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AP. Biology essay
The finding of the Introns and the exons was one of the most significant
discoveries in genetics in the past fifteen years. split genes were discovered
when lack of relation between DNA sequences were seen during. DNA- mRNA
hybridation. For all new mRNA, they must be transcribed by RNA polymerase
enzymes. The transcription begins at the promoter sequence on the DNA and works
down, thus the nucleotide sequence of the mRNA is complimentary to the one of
DNA. In eukaryotes the mRNA is processed in the nucleus before transport to the
cytoplasm for translation. In order for the mRNA to become true functioning
RNA it must under go several stages of modification.
At first, when the mRNA is produced, a cap is added enzymaticully to the
5' end of the RNA by linking a 7-methylguanosine residue by a triphosphate bond
this is called the G-cap. The G-cap is necessary for translation. The subunit
of the ribosome recognizes the G-cap and then finds the initiation codon to
start translation. As the mRNA comes finishes transcription, the Poly A tail is
added to the 3' end. As the two ends are placed the mRNA becomes pre-mRNA.
The pre-mRNA consists of splicing and non-coding regions. pre-mRNA
molecules are much longer than the mRNA molecule needed to code for its protein.
The regions that do not code for amino acids; aa, are scattered all along the
coding region. The genes are split with coding regions, called exons, short for
expressed regions; in between the exons the non-coding region called introns
exist. Before the translation of mRNA the introns must be spliced off.
Splicing is an complicated process for the cell. It must locate every intron in
the primary transcript. An average mRNA consists of eight ...
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