Video Transcript: DNA and RNA - Part 2

So now let's talk about the structure of DNA and the structure of RNA. This would be RNA on one side, and this would be DNA on other. The one thing that jumps out is that RNA is a single helix. And DNA is a double helix. But if we look at the structure of both of these, which are called nucleic acids, they're mostly made up of just three parts. And so both of both of them have, let me get a color that works. Both of them have a sugar in RNA, that sugar is going to be ribose sugar. In DNA, it's going to be deoxyribose sugar, they then have a phosphate group. And then they have bases on the inside. And so if we look at this would be RNA right here. On RNA, you have a phosphate attached to a ribose sugar attached to a phosphate attached to a ribose sugar attached to a phosphate ribose sugar phosphate ribose sugar. And so the backbone, which on here would be this kind of greenish part that goes down here is simply a phosphate attached to a sugar attached to a phosphate attached to a sugar. And that's relatively boring, it's the same all the way down. Now if it's DNA, it's going to have a deoxyribose attached to a phosphate to deoxyribose. And it's going to be the same side on both sides of that backbone. What goes off the inside attached to the sugar is going to be the base or the nitrogenous base. And so in RNA, it's adenine, guanine, uracil and cytosine. So we've got cytosine, guanine, adenine and uracil. If you look at DNA, the bases that we have are cytosine, guanine, adenine and thymine. And so this is another difference between the two. In RNA, it's going to be a uracil. In DNA, it's going to be thymine. But if you look at the structure of those two chemicals, it's almost identical. And so they serve the same purpose. DNA is simply a double helix. So it's going to have bases on either side. And so if we have an A on this side, then we'll have a T on the other side.

Okay, next, I want to talk about DNA replication. When does DNA have to replicate itself? Well, every time a cell makes a copy of itself, in other words, every time you go from cell one, let's call that the zygote to two stem cells, we have to duplicate the DNA inside there. In other words, every cell in your body has the same exact DNA as that first cell. And so how does DNA copy itself? Well, Watson and Crick actually suggested since you have a double helix, and so this is the original strand of DNA on this side. Since it's double helix, what you can simply do is unzip it in the middle. If you unzip it in the middle, then we can build a new strand on this side, a new strand on this side, and now you have two strands of DNA. So we have one strand of DNA to start. And then we have two strands of DNA when we're done that one and that one. Now, the machinery of how it works is a little funky, you can only add new letters on the three prime end. And so on one side, the DNA polymerase, which is an enzyme that simply adds new bases or new nucleotides to the other side of the DNA, it'll run really smooth on this side, which is called the leading strand on the other side, it kind of has to backstitch or work in the opposite direction. But essentially, what you have is when you're done, it's unzipped. And now we have two new strands of DNA. And they're identical to that first strand. And so then that DNA is split into each of the cells as we go through the cell cycle.

Next, I want to talk about central dogma. So after they figure out the structure of DNA, mostly Francis Crick goes on. And he actually coined this term, the central dogma. He then wants to figure out how does DNA actually make us if it's the secret of life? How does it actually make us? Well, the central dogma explains how DNA makes RNA and that process is called transcription. RNA will then make proteins the proteins make the phenotypes and the phenotypes eventually make you. And so the central dogma explains how we can go from DNA to actually you. The first step is going to be called transcription. I always remember the script means to write. And so what we have is we have our DNA. So this is going to be our DNA right here.

This is going to be a gene. So it's a portion that we actually want to make a protein out of. There's an enzyme called RNA polymerase. So what RNA polymerase, just like DNA polymerase, is going to do is it's going to drive down the DNA. So RNA polymerase will drive down the DNA. And as it does that, it makes a copy behind itself. And that copy is going to be messenger RNA. So if we go again, after RNA polymerase is done, and it leaves, we now have messenger RNA. And so we started with DNA that's going to be this double strand right here. But after RNA polymerase has gone by, we now have messenger RNA or there's a message. Now the DNA right here will stay within the nucleus. And so the DNA is protected. It's like the master code inside the nucleus, it'll never leave the nucleus. But the RNA, RNA is free to leave the nucleus and actually make proteins or make things.

Okay, how does it make things? Well, that RNA is going to move out into the cytoplasm. So here's our RNA is this long stretch. And so what it'll do is it'll feed through something called the ribosomes. So this big, big green structure is going to be called the ribosome, every three letters of the RNA is going to match on three letters of a tRNA. That's what this is, it's a different type of RNA, it's called transfer RNA. And that transfer RNA is going to bring in one amino acid amino acids are the building blocks of proteins. And so what will happen is that amino acid will attach on to the string of all the other amino acids in this proteins, and then everything shifts over. So now we'll have the next one come in, and the next one come in, and the next one come in. And so what do we do here? Well, we're going from RNA, in this case, it's the messenger RNA. And what we're going to end up with right here is going to be a protein.

So let me write that more correctly, a protein is going to be what you're made up of. So when you look at my hair, or the keratin or the color of my eyes, those are all proteins. And the proteins are actually made by the ribosomes. And those are actually made in the cytoplasm. So now we've gone from the message of the DNA to the message of the RNA. And now we've translated that into a protein. So translation is moving the messenger RNA, actually into a protein. So what are the proteins create proteins eventually create phenotypes. And so phenotypes are going to be what you physically look like.

And so remember, when we talked about evolution, the peppered moth, in general will look like this, it's going to be this wide appearance. But if you add one gene to that, or one mutation, what you'll get is this appearance, in other words, just by changing the gene a little bit, we can get this huge phenotype, that phenotype change is going to be the physical characteristic that you have. And so this is how DNA and changes to the DNA will eventually create changes in the messenger RNA, which eventually create changes in the proteins, which eventually create changes in the phenotype. So the phenotype is what you physically look like.

So any kind of a change in the DNA can have changes in our physical characteristic, which then is selected for against in the environment. Now, Richard Dawkins, who writes a lot on the idea of The Selfish Gene, and how genes are actually the units of that are actually been selected for has coined this term, which I like it's called the extended phenotype.

In other words, a beaver has a number of different phenotypes. It has a bunch of number of different physical characteristics like the flattened tail, the big teeth, tiny little arms, these are all created by DNA. But what else did beavers produce? Well, they might produce a beaver dam or beaver lodge. Is that a phenotype? Is it actually made by genes? No. But it's an extension of genes. In other words, Is this allowed does this allow a beaver to survive or not? For sure it does. And so it's also going to be selected by natural selection as well. So not only the physical characteristics that you have, but that behavior that you have can be selected for as well.

Last thing I want to talk about is genetic engineering. And so going way back to the Frederick Griffith experiment, what we found is bacteria can actually share genetic information, they can share these little plasmids. And those plasmids are that auxiliary DNA can actually give them a new trait, like the ability to be very blunt in the Frederick Griffith experiment. But what scientists have figured out is since DNA is interchangeable, since we can take DNA from a human, we can cut that out, and we can insert it into a bacteria. It'll work perfectly. And so what scientists have done is they've actually inserted genes from humans into the plasmid of bacteria. And the bacteria can make copies and they can actually make proteins. And so most all of the insulin that is made today is made not by gathering it from animals or growing it in animals or using cadavers was what they used to do. They're actually having bacteria with the genes of the humans inside it to grow the insulin. And they've actually figured out now that you can actually insert the gene for insulin into safflower. And so we'll be able to grow proteins, human proteins in plants, which makes it really, really cost effective and available to all the growing number of diabetics that we have today. So that's DNA. That's RNA. And I hope that's helpful.