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Mitosis study guide
Chapter 10
10-2
Vocab: centromere, centrosome, chromosome, chromatid, centriole, spindle,
(all phases of cell cycle and mitosis listed below), replicate, cancer.
Onion root tip lab.
A cell goes through many cell cycles growing, preparing to divide, and
producing identical daughter cells, until it dies. DNA controls the cell’s rate of
division and the time of the cell’s death. Some cells, such as red blood cells,
cannot divide once they become mature. Other cells divide and last a few
days to a few years. Some abnormal cells divide too fast or do not die when
they should, which may cause cancer in animals. The study of mitosis and
the cell cycle helps us understand how to cure cancer and even how to
reverse the effects of age and disease.
During the cell cycle, a cell grows, prepares for division, and divides to form
two identical daughter cells. The cell then begins the cycle again.
The cell cycle is divided into interphase (growth and preparation for division),
and M phase (cell division). Interphase lasts the longest. During interphase,
the cell first grows and multiplies organelles during the G1 phase. During the
S (synthesis) phase of the cell cycle, chromosomes replicate ready for cell
division. As a result, the chromosomes form two identical sister chromatids
joined by a centromere. The last stage of interphase is G2 when organelles
get ready for cell division.
M phase includes mitosis and cytokinesis. Mitosis is the division of the cell
nucleus into two identical parts. This takes much less time than interphase.
1. Prophase is the first stage of mitosis. During prophase in animal cells,
the centrioles separate and take up positions on opposite sides of the
nucleus. In addition, chromosomes condense and the spindle appears.
2. During metaphase, the chromosomes line up across the center of the
cell. The chromosomes are connected to the spindle by star-like
microtubules.
3. During anaphase, the centromeres that join the sister chromatids split,
and the sister chromatids separate and become individual
chromosomes. This way, identical DNA sisters are sent to each end of
the cell.
4. In telophase, the chromosomes, which were distinct and condensed,
uncoil and disperse as the nuclear envelope re-forms. This is the last
stage of mitosis.
Cytokinesis is the division of the cytoplasm into two cells. This is technically
not part of mitosis. It may occur simultaneously to telophase. In animals, the
cell membrane pinches in the center to make two cells. In plants, a thin
membrane called a cell plate forms to separate the cells, and a cell wall
grows on it to separate each new daughter cell.
The cell cycle is carefully regulated by the cell’s DNA. Cancer occurs when
cells grow and divide uncontrollably. These cancer cells eventually form
growths called tumors. Tumors can cause medical problems when they
spread through the body. Sometimes cancer is caused by a genetic mutation
that allows the cell to divide even when chromosomes are incorrectly
replicated. By understanding the cell cycle, we have learned to help many
cancer patients to lead normal lives again.