Definition of Directionality



In the terms of molecular biology, the directionality is known as the end-to-end orientation of the single-stranded DNA or RNA. It is a convention to name the carbon atoms belonging to the nucleotide and sugar ring as 5’ end and 3’ end. This convention of naming the carbons is very significant as the nucleic acids can only be synthesized in the direction of 5’ to 3’.

 


The polymerase either DNA or RNA tend to add the new nucleotides to 3’-OH group. Along the strand of the nucleic acid, the positions of the genes and that of the binding sites for protein are generally regarded as upstream if they are towards 5’ end and downstream if they are towards the 3’ end.

 

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