Cell Division Section: 2.5

Growth and repair of cells occurs in a process called mitosis.

In interphase, the cell grows to its mature size, makes a copy of its DNA, and prepares to divide into two cells. Chromatin

During prophase, the threadlike chromatin in the cell’s nucleus begins to condense and coil, like fishing line wrapping around a ball. Scientists call each doubled rod of condensed chromatin a chromosome. The nuclear membrane dissolves. Chromosomes Centrioles

In metaphase, the chromosomes move to the middle of the cell and line up along the equator. Centriole Spindle fibers Chromosomes

In anaphase, the spindle fibers begin to "reel in" the chromosomes to opposite ends of the cell, pulling them apart. Chromosomes Centriole Spindle fibers

In telophase, two nuclei form around the chromatids at the two ends of the cell. Nuclear Membrane reforming Chromatin

During cytokinesis, the cytoplasm divides, distributing the organelles into each of the two new cells. Chromatin

A DNA molecule looks like a twisted ladder, or spiral staircase. Because of its shape, a DNA molecule is often called a “double helix.”

The two sides of the DNA ladder are made up of sugar and phosphates. Each rung is made up of two nitrogen bases.

There are four kinds of nitrogen bases: adenine (A), thymine (T), guanine (G), and cytosine (C). Adenine (A) only pairs with thymine (T), while guanine (G) only pairs with cytosine (C).