Final answer:
DNA does not directly encode for protein synthesis because it is transcribed into mRNA, which then travels to the ribosomes to be translated into proteins. This two-step process, transcription and translation, is the cornerstone of the Central Dogma of molecular biology.
Step-by-step explanation:
We know that DNA does not directly encode for protein synthesis because of the cellular process known as the Central Dogma. This principle involves two main steps: transcription and translation. During transcription, mRNA is synthesized from the DNA template. This mRNA then exits the nucleus and travels to the ribosomes in the cytoplasm. It is here that the process of translation occurs, where ribosomes read the mRNA sequence and assemble the corresponding amino acids to form a protein.
Evidence for this process has been well-documented since the 1960s, when scientists such as François Jacob and Jacques Monod hypothesized and identified mRNA as the intermediary molecule. The genetic code from DNA is first transcribed into complementary RNA sequences, and these sequences are later translated into the amino acid chains that create proteins. This is a systematic process where groups of three nucleotides (codons) correspond to one specific amino acid.
The enzyme reverse transcriptase is an example that further illustrates the separation of roles, as it transcribes DNA to RNA and then back to DNA without involving proteins synthesis directly. Moreover, hypotheses such as the RNA-first model suggest that ribosomal RNA may have once carried the dual function of encoding and synthesizing proteins, implying an ancient evolutionary separation of the processes.