1. Cell Biology Lec.6 Date: 25-12-2012 Dr:Buthaina Al-Sabawi
Cell division
Mitosis is the division of a somatic cell into two daughter cells.

2. There are two types of cell division
Mitosis: Occurs in somatic cells
Meiosis: Occurs in germ cells
Mitosis:
Mitosis produces two daughter cells that are identical to the parent cell.  If the parent cell is haploid (N), then the daughter cells will be haploid.   If the parent cell is diploid, the daughter cells will also be diploid.
N N
2N N

3. This type of cell division allows multicellular organisms to grow and repair damaged tissue
Mitotic is nuclear division plus cytokinesis.
The parent cell divides, and each of the daughter cells receives a chromosomal karyotype identical to that of the parent cell.
Karyotype show all the chromosomes lined up in pairs.XY, the sex chromosomes of a male. Female have two identical X (XX) chromosomes.

4. Mitosis taking about (45 - 90 minutes)
The other non-sex chromosomes are called autosomes and in the man there are 22 pairs.
Mitosis taking about ( minutes)
N. appears as its normally observed in microscope preparation.
Chromosomes are decondensed (chromatids)
Nucleus appears morphologically uniform. Although a dark spot called the nucleolus may be visible.
In molecular level (cell growth, DNA replication, centrosomes duplication)
Mitosis is dynamic & continuous

5. Prophase
In this stage, the chromatin begins to shorten and condense due to coiling, to form chromosome Each chromosomes (duplicated during interphase). Centrioles start moving to the opposite ends of the cell and the spindle fibers extend from the centromeres (condensed region of each chromosome). The nuclear membrane and nucleolus can no longer be seen now.

6. Metaphase
Prometaphase begins with the breakdown of the nuclear envelope.
During prometaphase, three different types of microtuble fibers together form mitotic spindle, all of these microtubles originate from the centrosomes, which function as the two poles of the spindle apparatus.
1-Microtubles that extend between a centrosome and the the kinetochore of a chromatid are called kinetochore microtubles, or centromeric fibers.

8. 2-Microtubles from each centromsome that are directed toward the middle of the cell are polar microtubles, polar microtubules originating on opposite centrosomes interdigitate near middle of the cell.
3- Astral microtubles that extend out from the centrosome toward the cell periphery

9. Each kinetochore contains proteins (nuclear motors), enabling the chromosome to slide along the microtubules.
Nucleolus disappear. The chromosomes migrate to the equatorial plane of the cell. Where each divides longitudinally to form chromatids.
The chromatids attach to the microtubules of the mitotic spindle.

10. Anaphase
In this phase, as the spindle fiber shorten and the centromere splits, the paired chromosomes will separate and start moving to the opposite sides of the cell, giving rise to two daughter chromosomes, daughter chromosomes, each with a centromere and single chromatid, being to move toward opposite poles.
What accounts for the movement of the daughter chromosomes ?
First: the polar spindle fibers lengthen as they past one another.

12. Second: the kinetochore spindle fibers disassemble at the region of the kinetochores, and this pulls the daughter chromosomes to the pole.
Telophase
During telophase, the spindle disappears .
New nuclear envelopes form around the daughter chromosomes. The daughter nucleus contains the same number and kinds of chromosomes as the original parent cell. Polar spindle fibers are still visible
chromosomes become diffuse, nucleolus appears in each nucleus s.

14. While these alteration are taking place a constriction develops at the equatorial plane of the parent cell and progress until the cytoplasm and its organelles are divided in two.
Microfilaments containing actin add myosin accumulates in a belt-like (contractile ring).
Contraction pulls the plasma membrane progressively in ward, and pinching the cell in two equal halves.
Contractile ring disappears completely.
Parental cell generates two daughter cells that have the same number and kind of chromosomes as each and as the original parental cell.