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The Genetic Code Genetic code: the dictionary of molecular ...
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  • 1. The Genetic Code
  • 2. Genetic code: the dictionary of molecular meaning
    • Universal: same code used by all organisms on earth
    • Triplet: 3 bases = one “word”
    • Unambiguous: each triplet has only one meaning
    • Degenerate: individual amino acids may be called for by more than one triplet (this is also referred to as redundant)
  • 3.
    • Puntuationless: no spaces between words
    • Colinear: sequence in mRNA is perfectly compatible with amino acid sequence in finished protein
    • Specific signnals
      • “ Start” = AUG
      • “ Stop” = UAA, UAG, and UGA
  • 4.
    • During transcription, one DNA strand, the template strand , provides a template for ordering the sequence of nucleotides in an RNA transcript.
      • The complementary RNA molecule is synthesized according to base-pairing rules, except that uracil is the complementary base to adenine.
    • During translation, blocks of three nucleotides, codons , are decoded into a sequence of amino acids.
    Fig. 17.3
  • 5.
    • By the mid-1960s the entire code was deciphered.
      • 61 of 64 triplets code for amino acids.
      • The codon AUG not only codes for the amino acid methionine but also indicates the start of translation.
      • Three codons do not indicate amino acids but signal the termination of translation.
    Fig. 17.4
  • 6.
    • To extract the message from the genetic code requires specifying the correct starting point.
      • This establishes the reading frame and subsequent codons are read in groups of three nucleotides.
      • The cell’s protein-synthesizing machinery reads the message as a series of nonoverlapping three-letter words.
  • 7. What Does DNA Say?
    • Coding strand: provides info for the template strand
    • Template strand: provides the template for mRNA
    • Template strand is read 3’ ->5’
    • mRNA is made 5’->3’
    • Amino acids are coded for on the mRNA!!
  • 8. Steps
    • Write template DNA strand from coding strand (it is complementary)
    • mRNA is complementary to template DNA strand (remember U intead of T)
    • tRNA strand is complementary to mRNA
    • Use mRNA to get amino acids
    • Start means start and stop means stop