CELL DIVISION &

MITOSIS

MITOSIS Process in which a cell’s nucleus replicates and divides in preparation for division of the cell

Results in two cells that are genetically identical (daughter cells)

MITOSIS IS VITAL FOR: Growth Repair & replacement of damaged or worn out cells

Asexual reproduction Reproduction without eggs & sperm

Mitosis continues in full grown organisms as a means of maintaining the organism

Ex: replacing dying skin cells or repairing damaged muscle cells

In the cells of the adult human body, mitosis occurs about 25 million times per second.

Mitosis is the sole mode of reproduction for many single-celled organisms.

The life cycle of eukaryotic cells is a continuous process typically divided into three phases:

1. interphase2. mitosis3.cytokinesis.

INTERPHASE Occurs before mitosis Includes three stages : G1, S, and G2 stages of the cell

cycle

Chromosomes are not clearly visible here

INTERPHASEAnimal Cell Plant Cell

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

IMPORTANT CELL STRUCTURES INVOLVED IN MITOSIS

Chromatid – each strand of a duplicated chromosome

Centromere – the area where each pair of chromatids is joined

Centrioles – tiny structures located in the cytoplasm of animal cells that help organize the spindle

Spindle – a fanlike microtubule structure that helps separate the chromatids

Animated Mitosis Cyclehttp://www.cellsalive.com/mitosis.htm

• Interphase• Prophase• Metaphase• Anaphase• Telophase & Cytokinesis

MITOSIS OCCURS IN 4 STEPS

1.Prophase2.Metaphase3.Anaphase4.Telophase

PROPHASE Replicated DNA strands slowly wrap around proteins that coil & condense into two short, thick, rodlike structures called chromatids,

Chromatids are attached by a centromere.

Chromosomes 1st appear here

Centrioles (one located on each side of the nucleus) separate & move toward opposite poles of the cell, radiating thin, hallow, proteins microtubules

Microtubules arrange themselves in a spindle that spans the cell with the widest part at the center and narrower ends at the opposite poles

The nuclear membrane breaks down into tiny sacs that are dispersed in the cytoplasm.

Final digestion of the membrane marks the beginning of metaphase.

PROPHASEAnimal Cell Plant Cell

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Spindle fibers

Centrioles

METAPHASE Spindle fibers attach to chromatids near the centromeres so they line up at the equatorial plane of the cell halfway between the poles.

One chromatid faces one pole of the cell while its partner faces the opposite pole.

METAPHASEAnimal Cell Plant Cell

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

ANAPHASE Begins when the centromeres split & move along the spindle fibers to opposite poles of the cell.

Cytokinesis is said to start here. It begins to split the two new cells as the cells are still dividing.

ANAPHASEAnimal Cell Plant Cell

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

TELOPHASE Begins as the two identical groups of single chromosomes gather at opposite poles of the cell

Spindle fibers break down and newly formed chromosomes begin to unwind and spread out into a tangle of chromatin.

Shortest phase of Mitosis

A new nuclear membrane forms around each new group of chromosomes. A nucleolus becomes visible in each daughter nucleus.

TELOPHASEAnimal Cell Plant Cell

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Mitosis accomplishes replication and division of the nucleus, but the cell has yet to divide

Animal Mitosis -- Review

Interphase

                                              

              

Prophase

                                             

               

Metaphase

                                              

              

Anaphase

                                             

               

Telophase

                                              

              

Interphase

                                             

               

Plant Mitosis -- Review

Interphase

                                                        

    

Prophase

                                                       

     

Metaphase

                                                        

    

Anaphase

                                                       

     

Telophase

                                                        

    

Interphase

                                                       

     

CYTOKINESIS Final stage of the cell cycle

Timing of this stage varies depending on cell type

It can begin during anaphase and finish in telophase, or it can follow telophase

The cell’s cytoplasm separates in half with each half containing one nucleus

CYTOKINESIS IN ANIMAL CELLS

The cell membrane pinches in, creating a cleavage furrow, until the mother cell is pinches in half.

CYTOKINESIS IN PLANTS In plants, the cell membrane is not

flexible enough to draw inward because of the rigid cell wall.

Cellulose & other materials that make up the cell wall are transported to the midline of the cell and a new cell wall is constructed.

END RESULTS! The process of DNA replication, precise alignment of the chromosomes in mitosis, and the successful separation of identical chromatids in anaphase results in two new cells that are genetically identical.

The new cells enter interphase, and the cell cycle begins again.

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CELL CYCLE

MITOSIS ANIMATION

http://www.cellsalive.com/mitosis.htm

http://www.youtube.com/watch?v=nPG6480RQo0&feature=related