Molecular Evolution and Information

Each Codon Specifies an Amino Acid

Each codon in a gene specifies a particular amino acid. Therefore, a gene determines the chemical properties of a specific protein by specifying its amino acid sequence. A simplified example is shown in figure 3.8. Four DNA codons and the amino acids that they specify are depicted in this picture. During transcription of the hypothetical DNA sequence, the DNA is written into a corresponding messenger RNA (mRNA). During translation, mRNA is translated using the genetic code to create a new protein. The code assigns an amino acid to each codon.
    The properties of amino acids are determined by their side chains. In figure 3.8, these side chains branch from the main protein chain. The side chains of amino acids give them unique chemical properties. 1) Some side chains are chemically reactive. These side chains are used by proteins to interact with other chemicals. 2) Other side chains do not like to dissolve in water. Such side chains are called hydrophobic. Hydrophobic side chains cause proteins to fold up into complex three dimensional shapes.

Figure 3.8: Translation





    To verify understanding, all readers should make sure that they can use table 3.2 to follow how the hypothetical DNA sequence in figure 3.8 is transcribed into the resulting RNA sequence, and how the resulting RNA sequence is translated into the final amino acid chain.


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