BIO152H5 Chapter Notes - Chapter 12: Sister Chromatids, Cell Cycle, Cell Division
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Chapter 12 Review
• Unicellular organisms reproduce by cell division; multicellular organisms depend on cell division for
their development from a fertilized egg and for growth and repair. Cell division is part of the cell cycle, an
ordered sequence of events in the life of a cell from its origin until it divides into daughter cells.
Most cell division results in genetically identical daughter cells (pp. 244–246)
• The genetic material (DNA) of a cell—its genome—is partitioned among chromosomes. Each
eukaryotic chromosome consists of one DNA molecule associated with many proteins that
maintain chromosome structure and help control the activity of genes. Together, the complex of DNA and
associated proteins is called chromatin. The chromatin of a chromosome exists in different states of
condensation at different times. In animals, gametes have one set of chromosomes and somatic
cells have two sets.
• Cells replicate their genetic material before they divide, each daughter cell receiving a copy of the DNA.
Prior to cell division, chromosomes are duplicated. Each one then consists of two identical sister
chromatids joined along their lengths by sister chromatid cohesion and held most tightly together at a
constricted region at the centromeres of the chromatids. When this cohesion is broken, the chromatids
separate during cell division, becoming the chromosomes of the new daughter cells. Eukaryotic cell
division consists of mitosis (division of the nucleus) and cytokinesis(division of the cytoplasm).
The mitotic phase alternates with interphase in the cell cycle (pp. 246–253)
• Between divisions, a cell is in interphase: the G1, S, and G2 phases. The cell grows throughout interphase,
with DNA being replicated only during the synthesis (S) phase. Mitosis and cytokinesis make up
the mitotic (M) phase of the cell cycle.
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