Page 58 - Demo 1

MALFUNCTIONS OF THE CELL CYCLE

Some cells have the capacity to divide throughout their life cycle, while
others stop dividing at adulthood. Skin cells, for example, divide constantly to
replace dead cells that are sloughed off the surface of the body. In the same
way, cells in the bone marrow connually move through the cell cycle and
produce about two million red blood cells each second.

Other cells, including many cells in the nervous system, leave the cell
cycle, enter a non-growing state or G0, and cease to divide in adulthood. It is
the ability to enter G0 that accounts for the differences in the lengths of the
cell cycle among various ssues. For example, epithelial cells of the digesve tract
divide more than twice daily to renew the lining of the gut. By contrast, liver
cells spend most of their me in G0 phase, dividing only once in one or two years.
Mature muscle cells and neurons do not normally leave G0.

When a cell undergoes mitosis, it creates two genecally idencal
daughter cells that carry a copy of the original cell's DNA. Errors in this process
result in incorrect DNA copies; and the effects of these errors on the health of
the organism range from benign to deadly, depending on their number of
errors and type. One potenal consequence is cancer – sciensts trace all cancer
types back to harmful mutaons mulplied by mitosis.

DNA is the genec blueprint that contains the hereditary material in
nearly all organisms. The improper copying of DNA produces errors, or
mutaons.

Cancer

Cancer is a genec disease caused by a lack of control in the cell cycle. It
affects many different cells and ssues in the body. Cancer occurs when
mutated cells ignore or override the normal "checkpoints" regulang mitosis
and begin to reproduce uncontrollably.

Cancer is characterized by two properes: (1) uncontrolled cell division
and (2) the ability of these cells to spread, or metastasize, to other sites in the
body. If a cell divides in an unregulated manner, it will form a noncancerous
growth called a benign tumor. A benign tumor can be removed by roune
surgery. If cells in the tumor acquire the ability to grow connuously and
metastasize, the tumor becomes cancerous, or malignant. A cell becomes
cancerous if it accumulates a number of specific mutaons over a period of me,
thus, most cancers are age-related.

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