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Main content
Current time:0:00Total duration:4:09
IST‑1 (EU)
IST‑1.D (LO)
IST‑1.D.1 (EK)
IST‑1.D.2 (EK)

Video transcript

now the cell cycle is not a sort of thing that occurs in a very unchecked manner there's actually a lot of regulation in play here in fact there are two key places that we have extensive regulation of the cell cycle the first checkpoint is right here between the g1 and the S phase so we regulate before we get to the point of DNA replication the other major checkpoint is right here between g2 and the step where we jump right to mitosis and there are a couple of proteins that regulate this process two main ones are called cyclin dependent kinase a--so cyclin dependent kinase --is which as you may recall a kinase is something that adds a phosphate group so I'll put in parentheses it'll plus a phosphate group and it'll add a phosphate group on other enzymes or proteins to either activate or inactivate them and these cyclin dependent kinases will work together with the protein you might be able to guess the name of cycling's alright because what else with these kinase is depend on so an important thing to notice is that these cyclin dependent kinases or CDKs are always present all the different types are always present in a Cell but their default form or their default function is for them to be inactive and so they need to be activated by these cyclin proteins and the point of regulation here is that specific cyclin s'alright specific with respect so specific cycling's are made at specific times and again the reason why they're both so important is that when you have a cyclin dependent kinase it is only active when they are bound to a specific cyclin it's at this point again that this guy is active and the cdk is the business end of this complex so that's the reason ing one you'll see the production of cycling's D and cyclin e and from there you'll see cdk2 bound to your cyclin e and at the same time you'll also have your cdk4 bound to your cyclin d these activated kinase is then specifically the cdk4 cyclin D complex will phosphorylate a protein called RB so I'll draw just a little reaction over here where we add a phosphate group on our RB protein so when RB is phosphorylated it can't inhibit DNA replication like it usually is supposed to do the phosphate group renders it inactive and this is sort of the setup we have as we go further on in our cell cycle in the S phase we have cycle and a produced cyclin a will complex again with cdk2 most directly to activate DNA replication so it helps to activate DNA replication and in a similar way we have cyclin b only produced in the g2 phase because the cyclin b cdk1 complex is able to activate activate what step do you think mitosis or cell division so it's important to recognize that in order to pass these checkpoints you need to have these cyclin proteins present so that they can go ahead and inhibit proteins that are blocking DNA synthesis or replication from occurring or so they can promote the production of proteins that are needed for mitosis
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