The Cell Cycle Ch. 10

CELL CYCLE Life cycle of cells 2 Stages Interphase Cell Division

Importance of Cell Division According to the cell theory, new cells can only arise from existing cells. There are several cases when new cells are needed, such as:

1) Reproduction For single celled organisms, like prokaryotes (bacteria), cell division is used for reproduction. Asexual

2) Growth For multicellular organisms, cell division allows growth. We all started as one cell, but we needed many new cells.

3) Cell Replacement As cells age, they wear out and die. New cells are needed to replace them.

4) Repairing Wounds If a multicellular organism is injured, the damaged cells need to be replaced.

Stage 1 & 2 of the Cell Cycle

Interphase – 1st stage

After new cells are formed, they need time to grow and prepare for another round of cell division – this is Interphase.

Stages of Interphase G1 S G2

G1 phase Gap 1 Cell growth Increases in size and makes new proteins and organelles.

S phase Synthesis DNA replication

G2 phase Gap 2 Prepare to divide make more organelles

Cell Division – 2nd Stage

Period during which cells replicate and divide. Consists of Mitosis and Cytokinesis Called the M phase.

Mitosis

Mitosis The process that copies the nucleus Results in one cell with two identical nuclei

4 Stages of Mitosis Prophase Metaphase Anaphase Telophase

P M A T Matt Mitosis

PROPHASE Chromatin condenses to chromosomes. Nucleolus disappears. Nuclear membrane breaks down.

METAPHASE Chromosomes line up in the middle of the cell

ANAPHASE Sister chromatids are pulled apart.

TELOPHASE Chromosomes return to chromatin. Two identical nuclei form. Nucleolus reappears. Nuclear membrane reforms.

Cytokinesis

Cytokinesis Process that divides the cytoplasm and the organelles Results in two genetically identical daughter cells (each with one nucleus)

In cells without cell walls The cell membrane pinches in half forming two separate cells.

In cells with cell walls A new piece of cell wall must be formed to separate the two new cells.

Controlling the cell cycle Cell division is carefully controlled by: The P53 gene Cyclins (special proteins) Cell-to-cell contact

When cells go wild!!! If cells do not stop dividing when they get the signal to, they become cancerous Often caused by a defect in the P53 gene

Cancer Cells Divide uncontrollably Live much longer than normal cells Crowd out healthy cells, allowing the cancer to spread Are difficult to treat because they are YOUR cells – they just don’t listen to your body anymore