 Dear students, in this module I am going to discuss the chemical composition of RNA, RNA or ribonucleic acids. This is another major type of nucleic acid present in the cells. It is also a polymeric compound just like DNA. As you know DNA is made up of deoxyribonucleotides but here RNA, RNA is made up of ribonucleotides. So ribonucleotide is the monomer of ribonucleic acids. So each ribonucleotide is made up of three components and these three components include our ribose sugar, our nitrogenous base and our phosphoric acid. So these three components they join together and they make a ribonucleotide. And different ribonucleotides they join together and they make a polynucleotide which is ribonucleic acid. Here this is the first component of ribonucleic acid and this is our pentose sugar. Here the pentose sugar is a ribose. You know in DNA this sugar is also present but this is present in its derivatized form and that form is deoxyribose sugar. You can see at carbon number two an OH group is present here but in case of deoxyribose sugar only hydrogen was present, oxygen was removed. So here the pentose sugar is ribose instead of deoxyribose. This is first component of our ribonucleic acid. The second component of ribonucleic acid is the nitrogenous base. There are mainly two types of nitrogenous bases present in the ribonucleic acid and these are purines and pyrimidines. Two types of purine bases that is adenine and goanine are present in the ribonucleotide. These two bases adenine and goanine were also present in the deoxyribonucleotide. The next two types of bases that is pyrimidines and these are cytosine and uracil. Here you can see a difference. In case of DNA, uracil is not present and instead thymine was present in DNA molecule but here instead of thymine, uracil is present. So overall there are five types of nitrogenous bases. These are adenine, goanine, cytosine, thymine and uracil. Thymine is only present in DNA molecules while uracil is only present in RNA molecules. The third component of ribonucleotide is a phosphoric acid. Phosphoric acid you can see it has three hydroxyl groups and these hydroxyl groups they have ability to make ester linkages with the hydroxyl groups present on the pentose sugar either ribose or deoxyribose. So ideally it can make three ester linkages but normally in a poly nucleotide chain it makes this phosphoric acid makes two ester linkages. So this is a complete ribonucleotide. It consists of all the three components that is nitrogenous base, a pentose sugar and a phosphoric acid. These three components are joined together and they make a ribonucleotide and this ribonucleotide by combining with other ribonucleotides it make a ribonucleic acid.