Molecular Genetics

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• In the flow of information from genotype to phenotype, two steps require the copying of nucleotide sequence information into a different form.
  • 
    The first step, the copying of the DNA information into RNA, is designated transcription by analogy with medieval monks sitting in their cells copying, letter by letter, old Latin manuscripts. The letters and words in the new version are the same as in the old, but they are written with a different hand and thus have a slightly different appearance.
  • 
    The second step, in which amino acids are polymerized in response to the RNA information, is called translation. Here, monks (a few centuries later) take the Latin words and find English, German or French equivalents. The product is in a different language, in our case in the language of protein sequence.
  • After transcription and before translation the RNA transcripts are processed to produce mature messenger RNA (mRNA).
  • The products of translation, polypeptides, are also processed, producing the mature proteins.

Each of the steps and the RNA and protein processing reactions rely on signal elements within the informational molecule to signal the correct copying or processing.

• Mature proteins contribute to phenotype in many ways:
  • structural (membranes, fibers)
  • catalytic (synthesizing other structural macromolecules, lipids, polysaccharides, etc.; producing energy for these syntheses and for maintenance of the cell)
  • regulatory (turning on and off various reaction paths) in response to environment or developmental plan.

This is page 2 of Molecular Genetics by Ulrich Melcher, © 1997, 1998, 2001