 This section is on the central dogma of molecular biology. Central dogma means main idea. Molecular is at the level of molecules like DNA and biology is the study of life. So, biologists feel like this is a main idea to biology at that level, to life at that level, because it is, it's so important to making us who we are and making us unique from each other. So, the boil-down principles of the central dogma are that genetic information is stored in DNA, transcribed into RNA and translated into proteins, which express traits like that you can see or have tested like freckles or blood type. Throughout the course, you should have learned a lot about DNA structure and function, and so now we're going to talk a little bit about RNA, which is another type of nucleic acid to transmit genetic information. There are some differences, hence the names being different. DNA has that double helix structure. RNA is single-stranded. They have a different sugar, still both five carbon sugars. DNA, of course, is deoxyribose and RNA is ribose, and then the slightly tricky one, the nitrogen-based thymine or T that exists in DNA doesn't exist in RNA, so a chemically similar nitrogen base is called uracil, and so you'll have that when we talk about RNA. Now, to get a little bit more complicated, within RNA there are three types, and they're sort of arranged here by level of importance. Messenger RNA or mRNA carries the message of the DNA transcript from the nucleus to the ribosome. Transfer RNA transfers the amino acids, which are the building blocks of protein, to the ribosome. So remember, amino acids get peptide bonded together to make a protein at the ribosome, and ribosomal RNA is the easiest one to keep up with because it just coils up to make part of the ribosome. Okay, so then I'm going to go to the next slide, and here's our whole process of protein synthesis or gene expression. And the reason why these processes exist is because they're sort of a language barrier in ourselves, right? We have DNA inside of the nucleus, the A, C, T's and G's that we just talked about, that you've learned about a lot throughout the course, and then we have RNA which is fairly similar language, but there are some differences, like American English versus British English. So replication is just what, when the DNA is copying itself, to make sure that all the new cells have a master copy of that instruction book, and that takes place in the nucleus, and that you should feel comfortable with from the last section, and it's not really a key component in the actual gene expression process, but except that you have DNA there to use as a template. So, the first step of the gene expression process is transcription, which takes place in the nucleus as well as replication did. Okay, and that's important because DNA is imprisoned inside of the eukaryotic nucleus. It cannot leave. So it's all well and good if that's the instructions for the proteins you need, but if they can't get the instructions for the protein factory that is the ribosome in the cytoplasm, then how are those proteins going to be made? And that's where RNA comes in as a messenger to go into the DNA, transcribe that information, those instructions or blueprints for life, by getting the base pair information from the DNA transcript, except there's no T's in RNA. So you have to use you. We'll get to that some more in a minute, but so the RNA transcribes an RNA copy of the DNA information, takes it out of the nucleus to the ribosome where translation happens. Okay, so let's say in ribosome or sorry, it should be at ribosome, and you know that ribosomes are in the cytoplasm outside of the nucleus and that's why it's such an important thing to know because the DNA is trapped there. It cannot leave. So the RNA helps us get the information that we need. The messenger RNA is the one that carries the transcript to the ribosome and the transfer RNA are the ones that bring the amino acids to the ribosome. So if you're asked to work through a problem like this, like your instructor could give you a nuclear DNA segment, a small piece of a gene, more than likely they're really like hundreds or thousands of nitrogen bases, but just for work's sake, we use smaller examples and oh wait, I wanted to tell you one more thing about translation. Transcription, we talked about the two fairly similar languages, American, English, and British, English, vernacular. You don't need a translator to move between the two. You can usually understand each other pretty easily. However, RNA to amino acids are two drastically different languages and we do need a translator and I just gave you a little preview of that. It's called the mRNA code on chart. And I hope that it's not too intimidating because you don't have to memorize this. It should always be provided for you, but you do need to know how to use it. And it works similarly to a map or even GPS to a certain extent with a triangulation of three or more satellites. We're just triangulating from these parts that represent the nitrogen bases on the mRNA. So if your instructor gives you a DNA, a nuclear DNA sequence, T, A, C, A, G, A, I wish I had more space, but I guess we can go down like this. T-A-C-A-G-A C-C-A T-T-T and A-T-T, right? This is our example segment. It could be a thousand of these long, but we're just going to stop here. What's that? 15? Three five triplet codons of three. So the mRNA is red in groups of three called a codon um three nitrogen bases and everybody has slightly different ones. So that's what leads to all the cool diversity around there. But um, so your nuclear DNA segment is as follows. Your mRNA segment would be and I'm going to change colors and maybe I can do it up under it without a V kind of squish. Okay, so well, I'm going to go with it. So, um right out of the gate, T you know, you're like, oh, what's that confusing thing we have to remember with RNA? T pairs with A. That's the same thing as DNA. So you're not confused yet. But then you're like, oh, A pairs with T. But wait, there is no T in RNA. So you got to put U A U G U C U G G U A A A and U AA okay That's transcribing from the DNA language to the RNA language and you can do that yourself. You just have to remember the base pair rules. Okay, next is how when we use the codon chart and use the blue mRNA sequence that we have just transcribed to translate using the codon chart. So this part was transcription DNA to RNA and now I got to erase the DNA because we're finished with that. Oh, I got some of my RNA in the process. It was A U G, right? I'll just rewrite it. Okay, so our mRNA is U U G U C U G G U A A and U AA. All right, so I told you about how mRNA is read in codons or groups of three, not charging the spaces. The mRNA codon chart is in groups of three. Everything is done in groups of three. But if you notice there's some repeats on here and so that's why our genetic code is called a redundant code and it just makes it a little bit easier for us because some of the same some different codons code for sometimes even six different ones code for the same amino acid. All right, so the last thing we have to do is learn how to use the codon chart. So we have A U G and we're going to find the convergence of those letters. A is the first letter so we know that it's going to be in this row. This one's nice and color-headed, but they won't always look like this, but once you learn how to read it it'll be easy. Okay, so we know that we're going to look for our amino acid somewhere in this A row. Then the second letter is U so we know we're going to look for our amino acid somewhere in the U column and not only that, but in the convergence of the row in the column. So somewhere in there. Oh, I guess I could circle it right. Green somewhere in there because it's the A row in the U column and then we go for our third letter is G so we trace that over there and we have methionine which is the start codon. It's always new proteins start with methionine so just keep that one in mind. Okay, methionine start codon. All right, and next, UCU. First letter U, we know it's in this row. Second letter C, we know that it's in this column and not only that but the area where the column and the row meet and that's one of those redundant codes like I was talking about where they all code for serine so just to double check we go U, trace it over. It's serine. Okay, and G is the first letter of the third amino acid code. G is also the second letter. Another redundant code GGU. Glycine in this row somewhere. A in this column somewhere so somewhere where the row and column meet. Trace over the A for the third letter. Your chart's always going to be set up like this and I'm always going to tell you first letter, second letter, third letter. We came up with glycine and the last one, okay, our first letter is U in the U row. Second letter A in the A column somewhere in there. UAA, trace the A over and we get stop which just tells the transfer RNA to not bring any more amino acids so that means the protein's finished and can be released from the ribosome to go do whatever job it needs to be done. It can stay and within the cell or it can go outside of the cell. Proteins do all kinds of important stuff like provide structure, our chemical messengers like hormones, enzymatically speed up chemical reactions so proteins are a big deal and this process though daunting it helps to step back and look at it and get perspective like your cells are completing these processes way before you're even born so thankfully you don't have to teach them how to do it but it's cool that we can use science to find out more about how it's done and maybe errors and presenting sentences and think about all the applications for example medicine and just keep exploring so thank you.