DNA Structure, Replication, and Genetic Code Translation

DNA, Genetic Code, and Translation

Classical genetics is devoted to studying the mechanisms of heredity. In the 1930s, questions were raised, and geneticists began to explore the nature of the gene. Even earlier, there were no doubts about the existence of genes.

The Discovery of DNA Structure

The first chemical analysis of genetic material showed that the eukaryotic chromosome consists of deoxyribonucleic acid (DNA) and proteins. Both DNA and proteins were good candidates for the molecule that carries the genetic material.

In 1953, James Watson and Francis Crick gathered data from different studies on DNA. They postulated a model for DNA structure and were able to deduce that DNA is a double helix, an intertwined and long structure. An essential property of the genetic material is its ability to make exact copies of itself.

DNA Replication: The Semiconservative Process

Watson and Crick assumed there must be some way that DNA molecules could replicate quickly. They proposed a mechanism for DNA replication and deduced that the DNA molecule is replicated by a semiconservative process, meaning half of the original molecule is preserved. The model proposed by Watson and Crick showed how information could be stored in the DNA molecule.

The Role of Proteins and RNA

In the 1940s, biologists began noticing that all the biochemical activities of living cells depend on certain different and specific proteins. It was becoming clear that the specificity of different enzymes is the result of the primary structure of these proteins.

The DNA molecule contains coded instructions for biological structures and functions. Furthermore, these instructions are carried out by proteins. Ribonucleic acid (RNA) was a good candidate to play a role in the translation of this information.

Types of RNA

There are three main kinds of RNA:

• Messenger RNA (mRNA): Carries the genetic message from DNA.
• Transfer RNA (tRNA): Helps translate the mRNA message into protein.
• Ribosomal RNA (rRNA): A component of ribosomes, the protein synthesis machinery.

Translation and the Universal Code

Once the genetic code was known, attention focused on the problem of how the information encoded in DNA and transcribed into mRNA is then translated into the specific sequence of amino acids in proteins.

Hugo de Vries defined mutation in terms of features that appear in the phenotype. More precisely, a mutation is a change in the nucleotide sequence in the DNA. The genetic code is the same for virtually all life; it is universal.