The Origins of Research on the Genetic Code (AQA A Level Biology) : Revision Note

Appreciating How the Function of DNA Was Determined

• DNA was actually first observed in the 1800s by a Swiss scientist called Friedrich Miescher

  • Miescher is credited with being the first person to discover DNA (although he named it ‘nuclein’) and define it as a distinct molecule in 1869

• However, many scientific researchers at that time doubted that this newly discovered DNA molecule could carry the genetic code

  • They doubted this because of the relatively simple chemical composition of DNA (because DNA was only made up of simple repeating nucleotides, which themselves were only composed of three parts: a phosphate group, deoxyribose, a nitrogen-containing organic base

  • For example, some scientists hypothesised that genetic information must be carried by proteins, which show much higher levels of chemical complexity

  • For example, proteins are which are made up of 20 different amino acids whereas DNA is made up of only 4 different nucleotides

• As a result, it wasn’t until the 1940s that the role of DNA in genetic inheritance began to be more fully researched and understood

• By 1953, experiments had confirmed that DNA carried the genetic code

  • It was understood that, despite there being only 4 nucleotides, the use of the triplet code enabled much variation (the code is universal and degenerate)

  • The location of DNA, protected in the nucleus, enabled the security of the genetic material rather than proteins that are found in the cytoplasm and susceptible to hydrolysis

  • DNA is easily copied and therefore conserved throughout generations of cells and inherited between generations within families

• 1953 was also the year in which Watson and Crick confirmed the double-helix structure of DNA using Rosalind Franklin’s X-ray data