The Cell Cycle

Why do Cells Divide? Growth: Repair: Reproduction: To increase the number of cells in the body. Repair: To replace dead, damaged or old cells. Reproduction: Can make exact copies (clones).

Mitosis Process where cells reproduce themselves (cell division) Produces 2 identical daughter cells Is important because it ensures genetic continuity within an organism for growth, repair and development The chromosomes (in the nucleus of cell) contains the genetic information. Mitosis looks at how the chromosomes act during cell division.

The Cell Cycle: Overview There are 4 phases in the life cycle of a cell: Interphase (1st, 2nd, 3rd phases): The cell is not dividing. This is where a cell spends 90% of its life. It consists of 3 phases: G1 phase S phase G2 phase Mitosis (4th phase – M Phase): Phase where the cell divides, split into 4 stages: Prophase Metaphase Anaphase Telophase and Cytokinesis

The Chromosome A human cell has 46 chromosomes (23 pairs) Only visible when cell is dividing (mitosis) During interphase, the DNA and protein that make up the chromosomes are spread out in form of chromatin and when cell is about to divide, chromatin condenses into chromosomes. In interphase, one chromosome replicates and a sister chromatid (its identical copy) is formed. It is held together at the middle by a centromere

Interphase

Interphase: The 3 phases G1 - 1st Growth Phase Synthesis of new proteins and organelles (excluding chromosomes) S - Synthesis Phase Cell makes a whole copy of its DNA (46 chromosomes) G2 - 2nd Growth Phase Cell makes the organelles and structures needed for mitosis and checks for errors and makes repairs.

Prophase Chromatin condenses to form paired chromosomes (sister chromatids). Centrioles move towards the pole. Nucleolus disappears. Nuclear membrane breaks down.

Metaphase Spindle fibers attach to centromere. Chromosomes line up at metaphase plate (equatorial plate). Mitotic spindle complete.

Anaphase Spindle fibers shorten. Sister chromatids separate and move to opposite poles.

Telophase & Cytokinesis Mitotic spindle breaks down. Chromosomes loses its distinct shape and nucleus reforms. Cell membrane pinches inwards forming a cleavage furrow in animal cells. In plant cells, cell plate forms the cell wall/cell membrane. Cytoplasm splits in half (cytokinesis). One cell becomes two new daughter cells Cells return to interphase at G1.

Animal vs. Plant Cell

Identify the Stages of Mitosis Cytokinesis Interphase Anaphase! Telophase Prophase Metaphase