Question

How do Cdk and Ddk kinases regulate DNA replication to once per cell cycle? Specifically, when in the cell cycle are these kinases active and when are they inactive, what do they target, and how does this keep origin firing to once per cell cycle ?

Answer 1

When cell reproduction takes place, mainly two types of separation processes takes place, namely mitosis and meiosis. In mitosis, the cell gets separated into two child cells, each containing the same genetic material as the parent. In meiosis, the chromosome measure is halved for the parent and four new child cells are created. These divisions require the involvement of two kinase processes namely, CDK and DDK. Here, CDK refers to cyclin-dependent kinases and DDK refers to Dbf4-dependent kinase.

Both of these kinase processes are needed for the genetic replication and perpetuation of the mitosis and the meiosis processes. For every cell reproduction cycle, DNA replication happens only once. DNA once replicated, cannot be replicated again until the cell divides further. CDK helps in the advancement of the cell cycle. CDK boosts the duplication of DNA in chromosomes, supported by DDK. The most common substrates of CDK are Sld2 and Sld3. Replication of DNA can occur from multiple sites. In a cell cycle, most likely there are three regulators which make sure that DNA is regulated with onset of correct phase, namely, CDK, cyclins and APC/C enzyme.

With each cell cycle, only a single chromosomal copy is created which keeps the origin firing to once per cell. The MCM2–7 head case happens to be the first target for Cdc7–Dbf4. In order for CDK to be completely activated, the protein called cyclin should bind to CDK and then another kinase must phosphorylate it. These regulators help to move forward the cell cycle to the next phase. If the regulators in picture are not able to complete the requirements, the cell cycle might get terminated.