Okay. So now let's talk about some of the introduction to the mechanism of regulation. The lytic cycle and the lysogenic cycle genes are actually physically separated on the chromosome. Now, keep in mind, this is a circular chromosome that we're talking about. And so, I'm showing it as linear, but just keep in mind that this is actually curved. Not that it really matters, other than just, like, making sure you're aware that, you know, bacterial chromosomes are circular. So the lytic cycle, promoting the lytic cycle, has the o, p, and q genes. And the lysogenic cycle has two genes called int and cI. And so, those are two important genes, but the genes that we're mainly going to be talking about are regulatory genes. And they sit in between the lytic and lysogenic cycles, and here they are. Each one of them has different functions and is super important. We'll go through each one individually. But, this is what it looks like. So you have the lysogenic cycle genes over here, the lytic cycle genes over here, and you have all these regulatory genes here. Now, keep in mind we've been talking about operons, and remember, what does every operon have? It has a promoter, an operator, a repressor, and the genes. So although this isn't technically an operon, some of these may be operators, but the regulatory genes aren't operators. But each one of these genes, even though I'm not showing it here, has a promoter, an operator, and is a gene itself. Right? Also, all of them have terminators, as well, which I don't mention a lot but terminate transcription. So there's a lot of factors here. So if I were to write all of these, it would get very confusing. Right? Because there would be a promoter, an operator, and a terminator, a promoter, an operator, and a terminator for every single one of them. And sometimes, it actually goes in the opposite direction depending on the gene. So I'm saving you this super confusing graph of promoter, operator, terminator for each of these genes. But during the regulation, some of them get activated or repressed, and so I'm going to be writing the ones we're talking about as we're going. So let's just get started and delve in. The first two mRNAs that are transcribed are controlled through different promoters. The first gene that's transcribed is n and the second is cI. So n cI. The n has its own promoter called pL and it has a terminator called tL. And the cro has a promoter called pR and it's terminated by a terminator called tR1. And these genes are actually transcribed in reverse of each other. So the other thing you need to know, I'm going to show you an image, but the other thing that you need to know is that the n protein is a special type of protein called the anti-terminator protein. Now this isn't an anti-terminator structure when we talked about the tryptophan operon. This is a protein, so it's completely different. But it has the same function. So as an anti-terminator, it allows transcription to take place. What it specifically does is it allows transcription to transcribe past the terminator. So remember, the n gene and the cro both have terminators, and the N protein, when there's a lot of it, will actually bind to these terminators and block them, allowing transcription to take place. So, what this looks like—and this is how this really gets started. So you have these two mRNAs, they get transcribed first. And I don't know, my pen isn't working. Anyway, you can kind of see. Oh, I don't know why it's not working. Anyway, so the n and the cI get transcribed first. And each one of them has a promoter. Right? You can't follow my thing. Each one has a promoter and a terminator. And I've labeled them different colors, so you can see. Now they're actually transcribed in different directions. Right? Because the promoter starts transcription. So the cI is transcribed this way, and the n is transcribed the other way, which I've shown by these arrows. Now, there is n and cI protein both produced. Right? So I'm only showing n here, but if I were to write Cro all down here, there's cI protein being produced. But really what happens is a lot of n protein gets produced, and those come in and bind to both terminators. So I've shown them here as the red and the big bolded red. They're binding to the terminators. What happens is that allows for this arrow, this transcription to transcribe all the way to the end. So all the way to the lytic cycle genes and all the way to the lysogenic cycle genes. But in the meantime, what it does is it allows for the transcription of these two proteins here, c2 and c3. And so I'm going to talk about, and then over the next pages, what c2 and c3 do to regulate about which one is chosen? Because right now, both are being transcribed, and that's not what we want. What we want is to choose one over the other. And so, c2 and c3 are going to help us choose which cycle is going, which genes are going to be graded. But essentially, this is the first thing that happens. n and cI are transcribed, and a lot of n is made, and that binds to the terminator and that causes transcription to occur past the terminator. So with that, let's now turn the page.
Table of contents
- 1. Introduction to Genetics51m
- 2. Mendel's Laws of Inheritance3h 37m
- 3. Extensions to Mendelian Inheritance2h 41m
- 4. Genetic Mapping and Linkage2h 28m
- 5. Genetics of Bacteria and Viruses1h 21m
- 6. Chromosomal Variation1h 48m
- 7. DNA and Chromosome Structure56m
- 8. DNA Replication1h 10m
- 9. Mitosis and Meiosis1h 34m
- 10. Transcription1h 0m
- 11. Translation58m
- 12. Gene Regulation in Prokaryotes1h 19m
- 13. Gene Regulation in Eukaryotes44m
- 14. Genetic Control of Development44m
- 15. Genomes and Genomics1h 50m
- 16. Transposable Elements47m
- 17. Mutation, Repair, and Recombination1h 6m
- 18. Molecular Genetic Tools19m
- 19. Cancer Genetics29m
- 20. Quantitative Genetics1h 26m
- 21. Population Genetics50m
- 22. Evolutionary Genetics29m
12. Gene Regulation in Prokaryotes
Lambda Bacteriophage and Life Cycle Regulation
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