Chapter 10-2Chapter 10-2

• Chromosomes are not visible in cells Chromosomes are not visible in cells until cells begin the process of cell until cells begin the process of cell division.division.

• Chromosomes consist of two Chromosomes consist of two identical sister chromatids.identical sister chromatids.

• A centromere holds the two sister A centromere holds the two sister chromatids together at their centers.chromatids together at their centers.

• Cell CycleCell Cycle

• The cell goes through a stage called The cell goes through a stage called interphase between cell divisions.interphase between cell divisions.

• Cells grow and then divide in a Cells grow and then divide in a series of events called the cell series of events called the cell cycle.cycle.

•MM phase is the when the nucleus phase is the when the nucleus divides.divides.

• Interphase consists of:Interphase consists of:

• GG11 phase phase

• S phaseS phase

• GG22 phase phase

• GG11 phase - cells do most of their phase - cells do most of their growing.growing.

• S phaseS phase

• GG22 phase phase

MitosisMitosis

•Four phases: Four phases: –ProphaseProphase–MetaphaseMetaphase–AnaphaseAnaphase–TelophaseTelophase

MitosisMitosis

• Centrioles Centrioles are the tiny structures are the tiny structures located in the cytoplasm near the located in the cytoplasm near the nuclear envelope at the beginning of nuclear envelope at the beginning of prophase.prophase.

MitosisMitosis

• Spindle Spindle – is the fanlike microtuble – is the fanlike microtuble structure that helps separate the structure that helps separate the chromosomes.chromosomes.

MitosisMitosis

• During Prophase:During Prophase:

•

• the chromosomes become visible in the chromosomes become visible in the nucleus; the nucleus;

• the centrioles take up positions on the centrioles take up positions on opposite sides of the nucleus.opposite sides of the nucleus.

MitosisMitosis

• During Metaphase:During Metaphase:

• The chromosomes line up in the The chromosomes line up in the center of the cell.center of the cell.

MitosisMitosis

• During Anaphase :During Anaphase :

• The chromosomes move until they The chromosomes move until they form two separate form two separate

• Forming groups at opposite poles of Forming groups at opposite poles of the spindle.the spindle.

MitosisMitosis

• During Telophase:During Telophase:

• the nuclear envelope re-forms around the nuclear envelope re-forms around each cluster of chromosomes; each cluster of chromosomes;

• the nucleolus becomes visible in each the nucleolus becomes visible in each daughter nucleus.daughter nucleus.

CytokinesisCytokinesis

• CytokinesisCytokinesis is the division of the is the division of the cytoplasm.cytoplasm.

CytokinesisCytokinesis

• How does it happen in animals?How does it happen in animals?

• The membrane is drawn downward The membrane is drawn downward until it is pinched into nearly two until it is pinched into nearly two equal parts.equal parts.

CytokinesisCytokinesis

• A A cell platecell plate is formed midway is formed midway between the divided nucleus during between the divided nucleus during cytokinesis in plant cells.cytokinesis in plant cells.