Cell Division

Mitosis¹

Mitosis is the type of cell division that is used to replicate existing cells and produce exact copies.

Mitosis is used when an organism needs to heal wounds, grow, or to replace old cells.

Phases of Mitosis

Mitosis is composed of two major phases: the interphase and the mitotic phase.

Interphase²

In interphase, the cell is preparing for division. Interphase is composed of three phases.

G1 Phase³

The G1 phase is where the organelles, proteins, and centrioles⁴ replicate to accommodate the two daughter cells⁵

S Phase⁶

The S phase is where DNA replication takes place.

During the S phase, the DNA uncoiled by enzymes to allow free deoxyribonucleotides⁷ to bond and create 2 copies of the same DNA.

G2 Phase⁸

The G2 phase is when the cell doubles in size and the centriole finish replicating.

This is the step taken directly before the mitotic phase.

Mitotic Phase⁹

The mitotic phase is the final phase of cell division and consists of five major parts.

In the mitotic phase, two major events occur: mitosis— the division of the nucleus, and cytokinesis¹⁰— division of the cytoplasm

Prophase¹¹

In prophase, the chromatin¹² are condensed further into chromosomes¹³.

The centrioles begin to move to opposite poles of the cell, forming spindle fibers¹⁴.

The nuclear membrane¹⁵ also disappears; freeing the chromosomes.

Metaphase¹⁶

In metaphase, the chromosomes are attached to the spindle fibers and are aligned in the equatorial plate¹⁷.

Anaphase¹⁸

In anaphase, the chromosomes are pulled apart and separated by the spindle fibers and are pulled to opposite poles of the cell.

Telophase¹⁹

In telophase, new nuclear envelopes develop around the separated chromosomes, and the chromosomes begin to uncoil back into chromatins.

Cytokinesis

Cytokinesis is the fifth and last step of the mitotic phase and overlaps in occurrence with telophase. In this phase, the cytoplasm is separated into two, forming two new identical daughter cells.

Meiosis²⁰

Meiosis is the type of cell division that produces four partial copies of a cell.

The daughter cells produced share only a part of the mother cell’s DNA, and each only has half of the chromosomes a human cell must have.

This type of cell division is used by gametes²¹ or sex cells; and have less chromosomes and only partial traits to allow the mixing of traits from mother and father.

The produced daughter cells are called haploid cells²².

The first phases of meiosis are the same as meiosis, having an interphase and mitotic phase, but the mitotic phases are followed by a number that differentiates them (prophase I, metaphase I, etc.)

One key difference is that in prophase I, crossing over²³ occurs which is when the chromosome come into contact and exchange genetic material. This process creates genetic variation.

After mitosis I, mitosis II[^mitosisii] follows; it has the same process as mitosis, except there is no DNA replication done, and therefor it produced haploid cells.

Footnotes

1. Mitosis is the process a cell takes to produce an exact copy of itself; for healing and growing; ↩

2. Interphase is the preparatory phase of cells before division. ↩

3. G1 Phase is when the cell replicates its organelles and centrioles, and increases its protein supply. ↩

4. Centrioles are organelles that organize spindle fibers during mitosis. ↩

5. Daughter cells are the two new cells produced after cell division. ↩

6. S Phase is when DNA is replicated. ↩

7. Deoxyribonucleotides are the components that form DNA. ↩

8. G2 Phase is when the cell doubles in size and the centrioles finish replicating. ↩

9. Mitotic Phase is when the begins mitosis or the division of the nucleus. ↩

10. Cytokinesis is the division of the cytoplasm. ↩

11. Prophase is the first stage of the mitotic phase. ↩

12. Chromatin is tightly packed DNA. ↩

13. Chromosomes are tightly packed chromatins. ↩

14. Spindle fibers are microtubules that separate the chromosomes. ↩

15. The Nuclear Envelope is a membrane that surround the nucleus. ↩

16. Metaphase is the second stage of the mitotic phase. ↩

17. Equatorial plate is the center of the cell in between the centrioles. ↩

18. Anaphase is the third stage of the mitotic phase. ↩

19. Telophase is the fourth stage of the mitotic phase. ↩

20. Meiosis is the process that a sex cell takes that gives four daughter cells with only half the DNA. ↩

21. Gametes are sex cells. ↩

22. Haploid cells are cells that contain only half of the genetic materials cells have. ↩

23. Crossing over is the process where chromosomes exchange generic material; occurs during prophase I in meiosis. ↩