MCAT Biology > Mitosis

Background

Mitosis - Cell Cycle Diagram

Diploid cells (2n) are autosomal cells, with ½ the genetic material coming from the father and ½ coming from the mother

Haploid cells (n) are sex cells and only have ½ of the normal amount of genetic material

Feature Diploid Haploid
Genetic Material 2n (Two Complete Chromosome Sets) n (One Complete Chromosome Sets)
Reproduction Methods Mitosis (Direct Replication) Meiosis (Sexual Reproduction)
Cell Types Skin, Blood, Muscle Cells (Somatic Cells) Sperm, Ovum (Gamete Cells)
Mitosis - Mitosis

Interphase

G1 Phase

Mitosis - Interphase G1

G1 (growth) begins when cells created organelles for energy (mitochondria) and protein production (ribosomes, endoplasmic reticulum). The cell also increases in general size during this period.

S Phase

Mitosis - Interphase S

S (synthesis) begins when the cell passes the G1 restriction point and replicates its genetic material so the daughter cells with have identical copies. Each chromosome is 2 sister chromatids bound at a centromere. On the centromere there is a protein unit called the kinetochore where the spindle fibers attach in order to pull the two sister chromatids apart.

The main structures that are responsible for pulling the sister chromatids apart are the centrioles, asters and spindle fibers.

There is twice as much DNA as the cell has in G1. This means that the sex cell has 46 pairs of chromosomes and 96 sister chromatids. The centrioles are also synthesized and created during this period.

G2 Phase

Mitosis - Interphase G2

G2 is the phase of quality control and organelles and cytoplasm levels increase in anticipation of division. Some cells such as nerve and muscle cells do not divide and instead enter the G0 phase. Unregulated division after this point causes cancer. Examples of cells that are in G0 phase are nerve and muscles.

Mitosis

Prophase

Mitosis - Prophase

First, the chromosomes condense and the centriole pairs separate and move towards the opposite ends of the cel to form the spindle apparatus. Next, the nuclear membrane disappears and the kinetochores with the fibers appear at the centromere. There are the same amount of chromosomes (46) and sister chromatids (96) as in the S phase.

Pro-Metaphase

Mitosis - Pro-Metaphase

Metaphase

Mitosis - Metaphase

First the centriole pairs move to the opposite poles of the cells. Next the kinetochores interact with the spindle apparatus to align the chromosomes at the metaphase plate, which is equidistant from the poles. There is still the same number of chromosomes as originally present in the S phase.

Anaphase

Mitosis - Anaphase

First the centromeres split and the sister chromatids separate. The telomeres are the last to split. The chromatids are pulled apart by the shortening of the kinetochores and now there are still 2 chromosomes but 4 sister chromatids per cell that is about to be formed.

Telophase

Mitosis - Telophase

First the spindle apparatus disappears and the nuclear membrane reforms. Next the chromosomes uncoil and cytokinesis occurs and separates the cytoplasm.

Cytokinesis

Mitosis - Mitosis Cytokinesis

Cytokinesis occurs when the cell pinches together and forms two new cells. This process is not really considered part of mitosis and occurs to just split the cells off into two separate entities.

Apoptosis

Apoptosis is essentially how a cell commits suicide. However, apoptosis is a natural and clean death that results when the cell is too old or there is DNA that is damaged beyond repair. This is to help regulate the cells in order to prevent cancer cells or other malformed cells. Apoptosis can also occur as an immune response.

The chemical mechanism of apoptosis proceeds by activating digestive enzymes from within the cell. This causes the cell to destroy itself from within. When the cell lyses, certain chemicals are released along with it that attract lysosomes and macrophages to digest the cell through endocytosis.

Click here to see the differences between mitosis and meiosis.

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