Cell Cycle
Objectives
- Students will be able to label the parts of the cell cycle and describe what happens in each phase.
- Students will understand and explain chromosome structure.
Why do Cells Divide?
The process of cell division is responsible for carrying out three functions essential to life. These are:
- Reproduction
- Growth and development and
- Cell renewal and repair
Reproduction
In many single-celled organisms, such as prokaryotes, simple cell division involves binary fission, reproduction that "divides in half" the cell (organism), replicating itself precisely. This is the major, and sometimes, the only form of reproduction. Here, the new, genetically identical organisms ("daughter" cells) are produced from a single parent cell. This is referred to as asexual reproduction, reproduction that occurs without sex.
Growth and Development
Sexually reproducing multicellular organisms begin as a single fertilized egg, or zygote, but an adult organism may have trillions of cells, with those cells dividing at most every second. Cell division enables multicellular organisms to grow to adult size, doubling the cell number with each division. In the human body, for example, about 10 trillion cell divisions occur during a lifetime.
Cell Renewal and Repair
During its lifetime, an organism's cells continually wear out and need to be replaced. Other cells suffer injury and disease. It is essential that these cells be replaced by cells identical to the original ones, in order to maintain their functions - this is accomplished by the process of cell division.
Each of these functions: Reproduction, Growth and Development, and Cell Repair and Replacement - all are carried out in a carefully timed and regulated cell cycle. A single cell cycle includes all cell events that occur from the cell's formation until it is ready to divide into two cells. As soon as it divides, the daughter cells each undergo their own cell cycles, so the process is continuous. For the functions of cell division to be carried out with precision, the complete set of genetic information within each cell must be copied exactly and a complete copy of it passed to each new cell. Most importantly, cell division must be carefully timed and regulated, allowing the right kinds of cells to be reproduced in exactly the right numbers. A breakdown of the molecular control of cell division results in the disease called "cancer," cells reproduce randomly and rapidly and cause the production of tumors.
