The Cell Cycle
The cell cycle includes the process in which single cells divide to
form TWO identical cells with the SAME number of chromosomes.
I. Why do cells divide?
• Fact: Living things grow, or increase in size. How does this happen?
• A living thing grows because it produces more and more cells.
• If cells simply got BIGGER, they would encounter problems!
 Materials will have trouble entering and leaving the cell
 An “information crisis” would occur! Not enough DNA to code for
all of the proteins the cell would need at a larger size.
II. What is a chromosome?
• Structures in the nucleus that contain the genetic information that is
passed on from one generation of cells to the next.
Chromosome Structure
• During the first stage of cell division, DNA replicates (copies itself)
and condenses around histone proteins to form chromosomes.
• Each chromosome is composed of 2 identical sister chromatids
attached by a centromere
Chromosome:
III. Interphase
Interphase: (“In-between” phase)
• The period between cell divisions; longest phase in the cell cycle
• Period of intense activity
• Divided into 3 phases: G1 (cell growth), S (DNA synthesis), G2
(organelles and materials required for cell division are synthesized)
IV. Mitosis
Prophase: (Piles of DNA into chromosomes)
• Chromatin condenses into distinct chromosomes, nucleolus disappears
• Nuclear envelope begins to break down
• In animals, centrioles separate and take position on opposite sides of nucleus
• Spindle begins to form
Metaphase: (Make a line)
• Chromosomes line up across the center of the cell
• Spindle fibers connect to the centromere of each chromosome
Anaphase: (Apart they go!)
• Centromeres joining the sister chromatids split
• Sister chromatids begin to separate, becoming individual chromosomes
•
Anaphase ends when the movement of chromosomes stops
Telophase: (Two cells forming)
•
Chromosomes begin to uncoil into a tangle of chromatin
•
Spindle breaks apart
•
Nuclear envelopes reform around the chromatin, forming 2 daughter nuclei
•
Mitosis is complete!
Is Cell
Division
over?
V. Cytokinesis
Cytokinesis:
•
To complete the cell cycle, the cytoplasm needs to divide!
• Cytokinesis is the division of the cytoplasm into two individual cells with
identical genetic information.
•
In plants, a cell plate gradually develops into a separating membrane.
•
The Cell Cycle is complete and will begin again!
VI. Animations
Click on the links below to view the processes of
mitosis and cytokinesis!
Mitosis Animation #1
Mitosis Animation #2
Mitosis Animation #3