animal cell membrane diagram (graphic)

Protein Synthesis Diagram: simplified picture of a cell with mRNA, tRNA and ribosomes working to produce protein.. This image is 500 pixels across the original is 3,346 pixels across.

Above is a simplified diagram showing how proteins are manufactured in a cell. At bottom right, messenger RNA (mRNA) is being produced in the nucleus. mRNA molecules are shown as yellow string like molecules. This process, which copies the information stored in the nuclear DNA into complementary code in the mRNA, is called transcription. The mRNA then leaves the nucleus via a nuclear pore (nuclear pores are the flower shaped structures embedded in the nuclear membrane) and moves into the cytoplasm. Ribosomes attach to the mRNA and start to translate the information contained in the mRNA into a sequence of amino acids.

Ribosomes are small (about 24nm diameter) molecular scale machines that crunch along the mRNA, reading it like a tape, and adding appropriate amino acids together to create proteins. The specific amino acids (shown as purple blobs) are recognised, captured and brought to the ribosomes by transfer RNAs (tRNAs). tRNA molecules are shown as the orange twisted rope like molecules. Inside a ribosome, the newly arrived tRNA, bearing its specific amino acid, docks next to the tRNA molecule already inside the ribosome. The polypeptide chain is then attached to the newly delivered amino acid and so comes to hang from the incoming tRNA. The first (now liberated) tRNA then exits from the ribosome. The ribosome grinds along the mRNA and a space is created to accommodate a new incoming tRNA with its attached amino acid. This process is repeated each time an amino acid is added.

This diagram is very simplified but gives the essence of the process of protein manufacture in the cell and should be very useful for illustrating articles on proteomics or as an introduction to protein synthesis. Proteomics essentially means the identification and understanding of proteins (in a cell or organism) and is comparable to the term genomics which applies to the genes (DNA). There is considerable interest in proteomics since it follows naturally from genomics (the chracterisation of the genome) and is the domain where much drug development may occur.

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