 There are four main types of ribonucleotides present in the cells and it depends upon the types of nitrogenous bases present in a ribonucleotide. You know the structure of a ribonucleotide. There are three components. One is pentose sugar, ribose sugar. The other one is phosphoric acid and the third one is nitrogenous base. The two components that is phosphoric acid and ribose sugar, they are same in all the ribonucleotides and the only difference is in the nitrogenous base. So as you know there are four types of nitrogenous bases present in a ribonucleotide. One nitrogenous base is present in one ribonucleotide but overall there are four types of ribonucleotides. So there are four types of nucleotides which are present in a ribonucleic acid. These four types they depend on the type of nitrogenous base. As you can see this colored portion, this colored portion is a nucleoside. You know this is a nucleoside because a pentose sugar and a nitrogenous base they both when they both combine they make a nucleoside and here a nitrogenous base is adenine. So this nucleoside is adenosine and when to this adenosine our phosphoric acid is attached it becomes a nucleotide. So this adenosine becomes adenylate. Let's move to the second type of ribonucleotide present in the nucleoside. Here it is guanine. So in this colored portion a guanine joins with the pentose sugar and they make a guanosine and when to this guanosine a phosphoric acid is attached it make a guanilate. So next here are two other types of ribonucleotides. Again the colored portion, this colored portion is a uridine because the nitrogenous base present here this is uracil. So to this uridine one phosphoric acid group is attached and it becomes uridylate. This is third type of ribonucleotide present in the nucleoside. The fourth and the last type of ribonucleotide is cytidylate. In our cytidylate the nitrogenous base is cytosine and this pentose sugar and this phosphoric acid is present. So when a cytosine attaches with pentose sugar it make cytidine and when to this cytidine a phosphoric acid is attached a complete nucleotide that is cytidylate is formed. So these four types of ribonucleotides are present in the ribonucleotides. Next how these ribonucleotides are joined together because I said ribonucleic acid is a polymeric compound. So many ribonucleotides join together to make a molecule. So here you can see this is one ribonucleotide and this is second ribonucleotide. So in this ribonucleotide one phosphoric acid is attached to its five carbon and this attachment is through ester linkage. So the hydroxyl group present here in this phosphoric acid it attacks to the hydroxyl group present on the pentose of next ribonucleotide. So in this way a condensation reaction takes place here a water molecule is removed and here you can see these two ribonucleotides they join together and they make a dinucleotide in which these two nucleotides are linked together through phosphodiester linkage. Why this is called phosphodiester linkage because here one phosphate group is present and this phosphate group it is linked with one pentose with the ester linkage and the second ester linkage is present here. So all this is one phosphate and two esters so it is called phosphodiester. So in this way polymeric compound consisting of many ribonucleotides are formed. So in this way many ribonucleotides they join together and they make a polymeric chain which is called a polyribonucleotide or a ribonucleic acid.