center Genotype and Phenotype

- mRNA -

messenger RNA
Messenger RNA (mRNA) ...
... is a single strand of RNA copied from DNA molecule. This is the molecule that carries the genetic codes.

The mRNA molecule in bacteria usually begins with the sequence CAU, copied from the initiation site on the DNA molecule. This is followed by a region of the mRNA molecule where the ribosome will eventually bind.

The information which codes for the polypeptide begins with an initiation codon or start signal that in bacteria is always the codon AUG (this codes for the amino acid n-formyl methione). The bulk of the mRNA molecule is the sequence of codons that code for the sequence of amino acids in the polypeptide chain.

At the end of the coding region are special codons that bring the message to an end. These are usually one, two or three stop codons which to not code for a specific amino acid, but simply act as message terminators.

At the very end of the mRNA molecule is double region containing a self complementary sequence that folds and base pairs into a hairpin loop. This is followed by a string of four to eight uracils. These regions play no role in the translation process, but were copied from the original DNA molecule as part of the termination of transcription (mRNA synthesis).

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Science at a Distance
© 1997, 1998, 1999, 2000 Professor John Blamire