![]() As a result, one DNA strand has 3′ end with terminal hydroxyl group and the second strand has 5′ end having a terminal phosphate group. the direction of one strand is opposite to the other and thus two strands are antiparallel to each other. Because of these asymmetric bonds, each DNA strand of the helix has a unique direction i.e. The third carbon of 2′ deoxyribose sugar molecule is attached to the phosphate group by phosphodiester bond to the fifth carbon atom of adjacent 2′ deoxyribose molecule. Each strand of polynucleotide consists of sugar-phosphate backbone made up of alternating 2′ deoxyribose and phosphate groups. These two long strands are intertwined (coiled) in the shape of a double helix which have the unique ability to wind and unwind to facilitate the duplication process. DNA, in the form of plasmids, can also be located extrachromosomally both in prokaryotes and few eukaryotes such as yeast.ĭNA consists of two polymer chains made up of nucleotides. However, the cells of eukaryotic organisms contain DNA in their nucleus and in other organelles such as mitochondria or chloroplasts. In prokaryotes, DNA is loosely packed in the cytoplasm and lacks distinct nuclear membrane. The major role of DNA in a cell is to store the genetic information or instructions that are essential for carrying out various cellular functions like synthesis of biomolecules including RNA for the development of living cell. The double helical structure of DNA was proposed by James Watson and Francis Crick in 1953 and nine years later, they along with Maurice Wilkins in 1962 received the Nobel Prize for this discovery. However, thymine is found only in DNA and uracil only in RNA. DNA and RNA contain adenine, guanine and cytosine. The members of purines and pyrimidines share a similar structure, but differ in their side groups. 4.2) are Cytosine (C), Thymine (T) and Uracil (U). ![]() 4.1) are Adenine (A) and Guanine (G) and Pyrimidines (Fig. They are polyfunctional bases having at least one N-H site for attaching with one organic substitute. Nitrogenous bases occurring in nucleic acids fall into two categories, viz., monocyclic bases (comprising of a hexagonal aromatic ring) called pyrimidines and bicyclic bases (comprising of one hexagonal and one pentagonal aromatic ring) called purines. Nucleic acids are basically the polymer molecules of nucleotides which are essentially made up of three basic components, a heterocyclic nitrogenous base, a pentose sugar and a phosphate group. The structure and functions of these molecules are described below: There are two types of nucleic acids, Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA). Nucleic acid structure is surprisingly simple, despite of its importance in cellular functions. These universal molecules were first discovered by Friedrich Miescher in 1871. Nucleic acids, particularly DNA, are the macromolecules considered to be the hereditary material which store the genetic information used in the development and functioning of all known living organisms. NUCLEIC ACIDS – STRUCTURE AND FUNCTION OF DNA AND RNA
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