The Cell Cycle

For life to go on, cells need to make copies of themselves. Whether they are unicellular or multicellular, prokaryotic or eukaryotic, cells must have time to carry out their functions, copy their parts, then divide into two relatively equal cells. Those two cells must then function, grow, and divide, thus every cell has a cycle of events that it repeats in living things.

Cells need to divide so that multicellular organisms can Grow, and Repair damaged tissue, and that unicellular organisms can Reproduce.
Interphase is the longest part of the cell cycle in which the cell performs its normal tasks
Mitosis is the process of copying the nucleus
Cytokinesis is the process of actually dividing one cell to make two cells
Cells must have a way of controlling the cell cycle

Making More of Themcellves

The cell cycle is the pattern of stages that cells go through during their lives. Some can repeat the entire cycle in 20 minutes, others never get out of the very first stage.

Interphase - normal cell time has 3 sub-stages
- G1 - during this time, cells grow in size and carry out all of their normal functions like respiration and protein synthesis. (G = growth)
- S - Sometime in G1, a cell will get a signal that it is time to divide. The first step in making a new cell is to copy the DNA of the original cell (replication). (S = Synthesis/ making DNA)
- G2 - Now that the cell has extra DNA, it needs to grow in size and copy organelles for the new cell.
M-Phase - Actions necessary for dividing the cell
- Mitosis - Dividing the nucleus
  - Prophase
  - Metaphase
  - Anaphase
  - Telophase
- Cytokinesis - Dividing the cell

The cell cycle is controlled by a series of checkpoints. Each "checkpoint" is caused by a buildup of chemicals that stimulate enzymes and allow the cell to move on. For example, growth factors are chemicals that signal a cell to divide; often originate outside the cell. Each checkpoint is like a series of questions that, if correct, allow the cell to move on in the cycle.

G1 Checkpoint - Does the cell need to divide? is the DNA damaged?
G2 Checkpoint - Did the DNA copy correctly? Is the cell big enough to divide?
Metaphase Checkpoint - Did the copies of DNA line up correctly?