Describe how a cell produces a mature protein from DNA, including the main enzymes involved and where each stage takes place.

Initially, the double helix structure of DNA is broken down by DNA helicase in the region of the gene encoding the protein. Then the template strand of the gene is transcribed into RNA by RNA polymerase. After this stage the RNA is modified, intron regions of the gene are removed by spliceosomes and a 5' cap and 3' poly-A tail are added. This produces messenger RNA (mRNA) through the action of RNA polymerase. These processes occur in the nucleus. The mRNA is then transported out of the nucleus and to the ribosomes. The ribosomes recognise the 5’ cap of the mRNA and bind to it. At this stage specific tRNAs carrying amino acids are recruited to the ribosome. Each tRNA corresponds to a specific sequence of three base known as a codon. These codons correspond to an amino acid. The first tRNA binds to the start codon (initiation), then subsequent tRNA corresponding to the next codon binds and the amino acid from the previous codon is transferred across to the new tRNA by peptidyl transferase. This process is repeated for the entire length of the coding region of the mRNA (elongation); once it reaches the stop codon the process ends (termination). This process is known as translation and occurs in the cytoplasm or surface of the endoplasmic reticulum but is facilitated by the action of ribosomes. After translation, the amino acid chain is folded into its protein structure. At this point post-translational modifications may take place to produce the final functional protein.