Chapter 9 - The Cell Cycle
The continuity of life is based on the reproduction of cells, or cell division.
Cell division plays several important roles in life. The division of one prokaryotic cell reproduces an entire
organism. The same is true of a unicellular eukaryote. Cell division also enables multicellular eukaryotes to
develop from a single cell.
The cell division process is an integral part of the cell cycle, the life of a cell from the time it is first formed
from a dividing parent cell until its own division into two daughter cells. Passing identical genetic material to
cellular offspring is a crucial function of cell division.
9.1 Most cell division results in genetically identical daughter cells
A cell's endowment of DNA, its genetic information, is called its genome.
A typical human cell has about 2m of SNA, a length about 250,000 times greater than a cell's diameter.
The replication and distribution of so much DNA are manageable because the DNA molecules are packaged
into structures called chromosomes, so named because they take up certain dyes used in microscopy.
Each eukaryotic chromosome consists of one very long, linear DNA molecule associated with many proteins.
The DNA molecule carries several hundred to a few thousand genes, the units of information that specify an
organism's inherited traits. The associated proteins maintain the structure of the chromosome and help
control the activity of the genes.
Together, the entire complex of DNA and proteins that is the building material of chromosomes is referred to
as chromatin.
The nuclei of human somatic cells, all body cells, each contain 46 chromosomes, made up of two sets of 23,
one set inherited from each parent.
Reproductive cells, or gametes, have half as many chromosomes as somatic cells. One set of 23
chromosomes for human.
Each duplicated chromosome has two sister chromatids, which are joined copies of the original
chromosome. The two chromatids, each containing an identical DNA molecule, are initially attached all along
their lengths by protein complexes called cohensins; this attachment is known as sister chromatid cohension.
Each sister chromatid has a centromere, a region containing specific DNA sequences where the chromatid is
attached most closely to its sister chromatid. This attachment is mediated by proteins bound to the
centromeric DNA sequences and gives the
condensed, duplicated chromosome a narrow
waist.
Later in the cell division process, the two sister
chromatids of each duplicated chromosome
separate and move into two new nuclei, one
forming at each end of the cell. Once the sister
chromatids separate, they can no longer called
sister chromatids but are considered individual
chromosomes. Thus, each new nucleus receives
a collection of chromosomes identical to that of
the parent cell.
Mitosis, the division of the genetic material in
the nucleus, is usually followed immediately by
cytokinesis, the division of the cytoplasm.
Mitosis and cytokinesis produced the 200 trillion
somatic cells that now make up your body and
the same processes continue to generate new
cells to replace dead and damaged ones.
9.2 The mitotic phase alternates with interphase in
the cell cycle
The continuity of life is based on the reproduction of cells, or cell division.
Cell division plays several important roles in life. The division of one prokaryotic cell reproduces an entire
organism. The same is true of a unicellular eukaryote. Cell division also enables multicellular eukaryotes to
develop from a single cell.
The cell division process is an integral part of the cell cycle, the life of a cell from the time it is first formed
from a dividing parent cell until its own division into two daughter cells. Passing identical genetic material to
cellular offspring is a crucial function of cell division.
9.1 Most cell division results in genetically identical daughter cells
A cell's endowment of DNA, its genetic information, is called its genome.
A typical human cell has about 2m of SNA, a length about 250,000 times greater than a cell's diameter.
The replication and distribution of so much DNA are manageable because the DNA molecules are packaged
into structures called chromosomes, so named because they take up certain dyes used in microscopy.
Each eukaryotic chromosome consists of one very long, linear DNA molecule associated with many proteins.
The DNA molecule carries several hundred to a few thousand genes, the units of information that specify an
organism's inherited traits. The associated proteins maintain the structure of the chromosome and help
control the activity of the genes.
Together, the entire complex of DNA and proteins that is the building material of chromosomes is referred to
as chromatin.
The nuclei of human somatic cells, all body cells, each contain 46 chromosomes, made up of two sets of 23,
one set inherited from each parent.
Reproductive cells, or gametes, have half as many chromosomes as somatic cells. One set of 23
chromosomes for human.
Each duplicated chromosome has two sister chromatids, which are joined copies of the original
chromosome. The two chromatids, each containing an identical DNA molecule, are initially attached all along
their lengths by protein complexes called cohensins; this attachment is known as sister chromatid cohension.
Each sister chromatid has a centromere, a region containing specific DNA sequences where the chromatid is
attached most closely to its sister chromatid. This attachment is mediated by proteins bound to the
centromeric DNA sequences and gives the
condensed, duplicated chromosome a narrow
waist.
Later in the cell division process, the two sister
chromatids of each duplicated chromosome
separate and move into two new nuclei, one
forming at each end of the cell. Once the sister
chromatids separate, they can no longer called
sister chromatids but are considered individual
chromosomes. Thus, each new nucleus receives
a collection of chromosomes identical to that of
the parent cell.
Mitosis, the division of the genetic material in
the nucleus, is usually followed immediately by
cytokinesis, the division of the cytoplasm.
Mitosis and cytokinesis produced the 200 trillion
somatic cells that now make up your body and
the same processes continue to generate new
cells to replace dead and damaged ones.
9.2 The mitotic phase alternates with interphase in
the cell cycle
