Why Do Cells Need To Divide?  It depends on the organism  Unicellular organisms like bacteria (prokaryotes) divide to reproduce  Multicellular organisms (most eukaryotes) use it to grow larger and repair damaged cells.

Differentiation  All the cells in your body have the same DNA  The fertilized egg (zygote) that made you divided many times.  The resulting cells differentiated into all the different cell types you have by turning on certain genes in your DNA.

3 Types of Cell Division 1. Binary fission-cell division in prokaryotes 1. Binary fission-cell division in prokaryotes 2. Cell Cycle (with Mitosis)-cell division in eukaryotes 2. Cell Cycle (with Mitosis)-cell division in eukaryotes 3. Meiosis—cell division to form sex cells (egg and sperm) 3. Meiosis—cell division to form sex cells (egg and sperm)

Prokaryotes  Divide by binary fission  Circular DNA  Results in two cells genetically the same  What has to take place before any cells divide?

3 Types of Cell Division 1. Binary fission-cell division in prokaryotes 1. Binary fission-cell division in prokaryotes 2. Cell Cycle (with Mitosis)-cell division in eukaryotes 2. Cell Cycle (with Mitosis)-cell division in eukaryotes 3. Meiosis—cell division to form sex cells (egg and sperm) 3. Meiosis—cell division to form sex cells (egg and sperm)

Eukaryotes The Cell Cycle The Cell Cycle –Growth –Repair or replacement of cells. –Control size so nutrients can get in and waste can get out in a timely fashion Some cells die quickly and need to be replaced a lot (skin cells). Some cells die quickly and need to be replaced a lot (skin cells). Some cells never get replaced (nerve cells). Some cells never get replaced (nerve cells). Some organisms can regenerate whole body parts. Some organisms can regenerate whole body parts.

Each cell goes through a series of phases throughout its life. Each cell goes through a series of phases throughout its life. The cell cycle-all events between one cell division and the next The cell cycle-all events between one cell division and the next –**ONE REPLICATION & ONE DIVISION –Result? 2 daughter cells genetically exact to the parent cell they came from.

2 basic steps: Interphase (G1, S, G2) and Mitosis (M) 2 basic steps: Interphase (G1, S, G2) and Mitosis (M) –Interphase: the longest part of cell cycle composed of G1, S, G2 stages –M=Mitosis = Nuclear division

First step of Interphase First step of Interphase G1 (G=gap) G1 (G=gap) Cell going through intense growth using lots of food and energy. Cell going through intense growth using lots of food and energy. DNA at this point is unwound and called chromatin DNA at this point is unwound and called chromatin

Second step in Interphase Second step in Interphase S=Synthesis phase. S=Synthesis phase. All DNA replicated during this phase  cell has double the genetic material All DNA replicated during this phase  cell has double the genetic material Sister chromatid- one of two identical parts of a replicated chromosome Sister chromatid- one of two identical parts of a replicated chromosome

Third step in Interphase Third step in Interphase G=gap G=gap Cell grows some more. Cell grows some more. Extra organelles are being made. Extra organelles are being made.

After Interphase (G1, S, and G2) After Interphase (G1, S, and G2) M=Mitosis M=Mitosis Mitosis = Nuclear division. Mitosis = Nuclear division. MITOSIS IS ONLY THE DIVISION OF THE NUCLEUS DURING THE CELL CYCLE!!! MITOSIS IS ONLY THE DIVISION OF THE NUCLEUS DURING THE CELL CYCLE!!! There are four mitotic steps: There are four mitotic steps: –Prophase –Metaphase –Anaphase –Telophase.

Prophase DNA coils up into visible chromosomes DNA coils up into visible chromosomes Nuclear envelope disappears. Nuclear envelope disappears. Spindle fiber forms from the centrioles. Spindle fiber forms from the centrioles.

Metaphase Chromosomes begin to line up at the equator of the cell. Chromosomes begin to line up at the equator of the cell. Spindle fibers attach to the centromere of each sister chromatid of the chromosome. Spindle fibers attach to the centromere of each sister chromatid of the chromosome.

Anaphase Spindle fibers begin to pull apart sister chromatids. Each is now a chromosome Spindle fibers begin to pull apart sister chromatids. Each is now a chromosome Spindle breaks down after this. Spindle breaks down after this.

Telophase Each side now has a full set of chromosomes. Each side now has a full set of chromosomes. Nuclear envelope will reform. Nuclear envelope will reform.

Cytokinesis “Cytokinesis”—division of cytoplasm at the end of the cell cycle which cleaves the cell in half. “Cytokinesis”—division of cytoplasm at the end of the cell cycle which cleaves the cell in half. Animal cells form a “furrow.” Animal cells form a “furrow.” Plant cells form a new cell wall. Plant cells form a new cell wall. Formation of two, identical daughter cells with 46 chromosomes Formation of two, identical daughter cells with 46 chromosomes

Overall Cell Cycle Process Interphase (G1, S, G2) and Mitosis (Prophase, Metaphase, Anaphase, Telophase)  IPMAT Interphase (G1, S, G2) and Mitosis (Prophase, Metaphase, Anaphase, Telophase)  IPMAT Cell Cycle Animation Cell Cycle Animation Cell Cycle Animation Cell Cycle Animation

REGULATION OF CELL CYCLE  Cell division controlled by certain proteins called cyclins  Cancer cells don’t respond to the cyclin signals--- uncontrolled growth (tumors)  Benign tumors stay intact  Malignant tumors spread throughout body (metastasize)