| BACK |
| HOME |
|
| NEXT |
|
|
|
|
|
|
| 25 years ago, at about this time of year, while anxious over finishing my Ph.D, I found out that I had cancer and it would take three weeks for the specialists at Dana Farber to see me. While I had time on my hands I learned about cancer. While we are waiting for the time that I will describe the staging and treatment of my cancer, allow me to give a description of cancer and its treatment in a greatly over-simplified form. I hope you find it informative, and will help you to understand how chemotherapy works as I describe it later. Cell biology is the farthest from my training so I relied heavily on Wikipedia's entry on cell cycle. |
| CANCER IN A NUTSHELL - PART THREE THE CELL CYCLE EMPHASIZING THE ROLE OF DNA |
| One of the purposes of DNA is to bring about the division of a cell into two daughter cells. This is how tissues grow or are renewed. It is also how cells mature. With each division, a cell becomes more differentiated (this means more specialized). In this way, a single cell can become all the various types of cells of an organism. This process from a new cell through growth to division takes place in distinct stages called the cell cycle. Certain chemotherapy drugs are more effective during specific stages of the cycle. Other drugs are effective in any stage of the cell cycle. |
| The sequence of steps in the cell cycle are known by an abbreviation shown in parentheses. The steps in order are: Gap 1 (G1), Synthesis (S), Gap 2 (G2), and Mitosis (M). In each of these stages there is biological activity progressing the cell toward replication. There is also a resting state where the cell is not actively preparing for cell division. The resting state is called Gap 0 (G0). If a drug is only active during the cell cycle, cells in G0 are not as vulnerable to the chemotherapy treatment. Also, the length of time a cell is in each stage varies from cell to cell type. |
| Each of the steps in the cell cycle will be briefly described. |
| G1 - The new cell grows, takes in nutrients, synthesizes all the proteins that it needs to do its specific functions, and all the proteins needed to synthesize DNA. |
| S - The DNA is synthesized. During this stage the DNA divides into single strands and the complimentary base pairs are added to create a duplicate double helix. The cell is especially vulnerable during this stage because during the synthesis of DNA wrong molecules may substitute, the DNA is subject to shape deformation, and drugs are more likely to damage the DNA. |
| G2 - After DNA has been synthesized, a large number of specialized molecules that are needed for mitosis are synthesized. One very important protein structures made at this time are the microtubules. Microtubules are the spindle like structures that are used to draw the chromosomes to opposite sides of the cell during mitosis. They are a target of certain chemotherapy agents. |
| M - Mitosis is a multistage process whereby the cell splits in half its genetic material and cleaves into two separate identical cells. Mitosis is quite complicated, so I will give a simplified summary. Two focusing points called centrosomes serve as anchors for the microtubules migrate to opposite sides of the cell. Meanwhile the nucleus boundary (membrane) breaks up and the genetic material assisted by proteins aligns at the center of the cell in chromosomes (remember the chromosomes are the containers for DNA). The microtubules attach to the chromosomes. The microtubules shorten and draw the two groups of chromosomes to opposite sides of the cell. A new nuclear membrane forms around each newly separated set of chromosomes. Shortly after this, the cellular material is divided up and the cell divides. |
| The cycle starts all over again. |
| Cells that are actively dividing are most susceptible to chemotherapy agents. Such cells include tumor cells, actively growing cells (such as a young child's organs), and cells that are in constant regeneration (such as skin, hair, mucous membranes, GUI tract blood cells, and sex cells). |
| Next up the general principles of chemotherapy and back to the narrative. |
| Stay tuned for more of the story. |
| (Cancer Chronicles is a series of status updates that account the events of 25 years ago when I went through a bout with cancer. Its purposes are multi-fold: catharsis, education, information, celebration, etc. ) |
| This originally was posted to facebook October 8, 2012. |
|
|
|
|
|