Cell Cycle Regulation and Cancer

What is the cell cycle? 
The cycle that a cell goes through that leads to the cells replication.

What are the phases of cell regulation?   
  • G1 phase ... cells grow
  • S phase...genome replication
  • G2 phase...prepare for division
  • M phase...cells divide(mitosis)
  • C phase...cell division occurs( cytokinesis)

What are three main checkpoints for Cell regulation?
One is the  G2 checkpoint:
This checkpoint involve two proteins: Cyclins and CDK a.k.a Cyclin dependent Kinase. These two proteins are dependent on each other since CDK needs cyclins to function. 

are proteins that participate in the phosphorylation  of other proteins. 

During this phase CDK's accumulate cyclins( also called Mitotic cyclins)
which eventually bind to the CDK's to form complexes called MPF( also called Mitosis promoting Factor). 
After there is enough MPF the cell moves on to the next phase However MPF must be shut down before moving on to M phase( mitosis level). If it is not shut down then once in the M phase the cells will divide uncontrollably causing Cancer.

Second checkpoint is M checkpoint:

What is one function of MPF? 

MPF activates proteins that destroy cyclins (mitotic cyclins). The proteins that MPF activates are called Cyclin degrading proteins which eat up the cyclins thus leaving behind mostly CDK's and less MPF(*since cyclins were removed). After this happens Mitosis ends and moves on to the next checkpoint.

Third checkpoint is G1:
The phase where cells grow is reached. G1 cyclins bind to CDK's again and progress to the next level by releasing Cyclin degrading proteins which break down the G1 cyclin  telling the cell to move on to its next phase.

Cell regulation does not always work properly.

Tumor suppressor Genes:
will try to suppress the uncontrollable division( tumor)

What is the difference between tumor suppressor genes and tumor suppressor proteins?

Tumor suppressor proteins decide whether the cell will die or live and the genes that encode for the tumor suppressor proteins are tumor suppressor genes .

Which are some examples of Tumor suppressor Genes?
  • p53
  • pRB
  • pten
  • p27( breast cancer)
This is a protein that basically controls everything inside the cell.
This protein can get activated by proteins like ATM. When ATM senses something wrong within the cell like mutation in the cell's dna by radiation, what P53 will try to do is activate other proteins like SOS, NER, or BER to try and repair the damage. But, if the damage is too advanced and cannot be repaired then P53 will turn on the APOPTOSIS pathway in which the cell will die.

All these Tumor suppressor genes, will try to suppress tumors and will try to flourish conditions within the cell. PRB allows cell to grow and without this gene the cell wouldn't be able to grow so as a result the cell is not able to move on from G1 phase to S phase. If one tumor suppressor gene isn't successful because of mutations or others forms of damage, it can affect the cell in many ways. Because the gene isn't able to suppress the tumor, the tumor starts to grow bigger and bigger leading to cancer.

The uncontrollable growth of cell leading to tumors that interfere with the functions of the body. 
Ex. Lung cancer : tumors in the lungs that prevents one from breathing thus leading to death.

Tumor is a clump of cells that will not stop dividing: 
Cancer can spread to various parts of the body. This process is called (metastasis

What are the different types of tumors? 
  • Benign( non cancerous)
  • Malignant( cancerous)