Cell ReproductionCell Reproduction

MitosisMitosis

Why is Cell Division Why is Cell Division Important?Important?

In humans cell division is needed for:In humans cell division is needed for:

1.1. RepairRepair

2.2. Growth Growth

3.3. Replacement like skin and bone Replacement like skin and bone cells.cells.

4.4. Cell division is important to one-Cell division is important to one-celled organisms, too—it’s how celled organisms, too—it’s how they reproduce themselves.they reproduce themselves.

The Cell CycleThe Cell Cycle

A life cycle begins with the A life cycle begins with the organism’s formation, is followed organism’s formation, is followed by growth and development, and by growth and development, and finally ends in death.finally ends in death.

The cell cycleThe cell cycle is a series of events is a series of events that takes place from one cell that takes place from one cell division to the next.division to the next.

InterphaseInterphase

Most of the life of Most of the life of any eukaryotic cellany eukaryotic cell—is spent in a —is spent in a period of growth period of growth and development and development called interphase.called interphase.

Cells in your body Cells in your body that no longer that no longer divide, such as divide, such as nerve and muscle nerve and muscle cells, are always in cells, are always in interphase.interphase.

InterphaseInterphase

The cell grows- doubles in sizeThe cell grows- doubles in size DNA is replicatedDNA is replicated Chromatin-threadlike coils of DNA Chromatin-threadlike coils of DNA

strung out within the nucleus strung out within the nucleus condensecondense into compacted bodies into compacted bodies of chromosomes.of chromosomes.

Centrioles replicate- most plants Centrioles replicate- most plants do not have centrioles.do not have centrioles.

InterphaseInterphase

Before a cell divides, Before a cell divides, a copy of the a copy of the hereditary material hereditary material must be made so that must be made so that each of the two new each of the two new cells will get a cells will get a complete copy.complete copy.

Each cell needs a Each cell needs a complete set of complete set of hereditary material to hereditary material to carry out life carry out life functions.functions.

InterphaseInterphase

• A chromosome (KROH muh sohm) is a structure in the nucleus that contains hereditary material.

• During interphase, each chromosome duplicates.

InterphaseInterphase

When the nucleus When the nucleus is ready to divide, is ready to divide, each duplicated each duplicated chromosome coils chromosome coils tightly into two tightly into two thickened, thickened, identical strands identical strands called chromatids.called chromatids.

MitosisMitosis

Mitosis process in which the nucleus Mitosis process in which the nucleus divides to form two identical nuclei. divides to form two identical nuclei. Each new nucleus also is identical to Each new nucleus also is identical to the original nucleus.the original nucleus.

The steps of mitosis in order are The steps of mitosis in order are named:named:

1.1. prophase prophase 2.2. metaphasemetaphase3.3. anaphaseanaphase4.4. telophasetelophase

1. Prophase-mitosis 1. Prophase-mitosis beginsbegins• Chromatids are fully

visible when viewed under a microscope.

• Nucleolus and the nuclear membrane disintegrate.

• Centrioles move to Centrioles move to opposite ends of the cellopposite ends of the cell

• Threadlike spindle fibers begin to stretch across the cell.

• Plant cells do not have centrioles.

2. Metaphase- 2. Metaphase- chromosome attach to chromosome attach to the spindle.the spindle.• The pairs of

chromatids line up across the center of the cell

• The centromere of The centromere of each pair becomes each pair becomes attached to two attached to two spindle fibers—one spindle fibers—one from each side of from each side of the cell.the cell.

3. Anaphase- 3. Anaphase- chromosomes begin to chromosomes begin to separate.separate.• Each centromere

divides and the spindle fibers shorten.

• Each pair of Each pair of chromatids separates, chromatids separates, and chromatids begin and chromatids begin to move to opposite to move to opposite ends of the cell.ends of the cell.

• The separated The separated chromatids are now chromatids are now called chromosomes.called chromosomes.

4. Telophase- two new 4. Telophase- two new nuclei form.nuclei form.In the final step,

telophase:• Spindle fibers start

to disappear.• The chromosomes

start to uncoil.• A new nucleus

forms.

Cytokenis- Two new Cytokenis- Two new daughter cells form.daughter cells form.• After the nucleus

has divided, the cytoplasm separates and two new cells are formed.

• The cell membrane pinches in the middle, like a balloon with a string tightened around it, and the cytoplasm divides.

CytokinesisCytokinesis

• In plant cells, the appearance of a cell plate tells you that the cytoplasm is being divided.

• New cell walls form along the cell plate, and new cell membranes develop inside the cell walls.

• Following division of the cytoplasm, most new cells begin the period of growth, or interphase, again.

Results of MitosisResults of Mitosis

• Mitosis is the division of the nucleus, and it produces two new nuclei that are identical to each other and the original nucleus.

Results of MitosisResults of Mitosis

• Each new nucleus has the same number and type of chromosomes.

• Every cell in your body, except sex cells, has a nucleus with 46 chromosomes—23 pairs.

Results of MitosisResults of Mitosis

• Each of the trillions of cells in your body, except sex cells, has a copy of the same hereditary material.

• All of your cells use different parts of the same hereditary material to become different types of cells.

Results of MitosisResults of Mitosis

• Cell division allows growth and replaces worn out or damaged cells.

• If you cut yourself, the wound heals because cell division replaces damaged cells.

• Another way some organisms use cell division is to produce new organisms.