Over time, many of the cells that make up our bodies age, die and need to be replaced.
The process by which a cell reproduces to create two identical copies is known as mitosis.
Cells formed by mitosis are known as daughter cells.
The cell division process occurs as an orderly progression through four different stages, known collectively as the 'cell cycle'.
Many of the abnormal traits of cancer cells are due to defects in genes that control cell division.
The Cell Cycle
The cell cycle consists of four stages: G1, S, G2, and M.
G1 and G2 are 'gap' phases in which the cell grows and prepares to divide.
S in the synthesis phase in which the chromosomes (DNA) are copied (replicated).
M is the mitotic phase in which the cell physically divides into two daughter cells.
Most cells are NOT actively dividing. These cells are in a resting state (G).
Mitosis (M phase)
Mitosis in normal cells produces two cells with identical genetic content.
Mitosis has four sub-phases:
Prophase - Chromosomes condense, the nuclear membrane breaks down, and spindle fibers form
Metaphase - The replicated chromosomes line up in the middle of the cell
Anaphase - Chromosomes separate and the cell becomes elongated, with distinct ends (poles)
Telophase - Nuclear envelopes re-form at the two poles and new cell membranes are formed to create two independent cells
DNA Synthesis (S phase)
Humans have 46 chromosomes, 23 from each parent.
Each chromosome is comprised of a single piece of DNA containing millions of nucleotides.
A pair of homologous chromosomes has the same genes, but can have different versions of those genes.
In many cancer cells the number of chromosomes is altered so that there are either too many or too few chromosomes in the cells. These cells are said to be aneuploid.
Errors may occur during the DNA replication resulting in mutations and possibly the development of cancer.
Cells have mechanisms to correct errors due to faulty DNA replication.
Many chemotherapy agents target the S phase of the cell cycle.
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