CISN - Cancer Research - The Cell Cycle

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The Cell Cycle

The Cell Cycle:
The Circle of Life!

The study of genetics and the study of how cells work are closely related. The process of passing genetic information from one generation to another depends completely on how cells grow and divide. To better understand research, it is important to know a little bit about the cell cycle and a few of the key factors that can affect this.

Definition:

The cell cycle is a critical process of defined steps that a cell undergoes in order to copy itself exactly.

Characteristics of Cells:

  1. Normal cell division is required for the generation of new cells during development and for the replacement of old cells as they die.

  2. “There are checkpoints that exist at each phase in the cell division process. At the checkpoint, the cell checks itself over to make sure it’s OK before it moves on to the next phase. If it’s not OK, it can’t go on.

The cell does this to protect you from mutations. Think about it, you are making over a billion cells every day in your blood system. As each cell goes through the cell division process there are signals that tell it to proceed. Those are called growth inducers. They tell the cell, “Let’s go. Keep moving.”. And then there are other signals that tell the cell to stop. Those are growth inhibitors.

So, basically, it’s a process of one, stop and check; two, make sure everything is OK; and, three, let those cells that look OK proceed.”
- Quote from Scientists on Science, AACR

The Cell Phases

Image courtesy of herb4cancer
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This illustration of the cell cycle shows the many built-in pathways to correct cell replication mistakes that may eventually lead to mutations. The body is truly remarkable in it’s ability to maintain health.

Step 1:

Interphase is the part of the cell cycle during which the cell grows, copies its DNA, and prepares to divide. Interphase is usually divided into three stages:

  • G1 Phase - Cells increase in size. The G1 checkpoint control mechanism ensures that everything is ready for DNA synthesis (replication).

  • S (synthesis) Phase – DNA replication (copying DNA) occurs during this phase.

  • G2 Phase – During the gap between DNA synthesis and mitosis (cell division), the cell will continue to grow accumulating nutrients for the work of mitosis. The G2 checkpoint control mechanism ensures that everything is ready to enter the next phase in the cell cycle.

Step 2:

In the cell cycle, Mitosis (M phase) is the process of dividing up the newly copied chromosomes to make certain that the new cells each get a full set.

  • M Phase - Cell growth stops at this stage and cellular energy is focused on the orderly division into two daughter cells. A checkpoint in the middle of mitosis (Metaphase Checkpoint) ensures that the cell is ready to complete cell division.

Step 3:

When mitosis is complete and new nuclei have formed, the cell divides into two smaller identical cells. The new cells are ready to begin the cell cycle again.

CISN Summary:

  1. Cells are the building blocks of all living creatures. Creation and maintenance of any cellular organism requires a delicate balance between:
    • Cell growth (proliferation), cell division (differentiation) and cell death (apoptosis).
    • Signals that regulate the cell’s cycle of growth and division.

  2. Elaborate control systems exist to regulate and coordinate these essential processes. Cancer is the most devastating consequence of loss of control of these processes.

  3. Most cancers arise from a single cell that has undergone a growth-promoting mutation. Over time, the “children” of this original cell acquire additional mutations and the tumor becomes malignant through a natural selection process that favors the most rapidly dividing and aggressive cells.
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