DNA transcription

[student12]

My question is in regards to DNA transcription. Please read below:

The RNA polymerase recognises the promoter region of a gene and initiates transcription, adding nucleotides into the growing RNA molecule. This molecule is then called a primary transcript. It is modified into a mRNA by enzymes that cut out the intron regions and join the exon regions together.
My text book then states that....without any further explanation.
"The mRNA molecule is complete when its two ends are modified. It is chemically capped at the 5' end and a tail of As (a poly-A-tail is added at the 3' end."

Can someone please explain the Bold type section above? because I've just started this section in school...[/b]

[oppox]

Well in the book I have says that it hasnt been clearly established why the poly A tail is added. However some studies have shown that it stabilizes the RNA and its a more effective template for protein synthesis compared to RNA without the tail.

[LilKim]

There are three important steps in the production of mature mRNA (that is capable of being exported from the nucleus and translated by ribosomes).

.... 5' Cap is added during mRNA transcription by guanyltransferase (it add's an "upside-down" Guanine to the 5-end of mRNA) ... the introns are then spliced out .. and then polyadenylase adds a poly A tail (necessary for export and message stability.

check out : http://en.wikipedia.org/wiki/MRNA#mRNA_structure

good luck!
- KIM