Question

Genetics! how can you write the sequence of a dinucleotide just by knowing the two neucleotides?

example: a dinucleotide of UTP and GMP (sugar in both is ribose with an OH on the 2' C) is 5'pppUpGoh3'. I just dont understand why?

Ex. if its GMP how would you write it in a strand? or GDP or GTP?

in the case of if its AMP how would you write it in a strand? or ADO or ATP?

if it deoxyribose?

please help

Answer 1

Okay, first of all you need to know that when any nucleotide adds to the growing chain it is in the form of a triphosphate and when it forms the phosphodiester bond with the previous nucleotide it loses its pyrophosphate ( diphosphate) and attaches to the growing chain as monophosphate.

As i have shown in this diagram.

It is very clear from your question that UTP ( uridine triphosphate ) is attached to the GMP ( Guanosine Monophosphate) in the dinucleotide. Thats why it is indicated by 3 'p' with the 'U' and single 'p' between U and G ending with a OH. As shown by the sequence 5'pppUpGoh3'

And similarly, for the trinucleotide I've drawn here the sequence would be 5'pCpUpGoh3' . At 5' there is a free phosphate group and at 3' there is a free oh group.

Remember no triphosphate or diphosphate nucleotides can attach with the growing chain. Always a nucleotide with a Monophosphate is added.( However, the 1st nucleotide can have a triphosphate as it is, which gets cleaved later on after complete synthesis of new strand )

So here it could also be 5'pppCpUpGoh3'  

For DNA ,

Deoxynucleotides are indicated simply by a suffix 'd'

For eg. For mine trinucleotide If it's a DNA ( thymine instead of uracil)

The sequence would be 5'pppdCpdTpdGoh3'

Hope you get this. :)