Model Organisms

Hi in this video, we're gonna be talking about model organisms. So model organisms are organisms that are commonly used to study biology. So they typically have certain features that make them exceptionally useful for studies. So examples of this include organisms that divide quickly or organisms that have transparent bodies. So you can actually look in and see different structures that are inside the body or they're ones that are really easy to genetically manipulate. And so the reason that we can use model organisms to be able to examine all organism biology or specifically human biology is because every organism is descended from an ancestral cell. So we all came from the same original cell. So we all have very common features that are associated with um our survival and disease. So um there is pros and cons to this. So the pro is that genome comparisons between organisms can reveal diversity and sizes but they all have similar genes. So um we refer to this as conservation. So there's similar genes and similar gene sequences between all of these different organisms, even though they can be quite different. Now. The con to the fact that every organism is descended from ancestral cell is the idea of genetic redundancy. So over time throughout evolution, um multiple gene versions have arisen within an organism. So this means that if we have a gene a within any organism that can be an A. One and a two or a three and they all have similar functions. And so when we try to use model organisms to study a particular function, we can have trouble because if we make a mutant, so mark this here. So we make a mutant in a one. And we don't see an effect. It could be because A two took over. And so there's no effect. And the genetic redundancy really complicates our studies but we still use them because it's really the best we have and they are great tools to study biology. So in this image I wanted to just look at what it means to be conserved in terms of a gene. So this is actually the protein sequence of a histone um histone protein. And you can see that from champs two rats to humans that this sequence is very highly conserved and that in the portions where it differs usually, you know there's one or two options but that is just not entirely diverse. And so these genetic conservation conservation between these organisms allow us to use model organisms to study human biology or disease biology or just biology of organisms in general. So let's move on to the next concept

So in this video we're going to just be very quickly going over different model organisms that are used to study biology today. So the first is coli E. Coli um And this is used to study pro carry ah tick biology. So the genetics with E. Coli are basically the same throughout all organisms. They rapidly divide which allows them to be studied quickly in labs. And then also scientists can actually manipulate a coli to replicate D. N. A. And actually grow proteins for experimental use. So we wanted to study the function of some protein. We can grow it in a coli and use it and sort of extract that protein and use it in other experiments. So this is just an example of what a coli looks like. Now if we go to the next page we can see that yeast um which right here is just the scientific name for it is used to study basic eukaryotic biology. So the reason this is used it's a single eukaryotic cell has a small genome and it can be grown in a laboratory um They divide quickly about once every two hours. And they're really easy to manipulate genetically. So genetic, entire genetic screens to look at specific genes that cause certain types can be done by just mute organizing the whole thing. So you can pretty much just kind of put any kind of mutation on here and this can be a chemical, it could be UV light, there's many different types of way to organize D. N. A. Um And then say okay well um which uh you know cells are smaller or which ones have these weird bumpy things in them. Um And genetic screens are big um reasons why yeast are used to study biology. Now if we go down and look at another one this is the next two are really common but we start getting more advanced here. So joseph e lia Melanie gaster. This is a fruit fly and has been used to study the mechanisms of genetics. Um So these are things like chromosome of biology um patterning during development. They also divide fairly quickly for such a complex organism about two weeks. Um They have a new batch of offspring. Um And so mainly fruit flies are used to study genetics. Gene identification and function. Now if we look at c elegance um this has actually been used to study cell differentiation and development. So these are worms actually little transparent worms. I'll show you a picture of them in just a second. But we actually one of the really cool things about C. Elegans I think this really blows my mind is that the entire sequence of events is known from the single Zygote which is the first cell of really an organism to the final 959 cells that make up the worm. So every cell division that happens from this single Zygomatic cell to 959 cells all of them are known. We can say you know this cell divides into one and two and I know exactly which of the 959 cells. Cell one becomes. Um and I think that's really neat. It really helps us understand the mechanisms involved in development. Now we can also use the elegance to look at human development because 70% of human genes are found have warm counterparts. Um and then usually we create like the flies we create and yeast we create mutants to study them. So here's an example of the fruit fly and here's an example of C. elegance. Well again it's here which is a transparent worm. Um So let's let's continue on with our model organisms. So Arab top sis is used to study plant genetics and development. So this is a weed of little flower and we'd hear it can be grown indoors um and has tons of offspring here thousands and 8 to 10 weeks. This is fairly quickly for laboratory science. Um but we can also, I mean I know we use it to study plant biology but it does have universal features to all organisms. And it contains about 26,000 genes which is around the same number as humans who have 25,000. So really comparing how these genes are organized and um express can help us really determine you know what makes an organism complex. Um if it's not just the same number amount of genes. So moving on we're gonna talk about zebra fish and frogs which are used again to study developmental, develop mental biology. So zebrafish here's their scientific name are actually transparent the first two weeks of their development. So it's really easy to inject genes into their embryo and really look and see the internal structures that change. And they're very easy to maintain. You can keep a ton of them in an aquarium and they reproduce rapidly. Frogs are used to study development because they have extremely large eggs which are single cells. And so we use frogs and their eggs to study cell division. Um And also this unique thing called whole genome duplications, which is exactly what it sounds like. A duplication of the entire genome, which is really common in different frog species. So here's an example of a zebra fish and here's an example of um of the frog. And you can see that these are two separate species that have underground gene duplication. So this one is larger because it's had its genome duplicated and this one is smaller now. Um Not quite the final but we're getting very close is mice. Um And these are used to study disease. So why do we use mice? They reproduce quickly? They produce a lot of offspring, but very important is 99% of their protein coding genes um are very similar to that of humans. They also have extremely similar immune systems. And the immune system is what allows our bodies to fight off disease. So they're extremely useful to studying disease. So we can use them to mimic human disease, especially human disease caused by certain genetic mutations. Um, so we can induce these mutations into the mice and see and watch them develop the disease so that we can study it. So here's an image of a laboratory mouse. So now let's move on.

So so far we've been talking about larger, entire organisms to study biology, but now I want to focus on some smaller aspects that we can use to study cell biology. So the first is cell culture and this is actually growing human or other cells in a plastic or glass dish, actually inside of a laboratory. So this is used to study cellular mechanisms like signaling growth division and gene expression. Now growing cells in a dish there can be many type of cells. You can grow, you can grow everything, but you can grow a lot, but growing them in a dish because it's happening in glass is called typically called in vitro, whereas studies happening in living organisms is called in vivo. Now I want to have a huge disclaimer here because there's a kind of a controversy over whether cell culture classifies is in vitro or in vivo. So the reason is because cells are living. So any studies you do in them is technically in vivo because they're living. Um but also they live inside glass or plastic dishes. So it's also in vitro Now, for me, I like to think of cell culture as in vitro, whereas in living organisms is in vivo, but your professor probably has their own opinion. So you should ask them and to figure out which um which one they prefer, especially if you can see these coming up in class or in your lectures and you think they might be on a test. So make sure to double check of which one cell culture is used by your professor. Now, the reason cell culture is used is because you can you can treat these cells with nutrients or proteins or chemicals and just see how they react um on a molecular level. And this is important because sometimes these Kemah can be really harmful to organisms. Um but they but for sales it doesn't necessarily matter because sales we don't consider as you know, as important as actual living organisms. And so what you can see here is these are cervical cancer cells from a human, they're called hela cells and they're growing in cell culture and the blue here is actually the nucleus. So cell culture also gives us a way to study particular human cells in a way that studying other organisms doesn't allow us to do. So another way they're smaller way to study biology through viruses. The viruses are used to study cell biology now waters the virus, the virus is a non infectious are non living, excuse me, non living infectious particle. And they are composed of protein um surrounding genetic material. So these are really important because they can actually be manipulated to add DNA to cells. Um so the genetic material that the virus has um can be replaced with whatever genetic material scientists want. And this is especially true with retroviruses which are RNA viruses that can actually integrate the genetic material they carry into the host cell's chromosome. So this is really important for scientists because if we want to see what the effect of a particular gene mutation is on a cell, we can just replace the retroviruses genetic material with this, whatever genetic mutant we want and infect a cell with it, and then that genetic material will be integrated into the host chromosome replicated and expressed when before it wouldn't have been there. So this is a really important way to study cell biology. So in this image here, you can actually, this is an HIV retrovirus and you can just see the structure here. Um there's nothing too complex about it. It's just just the virus particle. So now let's let's move on.

Which of the following organisms is often used to study developmental biology?

• A. E. coli
• B. Yeast
• C. C. elegans
• D. Retroviruses

Frogs are often used to study development because why?

• A. They have unusual genetic systems
• B. Their eggs are large enough to see with the naked eye
• C. Their embryos are transparent
• D. They contain a small number of chromosomes

Which of the following organisms would be the most difficult to use when performing a genetic screen?

• A. Yeast
• B. E. coli
• C. Zebrafish
• D. Mice