Hi i am a new member here and i'm sorry for this paticular amateurish question but its been confusing me in my biology class.

My question is why uracil is used to replace thymine in messenger RNA manufacture, while during DNA replication thymine is used? They both are formed from free-floating nucleotides within the nucleus so this has just kind of confused me. Also if this is answered in another post (i have to admit i havn't look too hard) please can i have a link.

Thank you in advance.

Different Polymerases, GTFs, etc. etc. look it up in wikipedia

The answer has to do with hydrogen bonding potential. The thymine has the extra methyl group and uracil has H in place (everything else stays the same). The methyl group on thymine will create more surface tension in water which implies that the hydrogen bonding potential of the DNA is masw higher than RNA.

 

The lower surface tension and hydrogen bonding potential of RNA is beneficial to protein translation, since most proteins contain residual hydrogen bonding potential, and as they grow in size that number increases. The lower H-bonding potential of the RNA allows larger proteins to form than if mDNA was used.

The second half of the uracil and thymine question is connected to cell cycles and the production of DNA. As the cell advances toward the replication of the DNA, the accummulation of proteins needed to define two daughter cells with increase the aqueous hydrogen bonding potential within the cytoplasm. This will shift equilibirum monomer production away from the lower hydrogen bonding potential RNA monomers, containing the lower surface tension uracil, into the higher surface tension thymine and hydrogen potential potential DNA monomers. This new flux into the nuclear membrane will increase the hydrogen bonding potential within the nuclear membrane volume causing a new equilbirium for the DNA, which leads to the equilibrium production of the higher hydrogen bonding potential duplicated DNA.