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The innermost workings of how a simple code is turned into flesh and blood. This is what Francis Crick called the central dogma of modern biology: how DNA makes protein. It starts with a bundle of factors assembling at the start of the gene. It’s these that trigger the first phase of the process: reading off the information that will be needed to make the protein. The gene is the length of DNA stretching away to the left. Everything’s ready to roll. 3...2...1… The blue molecule racing along the DNA is reading the gene. It’s unzipping the double helix and copying one of the two strands. The yellow chain snaking out of the top is a copy of the genetic message... ...and it’s made of 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 make an exact copy... ...of the As, Cs, Gs and Ts of the gene. The only difference is that in the RNA copy, the letter T is replaced with the closely related nucleic acid known as U. You are watching this process, called transcription, in real time. It’s happening right now, in almost every cell in your body. When the RNA copy is complete, it snakes away from the nucleus... ...and into the outer part of the cell. Then, in a dazzling display of choreography, all the components of another molecular machine lock together around the RNA... form a miniature factory called a ribosome. 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. The amino acids are the small red tips attached to the transfer molecules. There are different transfer molecules for each of the 20 amino acids. They all carry a specific three-letter code that will be read by the machine. Now we come to the heart of the process. Inside the ribosome, the RNA is pulled through like a tape. The code for each amino acid is read off, three letters at a time, and matched to three corresponding letters on the transfer molecule. When the right transfer molecule plugs in, the amino acid it carries is added to the growing protein chain. Again, you are watching this in real time. And after a few seconds, the assembled protein starts to emerge from the ribosome. Ribosomes can make any kind of protein. It just depends what genetic message you feed in on the RNA. In this case, the end product is hemoglobin. The cells in our bone marrow turn out a hundred trillion molecules of it per second.

Video Details

Duration: 4 minutes and 6 seconds
Country: United States
Language: English
Producer: PBS
Director: PBS
Views: 4,660
Posted by: locumele on Sep 21, 2009

From the PBS production called "DNA: The Secret of Life". A Windfall Films Production for Thirteen/WNET New York in association with Channel Four.
© 2003 Educational Broadcasting Corporation.

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