, Diagnosis an-&& of Shrimp Diseases - Central Institute of ...

which serve as the inajor building blocks of DNA macromolecule. They are all similar exceptfor the nitrogenous base. Each nucleotide is named after the base. The purine derivatives areadenine (A) and guanine (G) while the pyrimidine derivatives are cytosine (C) and thymine(T). Similarly, four different ribonucleotides are the building blocks for the RNA. They arethe purine bases adenine and guanine. The pyrimidine bases are cytosine and uracil (U). Thepentose sugar is different in DNA and RNA, DNA contains 2-deoxy ribose sugar, while RNAcontains ribose sugar.Nucleic Acids exist in different formsNucleic acids exist in two major types, nameiy DNA and RNA. Though DNA exists in onetype they exist in different forms, as linear, circular, single stranded and double strandedforms. On the contrary mostly RNA exists as single stranded form. There are three types ofRNA present in a living cell- messenger RNA (mRNA), Ribosomal RNA (rRNA) andtransfer RNA (tRNA). Even though RNAs are single stranded, they forin extensive secondarystructures as in the case of tRNAs and rRNAs. Messenger RNAs of eukaryotic cells areunique that they contain long stretches of poly (A) sequences at the 3' ends (the carbon atomsare numbered by adding prime to the number, for ego 2nd carbon atom in the sugar is writtenas 2', 3rd as 3' etc). In general DNA contains the genetic information; however, in certainviruses RNA contains the genetic information.DNX4ZNA are formed by covalent links of Deoxy/Oxy ribonucleotidesA nucleic acid is polynucleotide - that is a polymer consisting of nucleotides. The pentosesugar is a cyclic five carbon ribose sugar in case of RNA and 2'deoxyribose sugar in the caseof DNA. A purine or pyrimidine base is attached to the 1' carbon atom of the pentose sugar byan N-glycosidic bond. A phosphate is attached to the 5' carbon of the sugar by phosphoesterbond. It is this phosphate which gives the strong negative charge for the nucleotides and thenucleic acids. This property is used in agarose gel electrophoresis of nucleic acids. Thenucleotides in nucleic acids are covalently linked by a second phosphoester bond that joinsthe 5' phosphate of one nucleotide and the 3' OH group of adjacent nucleotide. This phosphateplus its bonds to the 3' and 5' carbon atoms is called a phosphodiester bonds.