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Cell Cycle
Cell DivisionCell division is the process where a parent cell divides into two daughter cells.There are two types of cell division:
Mitosis occurs in somatic cells.Meiosis occurs in the sex organs and produces sex cells (gametes).
Sperm
Ovum (egg)
Introduction to MitosisDuring mitosis, an existing parent cell divides into two new daughter cells (right).
The cells are genetically identical.
There is no change in chromosomal number.
Cells are diploid, containing two setsof chromosomes.
In humans the diploid number is 46
Mitosis is associated with the growth and repair of somatic cells in the body.
The cell cycle
Mitosis is just one phase of the cell cycle. There are three main phases in the cell cycle:
Interphase (three stages)Mitosis (nuclear division)Cytokinesis (division of the cytoplasm)
Mitosis and the Cell Cycle
Interphase
Mitosis
C
Cytokinesis
InterphaseInterphase accounts for 90% of the cell cycle.
It is the longest phase of the cell cycle.
Interphase consists of three stages:
Growth 1: G1
The cell grows and develops
Synthesis (S)The cell duplicates its geneticmaterial (chromosomes).
Growth 2: G2
Further growthG0
Nondividing state
M
G1
G2
S
C
The cell cycle
Nuclear membrane
Centrosome is replicated
Chromosome
Nucleolus
MitosisThe mitotic cycle is broken down into six phases.
AnaphaseLate AnaphaseTelophase
Early Prophase Late Prophase Metaphase
Mitosis: Early ProphaseProphase is the first stage of mitosis. In early prophase:
the nuclear membrane disintegrates
the nucleolus disappears
the chromatin condenses into visible chromosomes.
Replicated centrosomes
Nucleolus disappears
Nuclear membrane disintegrates
Mitosis: ProphaseIn late prophase:
the chromosomes continue to coiland appear as double chromatids.the chromatids are each joined by a centromere.the centrosomes (including centrioles in animal cells) move to opposite ends of the cell. As they do so, they form the mitotic spindle between the poles.
Centromere
Centrosome
Chromatids
Mitosis: MetaphaseDuring metaphase the chromosomes become aligned at the equator of the cell.
Mitotic spindle
Chromosomes
Mitosis: Early AnaphaseIn anaphase, the sister chromatids split and the chromosomes are pulled to opposite poles of the cell.
Chromosomes Spindle
Anaphase is the shortest mitotic phase
Mitosis: Late Anaphase
By late anaphase, the chromosomes have moved to opposite poles.By the end of anaphase, the two poles of the cell have equivalent, and complete, collections of chromosomes.
Mitotic spindle
Chromosomes
Centrosome
Mitosis: Telophase
Telophase is characterized by the formation of two new nuclei.
The nucleoli reappear and the chromatin becomes less tightly coiled (less condensed). In plant cells, the cell plate forms
where the new cell wall will form.
Cytokinesis
The division of the cytoplasm is termed cytokinesis.Cytokinesis begins towards the end of telophase.
In plant cells, the cell plate forms where the new cell wall will form.In animal cells, a cleavage furrow pinches the cell in two.
Nucleus
Cell wall
Two cells are formed
Mitosis: ReviewInterphase
Cytokinesis
Early Prophase Late Prophase
Metaphase
Chromosomes line up on the metaphase plate.
Chromosomes separate to opposite poles.
Cell elongates
Chromosomes appear as chromatids.Mitotic spindle forms.Centrosomes move to opposite poles.
Two independent cells.
Nuclei reform.Cell plate forms (plants)
Telophase Late Anaphase
Cell enters mitosis
Anaphase
DNA continues condensing.Nuclear membrane disintegrates.Nucleolus disintegrates.
DNA replicated.Centrosome replicated.Nucleus still well defined.
Mitosis in the Root Tip
Mitosis in plant cells occurs only in regions of meristematic tissue.
The meristematic tissue is located at the tip of every stem and every root.
In contrast, mitosis can occur throughout the body of a growing animal.
Zone of specialization
Zone of elongation
Zone of cell division
Meristematic tissue (area of cell division)
Root cap
Root tip growing in this direction
