Download Module A: Unit 2, Lesson 1 – Mitosis

Module A: Unit 2, Lesson 1 – Mitosis
Why do cells divide?
• Cell division takes place for different reasons.
• Cell division is important for asexual reproduction, which involves only one
parent organism.
• Most growth in a multicellular organism happens because cell division produces
new cells.
• Cell division also produces cells for repair.
What happens to genetic material during cell division?
• The genetic material in cells is called DNA (deoxyribonucleic acid).
• In eukaryotic cells, DNA is found in the nucleus.
• A DNA molecule contains the information that determines the traits that a living
thing inherits and needs to live.
• During most of a cell’s life cycle, DNA is found in a mass of loose strands called
chromatin.
• Before cell division, DNA is duplicated.
• As cell division begins, the chromatin is compacted into visible structures called
chromosomes.
• A duplicated chromosome is made of two identical structures called chromatids.
What are the stages of the cell cycle?
 The life cycle of a eukaryotic cell, called the cell cycle, can be divided into three
stages: interphase, mitosis, and cytokinesis.
• Interphase is the stage in the cell cycle during which the cell is not dividing.
• The cell grows to about twice the size it was when it was first produced. It
produces various organelles and engages in normal life activities.
• Changes that occur during interphase prepare a cell for division.
• In eukaryotic cells, mitosis is the part of the cell cycle during which the nucleus
divides.
• Prokaryotes do not undergo mitosis because they do not have a nucleus.
• Mitosis results in two nuclei that are identical to the original nucleus.
• When mitosis is complete, the cell has two identical sets of chromosomes in two
separate nuclei.
• Cytokinesis is the division of the parent cell’s cytoplasm.
• Cytokinesis starts during the last step of mitosis and eventually forms two
complete cells.
• In cells that have a cell wall, a cell plate forms during cytokinesis. The cell plate
separates the cell into two new cells.
What are the phases of mitosis?
• There are four phases of mitosis: prophase, metaphase, anaphase, and telophase.
• By the end of the four phases, the cell will have two identical nuclei.
• In prophase, the chromatin in the nucleus condenses into chromosomes. The
membrane around the nucleus breaks down.
• In metaphase, the chromosomes line up in the middle of the cell.
• In anaphase, the chromatids of each chromosome are pulled to opposite sides of
the cell.
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In telophase, a new nuclear membrane forms around each group of chromosomes,
which become less condensed.
Cytokinesis begins during this phase.
After mitosis, cytokinesis results in two new cells, and the two new cells start the
cell cycle again.