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Cell Biology

Learn the toughest concepts covered in Cell Biology with step-by-step video tutorials and practice problems by world-class tutors

20. Cancer

Overview of Cancer


Overview of Cancer

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Hi in this video, I'm gonna be telling you about an overview of cancer. So what is cancer? Cancer is a disease, we're probably all familiar with it. But it's caused from mis regulated or unregulated cell division and the cell division occurs rapidly and usually way too much. And because there's all these cells dividing and they shouldn't be, it forms these structures known as tumors and these are just kind of big cell masses from a bunch of cells that have just continually divided after they shouldn't have. Now there are two types probably familiar with these terms the versus benign and this is a tumor that remains confined to its original location. So there's a tumor there but it's just sort of living its own life. Even if it shouldn't be there, it's not really bothering anything around it. Then you have malignant tumors which are very different because malignant tumors and start to invade surrounding tissues and can actually spread throughout the entire body into very distant organs and tissues. And this is called metastasis. So there are three main types of cancers. Now, obviously each one of these types have so many different cancer subtypes in them. But just to give you an idea, we have carcinomas and these are going to be cancer is found in epithelial cells, overwhelming majority of all cancers. Then you have leukemias or lymphomas and these are cancers of the blood for leukemia or immune system for lymphoma and a much smaller proportion here. 7%. And then you have star comas and these are cancers of connective tissue and these are extremely rare. They do happen. Of course they're on here. But I mean if we add this up, that's around 3% of the rest of the cancers. So here's an example. So here we have a benign tumor and you can see the tumor here in bread is really combined. It's just this nice clean circle and you could go in there and cut that out. And you know for the most part it would be all fine. But the millionaire tumor looks much worse. It has much more jagged um regions that started to invade down um into surrounding tissues. And obviously it's not gonna be good for the patient with the middle aged tumor. So but cancer. So what causes cancer? What cancer can be caused by many factors will go over a few of these and other videos. We just want to hit it real quick here. The first one. The term that we're probably most familiar with are carcinogens. And these are substances that cause cancer. Things like tobacco which is associated with 30% of all cancers. I mean think of how, how few, we have 30% less cancer if we got rid of tobacco because tobacco is known to cause cancer. And so we figure out carcinogens and we identify what things cause cancer and what things don't through a field of study called epidemiology. You may be familiar with this if you've done anything with public health. But epidemiology is a scientific field which studies disease in human population. So for the epidemiologists that study cancer a lot of times what they do is they look into the United States population or your state's population and say okay what is everyone doing? And which one of these things are causing cancer? So those are called carcinogens. Now the important thing to realize here is we know typically that cancer is caused by DNA mutations but um cancer is not really caused by one mutation. Usually a bunch of mutations have to accumulate in order to cause cancer. So um we call this tumor initiation when some type of genetic alterations or mutation leads to abnormal cell proliferation and replication. So notice I didn't say cancer here this is abnormal cell proliferation, right? And that's usually how cancer begins. But it's not cancer yet. It hasn't formed cancer until it's formed a tumor and meets a variety of different properties which we'll talk about. But um tumor initiators can actually be handled by the body sometimes even if they're leading to cell proliferation. But what happens is then you get tumor progression. And that is when the tumor cells gain more mutations because you're getting more mutations, you're already over proliferating these um mutations accumulate and that allows these cells to really divide unchecked that causes tumors. Now the mutations are generally found within two types of genes. We'll just give an overview. I'll talk more about them later. But the first is called an uncle gene. Now an aqua gene is a gene that when it's mutated. Okay so uncle genes are mutated genes that cause cell growth when it is before it's really become an aqua gene. We call it a proto oncogene. And this is a that can very easily become an oncogene if it has additional mutations. So aka jeans um mutated genes that cause cell growth and tumor suppressors are genes that normally. So when they're not mutated suppress cell growth. Um And so obviously when you mutate that you mess up that suppression and can lead to cell growth as well. So here we have an example of this. This is an ankle jean. So we have some kind of cancer causing agent. What do you remember what we call these? Right so these are gonna be carcinogens and they somehow enter into the cell, they come in, they hit the D. N. A. And they cause DNA damage. So here we have a mutated gene. And so this is what we call this a proto uncle gene. So this is a gene that has a mutation, it can very easily become an uncle gene. And now you see that it has it either gets more damage or there's some something weird happens to it. This now becomes an activated oncogene and that can lead to the development of a cancer cell. So um tumor cells have a variety of characteristics which we use to determine whether or not they're cancerous. So tumor cells present with certain characteristics. The first is we say tumor cells are genetically unstable. So what that means is that they accumulate mutations at a very rapid rate. So our cells normally really hate accumulating mutations and they don't do it essentially or else we'd be covered in tumors all the time. So but cancer cells accumulate a lot of mutations because they're genetically unstable and can do that. We also refer to tumor cells via contact inhibition. So what contact inhibition means is that sales have contact inhibition. So when cells grow and they eventually they grow so much that all of their sides are touching other cells. So when their entire plasma membrane is touching other cells they're gonna stop dividing because they realize, oh I have no place to go. Because because all the sides of me are I'm surrounded by cells so I'm not going to divide. So they stop dividing when they're touching other cells that's called contact inhibition. But cancer cells or tumor cells will actually lose contact inhibition. So even though the plasma membrane there surrounded by all these other cells, they continue to divide. And so then they just grow on top of each other and that forms this tumor over time. You may see this in your book as Anchorage independent growth. But it's the exact same thing then um they also have to undergo this term called angiogenesis angiogenesis means it's the formation of blood vessels. So of course if you have all these new cells that are growing in a tumor, they're going to need some type of um supply of oxygen and nutrients. You're going to need a blood vessel to get it there. So tumor cells often will undergo angiogenesis and create blood vessels where they shouldn't be in order to supply those nutrients to the tumors. And then also cancer cells. And tumor cells have some type of defect and apoptosis or cell death. Right? Because these cells are growing, they're not dying, they're accumulating forming this tumor. So there's something going on. Something wrong with the cell death or the apoptosis pathway. So I know that was a lot of information but hopefully it was very simple, just kind of an overview of the processes of cancer. So with that let's now turn the page.

Which of the following is not a characteristic of tumor cells?


Which of the following genes normally suppress tumor growth, but when mutated allow for tumor growth?