Unit 13
Translation and the Genetic Code

Overview

In translation, the information in DNA is finally converted to a protein. Translation occurs in the cytosol of all cells. Since proteins are constantly being degraded, translation is a never-ending process.

The three forms of RNA (mRNA, tRNA, and rRNA) participate in translation. The code for the protein is found in mRNA; rRNA in ribosomes provides the protein synthesis platform; tRNA molecules bring amino acids to the ribosomes. Translation is more complex than DNA replication or RNA transcription. This complexity occurs because, while replication and transcription use the common language of nitrogenous bases, translation involves two languages: nitrogenous bases and amino acids.

The genetic code is a set of ribonucleotide bases (on mRNA) which are recognized by tRNA molecules. That is, the genetic code is the link between a sequence of bases and a sequence of amino acids. The binding of appropriate tRNA molecules to mRNA brings amino acids close enough to be combined to make proteins.

Unit 13 is divided into five lessons:

  1. The Genetic Code
  2. Transfer RNA (tRNA)
  3. Ribosomes and Protein Synthesis
  4. Control of Eukaryotic Translation and Post-translational Protein Modification
  5. The Molecular Basis of Cancer

Objectives

After completing this unit, you should be able to

  1. use the genetic code to translate mRNA sequences into (protein) amino acid sequences.
  2. explain the difference between a “codon” and an “anti-codon.”
  3. describe the role of the ribosome and tRNA in protein synthesis.
  4. explain how eukaryotic protein synthesis is controlled.
  5. outline the present biochemical knowledge of the molecular basis of cancer.
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Glossary

aminoacyl-tRNA synthetase enzyme that catalyzes the attachment of amino acids to tRNA
anti-codon set of three bases on tRNA which are complementary to the codon on mRNA
anti-sense strand the DNA strand (or portion thereof) which is not transcribed to RNA
codon set of three bases on mRNA specifying an amino acid
culture in biochemistry, the growth of cells in artificial media under controlled conditions of temperature, humidity, O2 and CO2, or some combination
elongation factors soluble proteins that assist protein synthesis
genetic code the 64 possible codons (and STOP signals) and the amino acids they specify
initiation factors soluble proteins that facilitate correct binding among mRNA, the ribosome and f Met-tRNAfMet
oncogene cancer-producing gene; the protein products of these genes are similar to normal growth factor proteins
proteolytic cleavage hydrolysis of a peptide bond under the influence of specific enzymes (called proteases)
ribosome large rRNA-protein complex in the cytosol; a ribosome binds mRNA thereby allowing protein synthesis to begin
Shine-Dalgarno sequence purine-rich set of bases on mRNA that are complementary to a set of base sequences on rRNA
wobble position third base (3′ end) in a codon; binding between the wobble position on codon and anti-codon is looser than at the other two positions
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