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Mr. Andersen explains the Central Dogma of biology. He shows how DNA is transcribed to form mRNA and how mRNA is translated into a protein.
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Transcript Provided by YouTube:
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Hi. This is Mr. Andersen. And I get a lot of e-mails from students around
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the country and they want me to give them a shout out. And so I’m going to give them
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shout outs now at the bottom of this video. But the student’s in my 3rd period AP Biology
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class complained a little bit about that, and they wanted to know why I didn’t give
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a shout outs to them. So what I thought I would do is give them a video shout out. So
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if you would, period 3 let’s see it. Okay. This is Mr. Andersen. And today I’m going
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to be drawing out the central dogma. Since it’s hard for me to actually look at the camera
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and draw, I’m going to shrink my head and get that out of the way. Now first of all,
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what is the central dogma? The central dogma is a term that was coined by Francis Crick.
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And so after they discovered the structure of DNA and the DNA if we draw out what it
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looks like, DNA looks like this. It’s a double helix. And so this would be a helix on one
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side. And another helix that kind of wraps around that. And looks like this. So once
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they figured out the structure of DNA the next job was to figure out, okay, well how
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do we actually take DNA and then make something out of it. And so how do we go from DNA to,
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this, let’s us red for RNA, to messenger RNA. And then how do we go from messenger RNA eventually
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to, let me put you way down here. So how do we actually go to you? So how do we get from
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DNA to messenger RNA and eventually to you. So what I’m going to try and sketch out is
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how that process actually works. And so let’s first of all start on the left side with DNA
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to messenger RNA. So first of all what does messenger RNA look like? Messenger RNA looks
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like this. If we were to sketch out what it looks like it’s linear. So it’s just one line.
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On one side we have what’s called the 5 prime cap. And that’s kind of like a head on this
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side that identifies this as messenger RNA. On the other side we have what’s called a
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poly A tail. So that’s a bunch of adenines in a row. And so what that cap and the tail
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do is they actually protect the messenger RNA. And so how do we go from DNA to RNA?
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There is a protein called RNA polymerase. And what it’ll do is it’ll cruise down one
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side of the DNA and it will read off the letters and then put them into messenger RNA. And
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so in my sketch here, to keep track of everything, what I’m going to do is I’m going to draw
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a line all the way across. And on top of that line, this is going to be inside the nucleus.
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And then on the bottom of this is going to be in the cytoplasm. And so the first thing,
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anything above this is going to take place in the nucleus. And so let’s go back to a
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color that is DNA. So DNA, if we get even more specific into what DNA looks like, it’s
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going to have a backbone that looks kind of like this. It’s going to have a side to it.
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And so this is going to be what’s called the 3 prime end. And then on the other side we
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have what’s called the 5 prime end. And then they have letters on the inside. And those
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letters are what are called nucleotides. And so let’s sketch out what those letters might
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look like. So this would be one. This would be another letter. And then let me put some
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letters that go with this. So this would be the letter A. This stands for adenine. This
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would be cytosine. This would be another cytosine. This would be another adenine. This would
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be a guanine. And then this on this side would be a thymine. So there are 4 different types
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of letters but they’re organized in specific ways. And so you’ll notice on here that some
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of these actually protrude a little more into the middle. Adenine is actually a purine.
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So that means it’s a double ring structure. So it scoots out a little bit more. And it
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will always match with thymine. So you can almost imagine in your head the other side
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of the DNA and how the thymine would hydrogen bond perfectly to the adenine and guanine.
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And it’s going to fit perfectly with the cytosine. And so if we were copying DNA, the DNA simply
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splits in the middle and the DNA polymerase is going to add the complimentary side. But
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that’s not what we’re doing. What we’re trying to do is show how we can go to RNA from that.
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So let me draw the RNA. So RNA is going to look like this. It also has a backbone but
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it’s just linear. And so opposing the adenine we’re going to have a uracil. And opposing
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the cytosine we’re going to have a guanine. Opposing the other cytosine we’re going to
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have another guanine. On the other side of the adenine we’re going to have a uracil.
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On the other side of the guanine we’ll have a cytosine. And on the other side of the thymine
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we’re going to have an adenine. And so the information that was up here is now information
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that is in the messenger RNA. And that can eventually leave the nucleus and enter into
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the cytoplasm. And so what does that actually look like? Let me choose another color. If
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we were to go out here into the cytoplasm, so on the big scale, if something totally
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microscopic can be the big scale, we’ve got our messenger RNA that looks like that. Let
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me try and do that in the right color. It’s going to have a cap on it. It’s going to have
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a poly A tail on that side. So this will actually scoot out through the pours in the nucleus.
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And the first thing that’s going to grab ahold is going to be the bottom of a ribosome. We’ve
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then attach a transfer RNA. And the first thing that will attach to that is always a
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thymine. And then we have other transfer RNAs that will just keep coming in. And each of
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those are going to bring a different amino acid. And so eventually what you get is a
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string of amino acids. And each of those amino acids will eventually become part of a protein.
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So the other part I’m missing on here is the ribosome. So this would be the ribosome here.
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This would be the messenger RNA. And then these are going to be the transfer RNAs that
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pull each of their amino acids to the middle. And so this is how it takes place in the cytoplasm.
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If we were to go over here and use kind of our code again, amino acids will say are black.
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Amino acids are going to look like this. So this would be one amino acid. These three
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letters in messenger RNA are what are called a codon. And those are going to code for a
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specific amino acid. In this case UGG, and you’d have to use a chart to figure this out,
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is going to code for tryptophan. And the next three letters, UCA are going to code for a
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different amino acid. And in this case that’s going to code for serine. And so the process
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by which we go from DNA to messenger RNA, that process is called transcription. What
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we’re really doing is we are scripting or we are writing out the message in the DNA
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in messenger RNA. This next process is called translation. Translation is when we take the
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messenger RNA and actually make a protein out of it. Now is this a protein right here?
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No. This is simply a polypeptide. It’s a bunch of amino acids attached together. That protein
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will eventually fold into a specific shape with alpha helixes and beta pleated sheets.
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And it will have a three dimensional shape that gives it a specific structure. And so
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if we were to draw out what a human looks like. Let me try to do my best at this. And
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let’s give this guy some glasses. And maybe we’ll give him a chin. and a nose. And a mouth
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like that. So when he have a guy like this, who has for example red hair, the color of
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that red hair is a protein. And the protein was created by the DNA making messenger RNA
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and eventually making a protein. In this case it’s for red hair. Or maybe it’s for freckles.
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Or maybe it’s for blue eyes. And each of those is a protein. And that protein’s message was
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in the messenger RNA. Before that it was in the DNA. And so this whole process is called
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the central dogma. It’s how we go from a message in the DNA to a message in the messenger RNA.
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And eventually we go to you. And so I hope that’s helpful.
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This post was previously published on YouTube.
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Photo credit: Screenshot from video