MitosisCell Division

The Cell Cycle

The regular sequence of growth and division that

cells undergo.

A pumpkin grows by size by increasing both the size and the number of

cells. A single cell divides, forming two cells. Then two cells divide, forming

four, and so on.

This type of cell division occurs in all living things.

Guide for ReadingWhat events take place during the three

stages of the cell cycle?

Stage 1:InterphaseThe period before cell

division occurs.

During interphase, the cell grows to its mature size, makes a copy of its DNA,

and prepares to divide into two cells.

GrowthThe first part of interphase:

The cell doubles in size and produces all the structures needed to carry out its functions.

DNA ReplicationThe next part of interphase:

The cell makes a copy of the DNA in its nucleus in a process called replication.

Preparation for DivisionOnce the cell’s DNA has replicated preparation for cell division begins. The cell produces structures that it will use to divide during the rest of the cell cycle. At the end of interphase, the

cell cycle is ready to divide.

Review Question The regular sequence of growth and division that cells undergo?

The first stage of the cell cycle?

Stage Two:Mitosis

The second stage of the cell cycle.The stage during which the cell’s nucleus divides into two

nuclei. During Mitosis, one copy of the DNA is distributed into each of the two daughter cells.

ChromosomeEach rod of condensed chromatin

ChromatidEach identical rod, or strand, of the chromosome. The two

strands are held together by a structure called a centromere.

Fou

r Parts o

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itosis

Pro

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Meta

phase

Anap

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Telo

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Mitosis:Prophase

The chromatin in the nucleus condenses to form chromosomes.

Structures called spindle fibers form a bridge

between the ends of the cell. The nuclear

membrane breaks down.

Mitosis:Metaphase

The chromosomes line up across the center of the cell. Each chromosome

attaches to a spindle fiber at its centromere, which still holds the chromatids

together.

Mitosis:Anaphase

The centromeres split. The two chromatids

separate. One chromatid moves along the spindle fiber to one end of the

cell. The other chromatid moves to the opposite end. The cell becomes

stretched out as the opposite ends pull apart.

Mitosis:Telophase

The chromosomes begin to stretch out and lose

their rodlike appearance. This occurs in the two

regions at the ends of the cell. A new nuclear

membrane forms around each region of chromosomes.

Stage 3:Cytokinesis

The final stage of mitosis.

During cytokinesis, the cytoplasm divides,

distributing the organelles into each of the two new

cells.

Each daughter cell has the same number of

chromosomes as the original parent cell. At the end of cytokinesis, each

cell enters interphase, and the cell cycle begins

again.