1.5.4 The Origins of Research on the Genetic Code

Key Milestones in Genetic Code Research:

1. Discovery of DNA as Genetic Material:

• In the 1940s, experiments by Avery, MacLeod, and McCarty provided the first evidence that DNA, not protein, was the molecule responsible for heredity.

2. Structure of DNA:

• In 1953, James Watson and Francis Crick, with the help of Rosalind Franklin's X-ray diffraction images, discovered the double helix structure of DNA.
• This structure suggested a mechanism for replication and hinted that DNA carried genetic information in the sequence of its bases.

3. Deciphering the Genetic Code:

• In the 1960s, scientists began to unravel how sequences of DNA bases encode for amino acids in proteins.
• Marshall Nirenberg and Har Gobind Khorana were instrumental in cracking the genetic code, showing that sets of three bases (known as codons) correspond to specific amino acids.
• This led to the understanding that the genetic code is universal, redundant (multiple codons for some amino acids), and unambiguous (each codon specifies only one amino acid).

4. Understanding Codons:

• A codon is a sequence of three nucleotides in mRNA that corresponds to a specific amino acid or a stop signal during protein synthesis.
• There are 64 codons in total, of which 61 code for amino acids and 3 serve as stop codons.

Importance of Genetic Code Research:

• Understanding Protein Synthesis: This research provided a framework for understanding how DNA sequences are translated into proteins, the workhorses of cells.
• Advances in Genetics and Medicine: Knowledge of the genetic code has paved the way for advancements in genetic engineering, biotechnology, and personalised medicine.

Research on the genetic code has been foundational in molecular biology, revealing how genetic information is used to build and regulate the functions of all living organisms.