Cell cycle



The cell cycle is an orderly series of steps that a cell passes through to duplicate its genetic material and split into two new cells. The model of this process is often drawn as a circle (pictured at right).

Although largely thought of as consisting of mitosis (or division) and interphase, the entire process consists of 4 distinct phases. The Gap1 (G1) and Gap2 (G2) stages are separated by the S (DNA synthesis) and M (mitosis) phases, respectively. Each previous phase needs to be completed before the next phase can start.

Mitosis


Mitosis is the process of cell division that produces two daughter cells from one single parent cell. The daughter cells are the same with each other and the original parent cell.

Mitosis included four stages: Prophase, Metaphase, Anaphase, and Telophase.

Prophase: Prophase is a period that condenses the chromatin into chromosomes. every single chromosome has two sister chromatids, they were copied from the chromosome. At the end of this period the nuclear envelope breaks down into vesicles.

Metaphase: Metaphase has included two periods: prometaphase and metaphase. Prometaphase is the period between prophase and metaphase. During prometaphase the nuclear envelope breaks up, spindle moves to the center of the cell, and the kinetochore attaches to the kinetochore fibers. When it linked the chromosomes and could control the movement of it, then the kinetochores will try to attach the polar fibers.

In metaphase the kinetochores are moves facing the pole and it will moves the chromosomes into the center of the spindle and let them facing each other.

Anaphase: Anaphase is a stage in both mitosis and meiosis that chromosomes moves to poles of the cell.

Telophase: Telophase is a period wherein the chromosomes arrive at the poles, the microtubules disappear and the nuclear envelope forms. Then following the separation of the cytoplasm (cytokinesis), the cell membrane pinches in to divides the cells in two. 

Gap 1
Gap 1 is the period that between the end of mitosis and the beginning of DNA synthesis. During this period Cdk, RB, and Cyclin were found in it.

DNA Synthesis (S)
They copide the DNA Synthesis to produce the two daughter cells in this period. These chromosomes are separated during mitosis. 

Gap 2
Gap 2 seems like the last period of the cell cycle, because it's happened after DNA synthesis and before the mitosis.

During this period the cell will keep growing and producing new proteins. And at the end of this period it will proceed to the next period, the mitosis period.

Cyclin - dependent kinase
Cyclin-dependent kinase, which was also called Cdk, was an very important thing that only dependent on it can finish the transitions from G1 to S and G2 to Metaphase.

By catalyzing the phosphorylation of certain target proteins, Cdk's play important roles in initiating the steps of the cell cycle.

Cyclin
All the periods in the cell cycle needs cyclin. Cyclin have different concentrations, and in the cell cycle it will be changed to cooperated in the four periods.

When the concentration of the cell are low, the cyclin separated from the Cdk, inhibiting the enzyme's activity, probably by causing a protein chain to block the enzymatic site.

Cyclin have a lot of types, they are: Cyclin D, Cyclin A, Cyclin B, and Cyclin E. These different cyclin's actives will make the Cdk to phosphorylate different substrates.

The Cyclin was discovered by Leland H. Hartwell, R. Timothy Hunt, and Paul M. Nurse. They won the Nobel Prize because their contribution of discovered cyclin and cyclin-dependent kinase, central molecules in the regulation of the cell cycle. 

Retinoblastoma protein (RB)
Because the retinoblastoma protein was in the cell cycle, so it will prevent the damage copied DNA through the process by preventing its progression through the cell cycle into its DNA synthesis.

The retinoblastoma protein was also called pRb or Rb, the 'p' in pRb was stand for protein, this was also a way to be separated form the Rb gene.

pRb belongs to the Pocket protein family, it has a pocket that can bind proteins.

Cancer


If there is only one damaged gene that is responsible for the regulation of the cell cycle it may result in cancer. Genes which cause cancer when rendered dysfunctional by mutations are called oncogenes. Cells that do not respond to negative control over the cell cycle progression will keep growing in an unregulated manner and end up producing a tumor.

Malignant tumors can lead to death. When the malignant tumors do not get medicinal control it will grow to the secondary tumors. The secondary tumors will not only keep growing in the same place, but also change the location grown other tumors in the other location, and the benign tumors only growing in the same location.

The cellular oncogene of the normal cellular counterpart are called protooncogenes.

External Link
Here is a game that will help you to understand the control of the cell cycle.