The animation above represents the process of DNA transcription into mRNA followed by nuclear export of the mRNA transcript and translation into a protein (in this case, haemoglobin) at the ribosome. A lot of detail of course is omitted, including mRNA modification (e.g., addition of the 5′ cap and 3′ poly-A tail), splicing and editing. The animation shows transcription factors bound to the gene promoter, which recruit the RNA polymerase. The animation also shows transcription factors that are bound to an enhancer, which are brought into close proximity to the promoter by looping round of the DNA, where they can interact with the RNA polymerase and trigger the initiation of transcription.
Following transcription, the animation shows the newly synthesized mRNA transcript snaking away and exiting the nucleus through a nuclear pore into the cytoplasm. The two ribosomal subunits then lock around the mRNA and the process of translation into a protein begins, with the necessary amino acid subunits being delivered by transfer RNA molecules. Each amino acid becomes attached at its carboxyl terminus to the 3′ end of its own species of tRNA by an enzyme known as amino-acyl tRNA synthetase.
Two sites exist on a ribosome for activated tRNAs: the peptidyl site and the amino-acyl site (P site and A site respectively). The initiation codon, carrying methionine, enters the P site. The 3′ UAC 5′ anticodon of the tRNA is paired with the complementary 5′ AUG 3′ mRNA codon. The second tRNA enters the A site. An enzymatic part of the ribosome called peptidyl transferase then creates a peptide bond to link the two amino acids. Upon formation of the peptide bond, the amino-acyl bond that connected the amino acid to its corresponding tRNA is broken, and the tRNA is thus able to leave the P site. This is followed by ribosomal translocation to position a new open codon in the empty A site and also move the second tRNA — which is now bonded to a dipeptide — from the A to the P site. And so the cycle repeats until the occurrence of a stop codon that prevents further chain elongation.
I never cease to be amazed at the remarkable design and complexity of cellular information processing and retrieval.