Main content
Course: MCAT > Unit 6
Lesson 8: Cellular division- Cellular division questions
- Mini MCAT passage: Tyrosine-kinase inhibitors in cancer treatment
- Cell cycle phases
- Cell cycle control
- Loss of cell cycle control in cancer
- Mitosis
- Interphase
- Mitosis
- Comparing mitosis and meiosis
- Meiosis
- Phases of meiosis I
- Phases of meiosis II
- Cancer
© 2024 Khan AcademyTerms of usePrivacy PolicyCookie Notice
Loss of cell cycle control in cancer
Proteins like p53 and RB play a crucial role in regulating the cell cycle. These proteins, known as tumor suppressor genes, prevent uncontrolled cell division, potentially leading to cancer. The case of p21 is intriguing, as its absence can surprisingly trigger limb regeneration in mice.
Want to join the conversation?
Is having good handwriting a requirement for working at KA? lol(12 votes)- If you're one of the people making videos, it's probably highly likely that you need to have good handwriting so people can more easily make out what you're saying.(2 votes)
At1:05, wouldn't inhibiting CDK cause the cell to not enter mitosis and prevent cell growth? If so, how does that lead to cancer if cell growth is stopped, not overdone?(5 votes)
If the CDK is phosphorylated then it can't inhibit (or stop) the cell cycle. Continuous phosphorylation can result in increased rate of cell division without inhibition and this potentially cancer.(4 votes)
At0:44, when the speaker say, "...so it shows you how important P53 is. It's more important than chocolate.", wouldn't it be more accurate to add, "according to Science Magazine", because it was Science Magazine that named P53 the "Molecule of the Year in 1993", but there are probably millions of women and also many, many men who believe that theobromine ("the main ingredient in chocolate") is a more important molecule and possibly deserving of the title "Molecule of Eternity"?(0 votes)- Probably not. I think it's a fair assumption to say not constantly developing multiple kinds of cancer is at least a little better than chocolate. Especially considering the average lifespan without p53 would probably be in early childhood.(18 votes)
So basically through p53 the p21 protein is made and this prevents cyclin and this in turn doesnt phosphorylate Rb and therefore Rb CAN inhibit DNA replication right?(5 votes)
Although it might show in one study that the absence of the p21 gene in mice results in an increased ability to regenerate limbs, this might not be the full picture. The p21 gene, also known as CDKN1A, encodes a protein that regulates the cell cycle and prevents cells from dividing too quickly or in an uncontrolled manner. The regeneration of limbs is a complex process that involves the activation of specific pathways and the coordination of multiple cell types, and the genetic and molecular mechanisms underlying this process are still not fully understood. The ability to regenerate limbs is a characteristic found in certain species, such as salamanders, but not in mice or humans. The absence or alteration of the p21 gene may have other effects on the biology of mice, but it does not result in an increased ability to regenerate limbs.(4 votes)- What does the "p" in p53 and p21 stand for?(3 votes)
- The p in p53 stands for protein, and the 53 is for 53 kilo Dalton molecular mass.(2 votes)
- p53 and RB are both proteins that are both tumor suppressor genes that in their defective form can cause cancer because they can cause tumors to grow?(2 votes)
That is true! Just remember that they themselves are called tumor suppressor proteins; tumor suppressor genes are what code for them. :)(3 votes)
If a cell has somehow managed to divide with defects, would that mean the daughter cells will acquire those protein defects as well? This would mean the growth of a tumor, right?(2 votes)
depends. if its mitosis, then definitely any defects in parent cell, the daughter cell acquires. if its mitosis, some, not all, of the cells acquire the defects(2 votes)
- Can p53 be artificially synthesized in the laboratory?If so it can't it be injected into cells lacking it to prevent cancer?(2 votes)
It might slow cancer for a tiny bit, but eventually it'll degrade. The problem is that cancer cells can't generate p53 (among other tumor suppressor genes)(2 votes)
- What's the relationship between INK4A and Retinoblastoma gene?(2 votes)
1:05
Video transcript
There are other, higher levels of regulation that occur here and I started to talk about them when I mentioned our RB protein. So, control of the cell cycle occurs on a higher level with a couple of key proteins in addition to RB. One of the main proteins we talk about that regulate on a very high level is p53. It's even got a nickname: it's the "guardian of the genome." It's so important, actually, that Science Magazine called it, "the molecule of the year" in 1993. Theobromine, the main molecule that's in chocolate, hasn't even gotten this honor yet. So it shows you how important p53 is. It's more important than chocolate. P53 will bind DNA directly to produce proteins that block the progression of the cell cycle. One of those proteins include p21. P21 will function to inhibit CDK. So the CDK will not be able to activate DNA replication or activate mitosis. RB is another protein that is associated with the function of P53, and these proteins are considered tumor suppressor genes, so RB is a protein that is produced from a tumor suppressor gene, just like p53, so I'll write that down here. These proteins are considered tumor suppressor genes... They're made from tumor suppressor genes I should rather say. These proteins are made from tumor suppressor genes, which are important to have because if they are defected, or if they have a mutation in them that makes them have loss of function, so that's an important term, (repeats) defected or if they have a loss of function, what ends up happening is that you tend to get cancer. Cancer, which I think you and I can both agree is not a good thing to have. So, it is very important to have tumor suppressor genes. To illustrate how important that is, if you look at p53, greater than 50% of tumors have a defect in p53. RB got its name because a defect in RB would lead to a tumor of the eye, known as retino-that's where you got the R- retinoblastoma, which is why these two proteins are considered tumor suppressor genes. P21 is very unusual in that it doesn't actually lead to cancer when it's defected. Instead, scientists have found that mice that are without p21 have the ability to regenerate their limbs. How weird is that?! P21 lack causes the ability to regenerate their limbs, their arms and legs. So we're all still trying to figure out exactly how some of these key proteins work. But it's important to understand that these tumor suppressor genes are essential for making sure that we regulate the cell cycle so we don't just go to the divide, divide, divide phase. We want to make sure that we only divide when it's appropriate, when a cell is ready to, or if it's even a cell that is supposed to divide in the first place. Because, as we'll see in our next couple of videos, mitosis, or cell division, requires a lot of energy and protein machinery to happen. So we need to make sure it's the right time to divide.