The Central Dogma of Biology
A 3D animation shows how the DNA genetic "code" leads to proteins that help us develop and function. Originally created for Learn About Spinal Muscular Atrophy ( http://www.learnaboutsma.org/ ) TRANSCRIPT: The DNA double helix contains two linear sequences of the letters A C G and T, which carry coded instructions. Transcription of DNA begins with a bundle of factors assembling at the start of a gene, to read off the information that will be needed to make a protein. The blue molecule is unzipping the double helix and copying one of the two strands. The yellow chain snaking out of the top is a close chemical cousin of DNA called RNA. The building blocks to make the RNA enter through an intake hole. They are matched to the DNA - letter by letter - to copy the gene. At this point the RNA needs to be edited before it can be translated into a protein. This editing process is called splicing, which involves removing the green non-coding regions called "introns", leaving only the yellow, protein-coding "exons." Splicing begins with assembly of factors at the intron/exon borders, which act as beacons to guide small proteins to form a splicing machine, called the spliceosome. The animation is showing this happening in real time. The spliceosome then brings the exons on either side of the intron very close together, ready to be cut. One end of the intron is cut and folded back on itself to join and form a loop. The spliceosome then cuts the RNA to release the loop and join the two exons together. The edited RNA and intron are released, and the spliceosome disassembles. This process is repeated for every intron in the RNA. Numerous spliceosomes remove all the introns so that the edited RNA contains only exons, which are the complete instructions for the protein. Again, this is happening in real time. When the RNA copy is complete, it snakes out into the outer part of the cell. Then all the components of a molecular factory called a ribosome lock together around the RNA. It translates the genetic information in the RNA into a string of amino acids that will become a protein. Special transfer molecules — the green triangles — bring each amino acid to the ribosome. Inside the ribosome, the RNA is pulled through like a tape. There are different transfer molecules for each of the twenty amino acids, shown as small red tips. The code for each amino acid is read off the RNA, three letters at a time, and matched to three corresponding letters on the transfer molecules. The amino acid is added to the growing protein chain and after a few seconds the protein starts to emerge from the ribosome. Ribosomes can make many proteins. It just depends what genetic message you feed into the RNA.