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Biology: Transfer RNA Role: Charging tRNA Molecule


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  • Type: Video Tutorial
  • Length: 9:26
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 101 MB
  • Posted: 07/01/2009

This lesson is part of the following series:

Biology Course (390 lessons, $198.00)
Biology: Genetics: DNA & Replication (35 lessons, $54.45)
Biology: Translation (5 lessons, $8.91)

Taught by Professor George Wolfe, this lesson was selected from a broader, comprehensive course, Biology. This course and others are available from Thinkwell, Inc. The full course can be found at The full course covers evolution, ecology, inorganic and organic chemistry, cell biology, respiration, molecular genetics, photosynthesis, biotechnology, cell reproduction, Mendelian genetics and mutation, population genetics and mutation, animal systems and homeostasis, evolution of life on earth, and plant systems and homeostasis.

George Wolfe brings 30+ years of teaching and curriculum writing experience to Thinkwell Biology. His teaching career started in Zaire, Africa where he taught Biology, Chemistry, Political Economics, and Physical Education in the Peace Corps. Since then, he's taught in the Western NY region, spending the last 20 years in the Rochester City School District where he is the Director of the Loudoun Academy of Science. Besides his teaching career, Mr. Wolfe has also been an Emmy-winning television host, fielding live questions for the PBS/WXXI production of Homework Hotline as well as writing and performing in "Football Physics" segments for the Buffalo Bills and the Discover Channel. His contributions to education have been extensive, serving on multiple advisory boards including the Cornell Institute of Physics Teachers, the Cornell Institute of Biology Teachers and the Harvard-Smithsonian Center for Astrophysics SportSmarts curriculum project. He has authored several publications including "The Nasonia Project", a lab series built around the genetics and behaviors of a parasitic wasp. He has received numerous awards throughout his teaching career including the NSTA Presidential Excellence Award, The National Association of Biology Teachers Outstanding Biology Teacher Award for New York State, The Shell Award for Outstanding Science Educator, and was recently inducted in the National Teaching Hall of Fame.

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I don't want to give you an impression that this stuff is simple now. When I say to you, "Oh, tRNA brings an amino acid," well, it does. But you know, everything works together and there's something you need to learn about tRNA and how it gets that amino acid to begin with. Yes, that amino acid is going to be very specific to the anticodon loop and the anticodon loop is at the bottom. Let's take another quick look at tRNA and make sure we're all there. Here's tRNA, at least in its hypothetical form. We'll show you the real form of tRNA in a second. But with its 3' end where the amino acid's going to go and its anticodon loop down here. And there's going to be a correspondence between what's here and what's up here. But you know, the reality is that tRNA doesn't look like that. tRNA, in its true three-dimensional structure, looks something like this. It ends up kind of this L-shaped structure. And down here is the anticodon loop and up here is the amino acid attachment site. And you can see the fact that it formed this three-dimensional structure with hydrogen bonds. But that's tRNA.
The problem is, that's hard to draw, and so is that other thing. You've seen the way I draw. Sometimes, for diagrammatic sake, we could draw it something like this, like this giant firecracker with prongs on the bottom of it, and that works for me. Here's my anticodon. There's my amino acid attachment site. My students used to tell me I draw like kind of a ghost - with its loops and I put my anticodon down there and put my amino acid there. It's doesn't matter how you draw it. What matters is, get the concept of what it's going to do. That's the key.
And what I want to talk to you right now, very briefly, is how does it get this amino acid? How does it get a specific amino acid that in only going to correspond to this anticodon? And you know what? Lightbulbs should be flashing in your head - I just used the word "specific." And you guys know biochemistry. You are the biochemistry kings and queens. You know biochemistry. And as soon as I say the word "specific," what word do you think of? Right, enzymes - you're thinking enzymes. And you're absolutely right. There must be enzymes involved with this. This sounds an awful lot like enzymes, and indeed friends, it is enzymes. Enzymes come in and, in fact, twenty different enzymes come in. Think about it, why twenty different enzymes? Twenty different amino acids - therefore, we must charge different tRNAs differently. And therefore, in order to charge - in other words, get these RNAs with their amino acid - we must give them - put them - into different enzymes. And the name of the enzyme, generically, is called aminoacyl-tRNA transferase. And folks, I got to tell you if I haven't stressed phosphorylated intermediates enough yet, here they come again. Phosphorylated intermediates - the compounds you form to magically - and it's not so magic anymore. You're biochemists, for goodness sakes. You get it. Those phosphorylated intermediates are going to take that energy in those high-energy bonds in the tri-phosphates. And when the energy is released, it's going to be used to run endergonic reactions. That's energy that's released is going to be used to make a synthesis of some kind. Remember, endergonic reactions don't happen spontaneously. tRNA- you know this guy is not, on its own, going to pick up an amino acid just because it's a nice molecule, or just because it has AAG here. This is a synthetic. This is endergonic. You need to form phosphorylated intermediates to make this happen, and therefore, we need to bring in ATP - adenosine triphosphate that's going to run the show. If you get that, it's going to be nice and simple and fun and diachromatic and black and white. You get it? Good. Let's take a look at it.
All we have to do to get the concept is follow the diagram. Let's see if it makes sense. Forest, trees, story - what do want to do? We want to take a tRNA and we want to give it an amino acid. Remember that? So in order to do that, we have to somehow get energy involved. Here's my aminoacyl-tRNA synthetase. So this particular enzyme is going to grab, in its active site, some things. What's it going to grab? Number one, it's going to take a specific amino acid. And so it's going to take that amino acid and put it into its active site. And remember what enzymes do. In their active sites, in an endergonic reaction like this - in other words, in an anabolic situation, where you're putting stuff together - it's going to bring two parts of the substrate together, whether it's two monosaccharides to make a disaccharide, or in this case, an ATP molecule and an amino acid of choice. And this particular amino acid - it doesn't matter, it's one of the twenty - in it comes. And now we form this ATP amino acid enzyme complex.
The first thing that happens, when that occurs, is that two of those phosphate groups break off. And so what you're going to do - and I'll come back to this - is you are now going to take - okay, if this is my enzyme and here's my amino acid, the first thing that's going to happen is that amino acid is going to pick up one of those phosphate groups, like so, and release a pyrophosphate. Do you remember what a pyrophosphate is? Okay, it's going to release two phosphate groups, which are eventually going to end up as two inorganic phosphates just kind of freely floating around the cell. So, in other words, it's picking up this phosphate group, and that phosphate group is still going to be attached to adenosine. So this is an AMP - Adenosine monophosphate amino acid complex on the enzyme.
Step one - summary - in comes an amino acid, in comes ATP. ATP is dephosphorylated and two phosphates jump off. Now, the AMP left behind bonds to the amino acid. You now have an amino acid with a high-energy bond on it, attached to an adenosine. What do you think is going to happen next? Yes, what's going to happen next is along is going to come my tRNA. So back to my diagram - here we are. We've lost our pyrophosphate. We now have the amino acid with AMP attached to it. And now my tRNA - my specific tRNA for this particular amino acid - can come in here and look what's going to happen. There's an energy release here. So once again, we're passing energy along those steppingstones. But that high-energy bond is going to be transferred. So here comes tRNA - it's coming in. And what's going to happen is the AMP is going to pop off. The AMP pops off. There it is. And what happens is the energy is going to be transferred to a bond between the tRNA and the amino acid.
So now, you're going to have the following substance. Your enzyme - just like enzymes always do - will be recycled. Your AMP is released. But what's most important is this. What's most important is you now have an amino acid/tRNA complex with that high-energy bond, thanks to phosphorylated intermediates. Now I have a question for you. What are going to do with this? You should know enough to answer this. What are going to do with this? This is going to transfer - it's called transfer RNA - it's going to transfer that amino acid and somehow getting them to the messenger RNA. And that's what we're going to see next.
Molecular Genetics
The Role of Transfer RNA: Charging a tRNA Molecule Page [1 of 2]

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