Checkpoints work as breaks in the cell cycle, allowing for a multi-step control of the cycle's stages. Mutations in the breaks allows for cell pathways to activate without signals, like a car accelerating without breaks.
In order for the cell replication process to be successful, the DNA code must be uncompromised and DNA checks must occur. DNA must be stable, functional, and must be able to be replicated for the cell cycle to progress.
In S phase, DNA is replicated and histone proteins are created (to wrap DNA around). In G2 phase, the cell starts to split and DNA segregates.
Cells that are specially differentiated stay in the G0 or quiescence-phase. Here, cells like neurons and red blood cells serve specific tasks and do not need to replicate. However, they can be reverted back to a normal G1 stage when given proper signaling. If damaged, they simply enter apoptosis from G0.
CDKs or Cycline dependent kinases are essential in cell cycle control. Kinases transfer phosphate groups from ATP to proteins in a pathway in order to cause an activating change in conformation. Kinases activate proteins, by phosphorylating them.
Post-translational modifications are changes made to a protein's structure after it was originally created by ribosomes in the ER. These changes can involve Phosphorylation or dephosphorylation, ubiquitination, methylation, or the addition of functional groups or structural changes made that alter the protein's structure/function.
3 classes of CDKS: 1) G1/S CDKs bind and cause DNA replication 2) S phase CDKs are essential in regulating DNA replication 3) Mitose-cyclins promote and drive mitosis.
Rb is a protein that when mutated, causes tumor formation in the eye (retinoblastoma). Rb is an inhibitor of the cell cycle progression. Without a functional Rb, the cell will not be able stop itself from replicating.
p53 is a cell cycle checkpoint. They halt the cell cycle if they detect DNA damage. External factors such as UV rays can cause DNA mutations, but also mistakes in replication or segregation can also cause DNA damage. Damage can be fixed using specific proteins but p53 stops the cell cycle and allows for DNA damage control.
Mutations in p53 can allow a cell with DNA damage to successfully replicate. This can result in cells that are missing DNA segments or are damaged in some way. In many cases, this can lead to cells that are cancerous in nature because they can replicate continuously despite having DNA damage.