What is Cancer?
Technically speaking, cancer is over-active cell division, which creates more new cells than the body needs. More generally, when cells divide and increase at a rate faster than cell death, they collect in the body, forming a tumor.
You may ask, "If cells are dividing, aren't they getting smaller? If so, why is over-active cell division a problem?" BUT, cell division is the process your body goes through in order to duplicate cells. Normally, duplicates are only made to replace old cells, or to repair a spot in your body that is injured and needs replacement cells fast.
In order to divide and result in two identical cells, the original cell must first replicate all of its organelles, proteins, and DNA so that an identical set of these cellular components can be put into the new (daughter) cell.
REMEMBER: DNA provides the instructions for the development and functioning of all cells. If the DNA does not replicate or divide successfully, it could lead to cell abnormalities and possibly cell death.
Below is a general review of the NORMAL cell cycle and cell division in human cells:
Cell Cycle (Interphase):
- G1 Phase: "Growth Phase" during which cell grows to prepare for DNA replication
- S Phase: "Synthesis Phase" during which all DNA is replicated and each chromosome has 2 sister chromatids
- G2 Phase: "Second Growth Phase" during which cell makes proteins and other cellular components necessary for cell division
After Interphase, the cell goes through Mitosis, or M Phase, during which the cell divides, resulting in two identical cells
Steps of Mitosis: PMAT
In the following images, blue represents chromatin, green is microtubules, and pink is kinetochores. Explanations of these proteins are provided on the proteins page.
Prophase: During prophase, the genetic material condenses into two identical chromosomes, centrosomes (that produce and organize microtubules) form and move to opposite ends of the cell, and the nuclear envelope begins to degrade. Centrosomes are denoted by the dense regions of green at either pole of the cell.
Metaphase: During metaphase, the chromosomes align along the equator of the cell, microtubules from the centrioles attach to each chromosome at the kinetochore (a protein structure on the chromosome where microtubules attach), and the cell prepares to stretch into 2 distinct cells.
Anaphase: During anaphase, the chromosomes split and one sister chromatid of each chromosome is pulled to each pole by microtubules attached to the centriole. As microtubules contract, spindle fibers extend along the length of the dividing cell to push the two individual cells closer to division.
Telophase: During telophase the two daughter cells become distinct from each other because the nuclear envelope is re-formed in each of the cells and chromosomes de-condense into loose chromatin. This "rebuilding" of the daughter cells occurs simultaneously with Cytokinesis, which is the last process of division in the creation of two daughter cells.
The cell cycle is performed and controlled by many different proteins, such as microtubules, centrosomes, and kinetochores. Through the study of cancer, scientists can discover what proteins cause over-active cell division, learn about how the protein functions in the cell, and manipulate it to see they can change the protein's role in the cell.
See the Cell Cycle in Action!
Now, imagine the cell cycle in a cancerous cell. Cancerous cell division occurs at a much faster rate!