How is information contained in the nuclear DNA of a cell converted into proteins? Outline the role of each molecule and enzyme involved in the process.

DNA is a double-stranded nucleic acid that consists of four different bases (A, T, C, G) which make up the 'language' of the genome. Sets of three bases on the coding strand of DNA, known as a triplet codon, encode the information for one amino acid. Chains of these amino acids make up a polypeptide. The first step in the production of protein is the transcription of a DNA gene (portions of the DNA genome which code for a polypeptide) into an RNA molecule. DNA helicase binds the start of the gene and breaks the hydrogen bonds holding the two strands together, opening the DNA up to other enzymes. RNA polymerase then binds and begins to synthesise a messenger RNA molecule from the non-coding strand of DNA. Hence the codons on the RNA molecule will match those of the corresponding coding strand according to base-pairing rules. However, RNA has uracil (U) instead of thymine (T). While DNA is highly stable and lasts as a long-term genome of a cell, RNA is a short-lived intermediate which allows for control over when, and for how long, proteins are produced.

mRNA exits the nucleus and binds to a ribosome. These molecular machines produce proteins by scanning the RNA and 'reading' the codons in a process called translation. When the ribosome scans and 'reads' the START codon on the mRNA, it recruits the amino acid that the codon encodes. Different transfer RNA (tRNA) molecules bind certain amino acids and are recruited to the ribosome according to the codon that it 'reads'. This is controlled by the anti-codon sequence of the tRNA, which binds the codon according to base pairing rules. For example, a tRNA (which is bound to amino acid 1) with anti-codon UCG would bind the mRNA codon AGC. As the ribosome continues scanning the mRNA more amino acids are recruited and joined to each other with peptide bonds to form a polypeptide chain. Once the STOP codon of the mRNA has been reached, the polypeptide is complete and exits the ribosome for folding and processing. The mRNA also exits the ribosome and may now be degraded of translated again.