The Cell Cycle

1
The Cell Cycle

• Biology B/DNA and the Cell Cycle

2
Limits to Cell Growth

• As living organisms grow, so do their cells.
• As cells get larger, eventually they must divide
  for two reasons
• DNA overload As a cell gets large, its DNA
  cannot hold all the information necessary for the
  cell to run properly.
• Movement of materials Materials have to travel
  too far to get from the cell membrane to the
  nucleus. The cell becomes inefficient.

3
Preparing for Cell Division

• As cells prepare for division the DNA that was
  loose in the nucleus folds into chromosomes.

4
The Cell Cycle

• At any given time in a cells life it is either
  dividing or not dividing.
• The periods of time when cells are not dividing
  are called Interphase.
• The periods of time when cells are dividing is
  referred to as the M phase.

5
Interphase

• There are three important things that happen
  during Interphase
• Cell Growth
• DNA Replication (in preparation for cell
  division)
• Preparation for the M phase
• Interphase usually lasts longer than the M phase

6
Interphase
7
M Phase

• The M in M phase stands for Mitosis, which is
  the process of cell division.
• Mitosis is divided into four phases that happen
  one after the other
• Prophase
• Metaphase
• Anaphase
• Telophase

8
Prophase

• Prophase is the longest of the phases of mitosis.
• Chromosomes appear during prophase.
• Centrioles (two tiny organelles in animal cells)
  move away from the nuclear envelope and towards
  opposite ends of the cell and a spindle (fiber)
  forms between them
• The nuclear envelope breaks down.

9
Prophase
10
Metaphase

• Metaphase lasts only a few minutes.
• The centromeres of the chromosomes attach to the
  spindles in the center of the cell.

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Metaphase
12
Anaphase

• Sister chromatids (that make up the chromosomes)
  separate and move along the spindles to opposite
  sides of the cell.
• The chromatids now become individual chromosomes
• Anaphase ends when the chromosomes stop moving.

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Anaphase
14
Telophase

• Telophase is the final phase of mitosis
• The chromosomes unfold into loose groupings of
  DNA.
• Nuclear envelopes re-form around the DNA at each
  end of the cell.
• The spindle breaks down.

15
Telophase
16
Cytokinesis

• There is one last part to the M phase and the
  completion of cell division.
• During cytokinesis the cytoplasm splits to form
  two separate cells.
• In animal cells, the cytoplasm actually splits
  off.
• In plant cells a cell plate forms in the middle
  of the dividing cell.

17
Cytokinesis