MBG Transcript from 10:23:24 PDF

We are not getting through this. We are not rushing. We are not behind. I want us to hit these messages. RNA and DNA have very similar objectives. I want us to understand the molecular processes, structures, and comparison between the two. Gene expression is making RNA. Whether it is a non-coding RN...

We are not getting through this. We are not rushing. We are not behind. I want us to hit these messages. RNA and DNA have very similar objectives. I want us to understand the molecular processes, structures, and comparison between the two. Gene expression is making RNA. Whether it is a non-coding RNA or a coding RNA, an mRNA, a gene encodes a product. That product always starts as RNA of some type. Our direct line from DNA to product is DNA to RNA. RNA has higher order structures. The main difference between RNA and DNA is going to be in what bases make it up, but also what nucleotides. What is a nucleotide? Base sugar phosphate. It is a different sugar. DNA polymerase sees DNA nucleotides. RNA polymerase sees RNA nucleotides. Ribose sugar for the RNA, deoxyribose sugar for the DNA. Even though the machinery seems similar, polymerase, they are strikingly different. Classic difference between DNA and RNA that you are always told. What are the bases? A, C, C, G for DNA. A, U, C, G for RNA. Still true. Do not tell me one is single-stranded and the other is double-stranded. That is not a real difference. RNA is usually single-stranded, but as we know from single-stranded DNA viruses, DNA can be single-stranded as well. But what is the nature of being double-stranded versus single-stranded actually mean? Mutability. RNA is even more mutable than DNA. It is less stable. Classically speaking, we did not think RNA was stable at all. We used to think you had to work on it on ice in a special room in order to actually be able to see it. Turns out it is a little bit more stable than that. You can work with RNA at room temperature under some procedures, but it is far less stable than its DNA counterpart, especially double-stranded DNA. RNA makes higher order structures with self and others. Like proteins, there are multiple levels of structure, primary, secondary, tertiary. Secondary structure for RNA is complementary base pairing. I am actually going to have hybridization with self because I am going to have A-U, C-H-E, and I am going to see a partner to that. Common structures include loops and hairpins, and also hairpin loops. I am literally folding in three-dimensional space, and this folding can get complicated, but will be essential to the function of that RNA. RNA need to fold to do their job. We have lots of types of RNA. What type encodes proteins? mRNA. We have a lot of non-coding RNA. We are going to categorize them as structural or regulatory. Structural RNAs include your tRNA, your rRNA. They have a function toward building other molecules or forming the machinery to build other molecules. These can include SNO RNAs and our SN RNAs. These are all structural. They provide sequences. They provide carriers for things. They are part of building other things. Regulatory RNAs regulate processes. Our long non-coding RNAs can function to prevent proteins from doing their job. SI RNAs, small interfering RNAs, can actually break down the ability to translate a piece of mRNA. It interferes with translation, can label material to be broken down. I don't expect you to be able to do this whole list, but I do want you to be able to recognize the difference between structural and regulatory. How do we actually get these things? Well, there is actually process. We have a key need for these in human systems. If they don't work, if we don't have them, that can lead to disease. So looking at all of this, I just want you to get a picture of, please do not spend a ton of time with this slide. I just want you to get a picture of, just because you don't make a protein doesn't mean that you don't have major processing or a major role in these processes of molecular genetics. There's a lot more going on with each of these than we even have time to cover. mRNA is the one we've got to spend the most time with, because mRNA gives us the instructions for proteins, and proteins are doing the work. Proteins are your enzymes. They're all of the activity. Eukaryotic mRNA is monocystronic. You've got a piece of mRNA. It's making one product. We can process it to turn that one product into having multiple outcomes, but it's still just one gene. Prokaryotic and other, like chloropast mRNA, that is polycystronic. One sequence will often give me multiple proteins that are all working together in the same process. For example, if I have three parts to a particular protein, part one, two, and three, my polycystronic mRNA will make those three parts so that our final functional enzyme has all three parts. Polycystronic mRNA is very, very effective. Part of the reason why it's so effective is because it allows for coordinate regulation. Prokaryotic material is all in the same compartment because prokaryotes lack membrane-bound organelles. I do not separate transcription and translation, so it makes sense that those two things are coordinated because they're not separated. But in eukaryotes, what do we have? We have membrane-bound organelles, specifically the nucleus. DNA is where? The nucleus. So transcription is where? The nucleus. Where's translation? Cytoplasm. So I can't have that coordinated regulation to the same degree, but I have remnants of it. RNA Paul II, which is part of our transcription machinery, can do jobs that look very similar to our prokaryotic polymerases. It can move past the point of the end of our mRNA and make other things, very much like a polymerase running across a segment of DNA to create a polycystronic mRNA molecule. All right, we just got a few minutes and we're just going to start this concept. This is a review of everything I just said. RNA product is typically single-stranded, contains uracil. It is only part of the genetic material. It's only a gene product, not the whole DNA. Transcription is really unique. And RNA polymerases are really fantastic. What did DNA polymerase need to do its job? It needed the material open. It needed a landing pad. It needed something else to stabilize it all before it could do its job. RNA polymerase does it all in one. It's going to land on double-stranded DNA. It's going to open that DNA, and it's going to stabilize it as it makes its product all in one. So transcription for this is complementary in the same way. Polymerase is still doing the same job, but it doesn't require a primer. How does it know where to go then? How does it know where it should be? It's going to need a promoter. This is a sequence of DNA telling it where to land. Same three categories. Start, make the molecule longer, stop. Initiation, elongation, termination. Same three broad categories. Each of these steps has key components. I want us to understand that in terms of RNA Paul II, we have a lot of similarity across organisms, but we are going to be playing a huge role in terms of initiation. Initiation is going to be critical to this. Find the right spot. Open the DNA. Use a template to make a product. It's a polymerase. That's what we do. Free the strand I just made. Fall off. I've got to get off this DNA. If I'm there always, I create a problem. Make sure the DNA closes. I don't need extra stuff once I'm there. Once I'm on the genetic material, if I'm RNA polymerase, I'm actually hard to get off. I am hard to remove. So controlling me is all about controlling my association. That's where enhancers and silencers come into play. Enhancers help me land. Silencers keep me from landing. Make sense? We regulate at the level of transcription. I think this is a key place to stop because we will start in with those promoters. We will likely finish all of this and the next one on Friday because it's all tied together. One is regulation of transcription. There is a slight subject change. I think the way it was written in your syllabus left off the introduction to gene regulation part, but that's essentially what Friday's lecture delves into. Questions or concerns? Okay, so in my last 10 seconds, I have one little announcement. Please remember that next Friday is a campus mass. We do not meet in person, so there will be some materials and I'll make sure I release that gene code lecture hopefully at the end of this week so you have access to those pre-recorded materials. That was it. Thank you so much. Happy Wednesday.