The genetic code
Overview: Gene expression and the genetic code
- In transcription, the DNA sequence of a gene is "rewritten" using RNA nucleotides. In eukaryotes, the RNA must go through additional processing steps to become a messenger RNA, or mRNA.
- In translation, the sequence of nucleotides in the mRNA is "translated" into a sequence of amino acids in a polypeptide (protein or protein subunit).
Code crackers: How the genetic code was discovered
The triplet hypothesis
Nirenberg, Khorana, and the identification of codons
- A way to make artificial mRNA molecules with specific, known sequences.
- A system to translate mRNAs into polypeptides outside of a cell (a "cell-free" system). Nirenberg's system consisted of cytoplasm from burst E. coli cells, which contains all of the materials needed for translation.