assemble nucleotides in the predetermined sequence. The A = T and G ≡ C base pairs form the rungs of this helical ladder. This forms a helical structure instead of a straight ladder. The DNA twists at specific lengths due to the bonding angles of the DNA backbone molecules. Adenine pairs with thymine through a double bond (A = T), whereas guanine pairs with cytosine through a triple bond (G ≡ C). These strands are attached to each other through hydrogen bonding that occurs between purines and pyrimidines of opposite strands. One strand runs in the 5′ → 3′ direction, while the other runs in an anti-parallel direction of 3′ → 5′. The DNA double helix comprises two complementary strands that run anti-parallel to each other. Each strand has a 5′ phosphate end and a 3′ hydroxyl end. The sugar moieties and the phosphate groups form the backbone of each DNA strand. The phosphate group of one nucleotide and the hydroxyl group of the adjacent nucleotide are connected through a phosphodiester bond. These nucleotides are linked through their phosphate groups and sugar moieties to form a single strand of the DNA molecule. On the other hand, adenine and guanine are purines, which are two-ringed molecules comprising a pyrimidine ring and an imidazole ring. These four nucleotides (and their respective nitrogenous bases) are:Ĭytosine and thymine are pyrimidines, a type of six-membered heterocyclic molecules. There are four types of nucleotide molecules depending on the type of nitrogenous base attached. The building blocks of a DNA are molecules called nucleotides, that consists of a deoxyribose sugar (a 5-carbon sugar), a nitrogenous base attached to the sugar, and a phosphate group. Given below is a brief account of the DNA structure as well as the steps through which a DNA molecule makes copies of itself with an extraordinary accuracy. But even more enthralling is its ability to self-replicate and generate another molecule similar to itself. The simple chemical code of the DNA molecule gives rise to the immense complexity of all living organisms. With this foundation, and the research by several scientists like Rosalind Franklin, the structure of this molecule was finally deciphered by James Watson and Francis Crick. It took several interesting experiments by Frederick Griffith, Avery, MacLeod, McCarty, Alfred Hershey, Martha Chase etc., to discover that DNA is the hereditary material. This is equivalent to copying 100 dictionaries (with 1000 pages each) word to word, page to page, and symbol to symbol, with only one mistake!ĭeoxyribonucleic acid or DNA is the fascinating molecule that stores and passes all the necessary information from one generation to another. Less than one mistake occurs while copying a billion nucleotides.
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