mRNA

• the rRNA could determine which AA is which by its tRNA "tag,"
• but the ribosome needs to know which AA it ought to be looking for.
• The simplest way to provide this message:
  • convert the AA sequence of the desired protein to a list of tRNA codes
  • deliver this list as a single large molecule of RNA, called messenger RNA [or mRNA].

• Due to nucleotide pairing 'rules' the mRNA must list the opposite of what it means.
  • the tRNA, AGC which codes for Ser,
    would be listed on the mRNA as UCG.

• given the 'protein' from before:
  • Met-Gly-Ser-Glu-Val-STOP
• and the attached tRNA molecules:
  • Met-UAC
  • Gly-CCA, Gly-CCG, Gly-CCU, or Gly-CCC
  • Ser-AGA, Ser-AGG, Ser-AGU, Ser-AGC, Ser-UCA, or UCG
  • Glu-CUU, or Glu-CUC
  • Val-CAA, Val-CAG, Val-CAU, or Val-CAC
  • STOP = AUU, AUC, or ACU
• one possible mRNA to describe the tRNA sequence, therefore AA sequence:
  • AUG,GGC,UCG,GAG,GUC,UAA
  • or without the commas
  • AUGGGCUCGGAGGUCUAA

DNA

• Complete set of instructions for all protein synthesis required by an organism
• stored in Nucleus as even larger molecules, listing all required mRNA molecules
• substituting deoxyribose, we have DNA
• applying nucleotide pairing rules, again we produce the opposite:
  recall DNA substitutes Thymidine [T] for Uracil [U]

• given the mRNA from earlier:
  • AUGGGCUCGGAGGUCUAA
• the coding DNA would be:
  • TACCCGAGCCTCCAGATT

Genetics:
DNA to Protein

• to summarize:

• copying of information from DNA to mRNA is transcription
• using information from mRNA for Protein synthesis is translation

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© 2004-2005 TwoOldGuys ™

revised 19 aug 2006