5 Mitosis

Mitosis Duplication and Division

Importance of Mitosis 

Individual cells may be functionally short-lived  Ex.



Skin cells - - Liver cells

Constantly duplicating while maintaining the chromosomal set  Alike

in composition – DNA  Equal in number to the parent cell. 

Cannot lose genetic instructions  “Memory"

of which genes were active prior to entry into mitosis are transmitted to the daughter cells.

Cell cycle 

Two main periods  Mitotic

phase is a relatively short actionpacked period.  Interphase Much longer period, where the cell prepares itself for division.  The cell grows by producing proteins and cytoplasmic organelles 

Chromosome Replication 

When a chromosome divides into identical chromosomes, the chromatids remain attached at their centromere.



DNA unzips and is duplicated Sister Chromatids

Homologous Chromosomes

Interphase Stage between cell divisions  Divided into three phases 

 G1

(first gap) - a cell grows  S (synthesis) - continues to grow as some DNA is replicated 

The chromosomes begin to replicate

 G2

(second gap) - grows more and prepares for mitosis

Mitotic Phase 

Mitosis  Process

by which a cell separates its duplicated genome into two identical halves.



Cytokinesis  Divides

the cytoplasm and cell membrane  Results in two identical daughter cells with a roughly equal distribution of organelles and other cellular components.

Mitosis - 5 subphases     



Prophase Prometaphase Metaphase Anaphase Telophase Impossible to discern an exact "start" and "stop" of the phases.

Prophase 

Chromatin  Small

granular particles in the nucleus begins to condense  Become visible in the light microscope as chromosomes. 

The nucleolus disappears.

Prophase 

Centriole  Cytoplasmic

organelle – divides into two  Begin moving to opposite ends of the cell  Fibers extend from the centromeres. 

Spindle fibers  Long

protein molecules  Form a three dimensional arch across the cell between the two bodies

Prometaphase The nuclear membrane dissolves  Proteins attach to the centromeres creating the kinetochores. 

 links

the chromatids to microtubule polymers from the mitotic spindle

Prometaphase 

Chromosome number is temporarily double – tetraploid  Chromatids

become thicker  Can identify lengths and location of centromeres 

Kinetochores of each chromatid move to the spindles equator

Prometaphase

Metaphase

Metaphase Spindle fibers align the chromosomes along the middle of the cell – metaphase plate.  Necessary to ensure when the chromatids are separated, each new nucleus will receive one copy of each chromosome 

Anaphase 

The paired chromatids separate at the kinetochores and move to opposite sides of the cell.

Anaphase 

Even alignment is due to the counterbalance of the pulling powers generated by the opposing kinetochores, analogous to a tug-of-war between equally strong people

Telophase Chromatids arrive at opposite poles of cell – now sister chromosomes  A cleavage furrow (pinch) containing a contractile ring develops where the metaphase plate used to be  New membranes form around the daughter nuclei. 

Telophase The chromosomes disperse and are no longer visible under the light microscope.  The spindle fibers disperse. 

Cytokinesis A fiber ring composed of actin (protein) is formed around the center of the cell  Contracts pinching the cell into two daughter cells, each with one nucleus. 

Review 

Each daughter cell has a complete copy of the genome of its parent cell.

Review Interphase