Q. Which are nucleotides "portions" that to bind in the formation of nucleic acids? What is meant by the 5' and 3' extremities of the nucleic acids?
The phosphate group of one nucleotide binds to the pentose of the other nucleotide and so on to make the polynucleotide chain.
Each extremity of a RNA or DNA chain can be distinguished from the other extremity according to their terminal chemical entity. The phosphate-ended extremity is known as 5'-extremity and the pentose-ended extremity is called 3'-extremity. So RNA or DNA chains can be run along the 3'-5' way or along the 5'-3' way. These ways are significant in several biological functions of RNA and DNA since some reactions specifically occur following one way or the other way.