The Cell Cycle

The cell cycle is a recurring sequence of events that extends from the time of a cell's formation until its division is completed.

Interphase: The control of cell division resides in the subphases of interphase.

1. During Gl, cells assemble most of the carbohydrates, lipids, and proteins that are needed by the cell and for export.
2. During the S phase the DNA and histones are copied.
3. During G2, further protein synthesis drives the cell toward mitosis.

Most of a cell's existence (about 90%) is spent in interphase. Mitosis occupies only a small portion of the cell cycle.

• During interphase the cell's mass increases, the cytoplasmic components approximately double in number, and the DNA is doubled.
• Some cells are arrested in interphase and usually never divide again (example: brain cells).

This animation of the Cell Cycle from Cells Cycle has a little audio but it's not important for understanding the animation. You do not need to leave the Cell Cycle page.

This animation (Audio - Important) describes the cell cycle.

Mitosis Has Four Stages:

• prophase,
• metaphase,
• anaphase, and
• telophase.

Chromosomes are moved by a spindle apparatus composed of two sets of microtubules that extend from each pole (centriole) of the cell and overlap at the equator.

Prophase - The Beginning of Mitosis:

1. Chromosomes (already duplicated during interphase) become visible as rodlike units, each consisting of two sister chromatids joined at the centromere.
2. The nuclear membrane breaks up and the spindle forms.
3. Microtubules move one pair of centrioles to opposite poles of the cell.

The Transition from Prophase to Metaphase:

1. Sister chromatids become oriented toward opposite poles.
2. When all the chromosomes are aligned at the cell's equator halfway between the poles, the cell is said to be in metaphase.

From Anaphase Through Telophase:

1. Sister chromatids separate and move toward opposite poles.
2. Now each chromatid is an independent daughter chromosome.
3. Telophase begins when chromosomes arrive at the poles.
4. The nuclear envelope forms from the fusion of small vesicles and mitosis is complete.

At the conclusion of mitosis, each new cell has the same chromosome number as the parent nucleus.

This page from Cells Alive has a good animation of Mitosis and a video of a cell dividing. You do not need to leave the page.

This animation (Audio - Important) describes the stages of mitosis.

This animation (Audio - Important) is a little quiz on the stages of mitosis.

REVIEW: DNA replication occurs
Answer between the gap phases of interphase.