Transcription and Translation

Hi. It's Mr. Andersen and in this podcast I'm going to talk about transcription and translation. And in biology that's how we go from DNA to RNA. And then from RNA to proteins. And so we are made up of proteins.

In other words we eat food and that food is going to be reassembled to make us

In other words you are made up of proteins. And those were made up of amino acids. And so just like when you start to cook pizza, and if you want to cook pizza you're basically going to have to get all the ingredients together and then put those together in the right order to make a pizza, same thing works inside you. The DNA is going to tell your body how to organize the amino acids into those proteins. And those are eventually going to make you.

And so if we talk about that cooking analogy, basically the cookbook, if we're cooking in the kitchen is going to contain a bunch of recipes to make a number of different foods

The chef is going to pull right recipe out, or you could copy it down on a little index card, and then you bring it to the kitchen where you take all these ingredients. And then you put them together correctly to make pizza. And so if we switch to the next slide, what's been replaced in our kitchen. Well, the cookbook is going to be like the DNA.

It sits in the nucleus

It's protected. The chef has been replaced by a number of different ribosomes. The recipe is now messenger RNA. And if I were to do this accurately, I should have, you know, hundreds and hundred of different index cards. One copy of the DNA in a cell but hundreds of copies of the messenger RNA. What are the ingredients then? Those are going to be the amino acids. And we're going to put those together in the correct order and then we're going to make protein. And that protein makes you. This process that I'm describing is called the Central Dogma. And the central dogma was developed by this man, Francis Crick. So after Watson and Crick came up with the structure of DNA, he spent years working out how this actually works. And so the process, he called central dogma. Basically what we do is we take the DNA. DNA's going to have sections of it which are called a gene. And the gene is going to code for a specific protein. And so basically we'll copy down that gene into messenger RNA.

And that process is called transcription

Transcription is going to take place in the nucleus. And so all of this up here is going to take place in the nucleus. And this down here is going to take out in the cytoplasm. And I'm talking about eukaryotic cells like you. So basically we'll copy down that gene into messenger RNA. We'll manipulate it a little bit. We're going to modify it a little bit. But basically once we've done that, then that messenger RNA is going to move out through one of these nuclear pores. It'll going to grab on to a ribosome and then it's going to make these things. Proteins. Proteins, that process is called translation. And so basically the way I remember it is script in transcription stands for to write. And so we're writing down the message of the gene into messenger RNA. And so it's a message. And then that messenger RNA is going to go out here and we're going to have a number of amino acids that weave together. And the we're eventually going to create something like this, a protein. Now what does that protein make? That protein makes you. In other words you're made up of a bunch of different proteins. Where's the recipe book for the proteins inside you? That's going to be in the DNA.

In the nucleus of every one of your cells

Okay

So let's get to more specifically how that works. If we're talking about eukaryotic cells, remember all of our DNA is going to be contained within a chromosome. And so that chromosome is a bunch of DNA that's wadded up or it's wrapped around histone proteins. So if we unwind it you can see that double helix. But if we really unwind it what you'll find is there's going to be a message on either side. This enzyme is called RNA polymerase. It's going to move down that DNA and it's going to copy the information in the DNA. And so if we've got a C here, that's going to be a G here. So we're going to have complimentary bonding and we're going to create the transcript. It has the same information as they information that's found in the DNA. And then we're eventually going to lose that RNA. And now the nice thing about DNA is that it can zip together, because there will be hydrogen bonds between the two sides and now that gene is protected within the DNA. So if we go through that in the steps of transcription this would be RNA polymerase. RNA polymerase is going to grab on to the DNA. There's a number of transcription factors that are going to allow that to occur. Here's our gene. Then as the RNA polymerase is going to move down that DNA, you can see that it's creating a copy behind it. And that copy is called messenger RNA. So this is our messenger RNA. And if you look as RNA polymerase takes off, we've left the message behind and the DNA zips back together again. And so we have this initiation, elongation and then finally termination and the creation of that messenger RNA. Now in us we're going to do some things to it. We're actually going to put a 5 prime cap on one side. We're going to put poly A tail, which is just a bunch of adenines in a row. Another thing that we'll do inside us is that we're going to get rid of introns.

Introns are sections of that that don't actually code for a gene

So we'll get rid of those. And the we'll splice together that messenger RNA. But basically what we have when were done with transcription is some messenger RNA. Where does that messenger RNA go? It's going to go outside of the nucleus and it's going to go into cytoplasm. What's going to occur there? That's where we're actually going to take that recipe or we're going to take that message and we're going to make a protein out of it. We're going to build that out of amino acids. Okay. So how does translation work? Let's kind of orient ourselves because this diagram seems crazy. Here's our messenger RNA. So this is going to be our messenger RNA right here. And so it's moving through a ribosome. So a ribosome is where we make proteins. It's going to have two parts to it. It's going to have a small subunit. That's this bottom part. It's going to have a large subunit on the top. And then the messenger RNA is going to flow right through it. Every three letters in the messenger RNA is going to code for one amino acid. And the reason why is since we have 4 letters in DNA, 4 letters in RNA, A T C and G or A U C and G if we're talking about messenger RNA. Every three letters are going to code for one specific amino acid. And the reason it's every three letters is it gives us enough variety that we can cover all of the amino acids. So speaking of amino acids, where are they? The amino acids are going to be these little balls. And they're on top of another type of RNA. That's called transfer RNA. Transfer RNA's job is to transfer amino acids from the cytoplasm to the ribosomes. So we can attach them on to this growing polypeptide chain which is going to become this protein. And so basically what does a transfer RNA do? Let's just kind of look at one. It's going to grab it's amino acid right here. And then when it's its turn to go to the ribosome it's going to bond to the ribosome like this. And then it's going to drop off it's amino acid. And so it's basically dropping off this amino acid. It's then going to flow out into the cytoplasm to grab the next amino acid. Now each tRNA is going to grab a specific amino acid and it's going to have three letters on the bottom of it. We call that the anticodon. That's going to bond to the codon that's found in the messenger RNA. And so basically this occurs over and over and over and over again. Until it gets to a stop sequence on the end and then we're done with that protein. And so I'm going to start this animation over here. And so basically let me kind of talk you through it. This down here is going to be the small subunit. This on top is going to be the large subunit. And then we can see that we have all of these, they're blue, these dark blue, are coming in and they're actually bringing their amino acids with them. Now there's an enzyme that attaches that on. But basically these dark blue tRNAs are each dropping off an amino acid. And then they're taking off into the cytoplasm to pick up another amino acid. You can see right here that the messenger RNA that came from the nucleus is just feeding through the middle of that ribosome. And it's a site where we can actually have the tRNA come in. Now if we watch this animation here, this is a ribosome that's bound to the endoplasmic reticulum. And so it's going to attach to the endoplasmic reticulum. And that growing protein that was growing inside that large subunit is actually going to grow into the middle of this endoplasmic reticulum. And so we modify it or do things with it. And so basically this is translation. So translation, if we go back to our analogy again of the cooking, the cooking analogy, basically the ribosome serves the purpose of the chef. And so it's taking together all these different ingredients. All these different amino acids and putting it together to make a protein. So we're translating that message into a functional protein. You can see the protein coming out on this side. Okay. What I'm going to try to do here is actually decode a gene. So we've got a gene found within this stretch of DNA. So this is a double helix. So we have complimentary strands. And so basically what I'm going to do is the process of transcription. So I'm going to go from DNA, DNA to messenger RNA. And then I'm going to translate that message and I'm going to go from messenger RNA or through the process of translation. I'm going to go to the amino acids found in the proteins. Okay. So basically I'm going to play the role in this first line of RNA polymerase. So in the nucleus RNA polymerase is going to look what's at the DNA and it's going to put a complimentary RNA. So in the DNA A goes to T but when that unwinds the T will actually go to A in the messenger RNA. T goes to A. A goes to U. Remember we only have Uracil in messenger RNA. G goes to C. C goes to G. And so if I just keep going, this right here would be an A and a C and a G. And this is going to be a G and an A and a G. And this is going to be a C and an A and an A. And then this is going to be a U and an A and an A. And so every three letters in this messenger RNA is going to be what we call a codon. Because it codes for a specific amino acid.

Now if we want to do the actual translation and figure out what amino acids are created, well I can't do this from memory

I have to use one of these standard genetic code decoders. Some of them will be circular. Some of them will be like this. But basically what you do is you look at the codon in the messenger RNA.

So A U G

And then I just find that down here. So here's A U G right here, so that's going to be methionine. So methionine is going to be the first amino acid. Now methionine is special because it also starts all genes. All genes are going to start with methionine. Sometimes we trim that off later. But basically that's going to be our start sequence. Let's go to the next one.

A C G

So I find A C G. This is threonine. So that's going to be like this.

If we go to the next one it's G A G

So G A G, that's glutamic acid. So that's going to be Glu. If we go to the next one it's

C A A

So let's find that. C A A. That's glutamine. So that's going to be Gln. Then our last one is going to be

U A A

And so when I find that you can see it's right here. U A A. That's going to be a stop sequence. And what does that mean? Well that't the end of the gene. So that's not going to code for an amino acid. It'll actually put in a release factor so the whole thing can break out. And so this is going to be our first amino acid. Our second amino acid. Our third amino acid. Our fourth amino acid. This whole thing then is called a polypeptide. And again it would fold into a specific protein to do a specific job.

Now most of them are going to be much longer than this

But what I've shown you is how DNA becomes messenger RNA. Amino acids will eventually form proteins. And now that whole thing is eventually going to make you. Because you're made up of proteins. And so that's transcription. That's translation. And I hope that's helpful.

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