Cell Division
Most cells of the human body undergo cell division, the process by which cells reproduce
themselves. There are two types of cell division:
1. Somatic cell division
2. Reproductive cell division
A somatic cell (so¯-MAT-ik; soma body) is any cell of the body other than a germ cell.
A germ cell is a gamete (sperm or oocyte) or any precursor cell destined to become a gamete.
Somatic cell division, a cell undergoes a nuclear division called mitosis and a cytoplasmic division
called cytokinesis to produce two genetically identical cells, each with the same number and kind of
chromosomes as the original cell.
Eg: Somatic cell division replaces dead or injured cells and adds new ones during tissue growth.
Reproductive cell division is the mechanism that produces gametes, the cells needed to form the next
generation of sexually reproducing organisms. This process consists of a special two step division called
meiosis, in which the number of chromosomes in the nucleus is reduced by half.
Somatic Cell Division
The cell cycle is an orderly sequence of events in which a somatic cell duplicates its
contents and divides in two.
The cell cycle consists of two major periods:
1. Interphase: cell is not dividing
2. Mitotic (M) phase: cell is dividing
1. Interphase
During interphase the cell replicates its DNA. Interphase is a state of high metabolic activity; it is
during this time that the cell does most of its growing.
Interphase consists of three phases: G1, S, and G2
S-phase: S stands for synthesis of DNA. The S phase, the interval between G1 and G2, lasts about
8 hours. During the S phase, DNA replication occurs. As a result of DNA replication, the two identical
cells formed during cell division later in the cell cycle will have the same genetic.
G1- Phase: The G1 phase is the interval between the mitotic phase and the S phase. During G1, the cell
is metabolically active; it replicates most of its organelles and cytosolic components but not its DNA.
Replication of centrosomes also begins in the G1 phase. G1 lasts 8 to 10 hours.
G0 -Phase: Exit from cell cycle (nondividing cell)
, G2 -Phase: The G2 phase is the interval between the S phase and the mitotic phase. It lasts 4 to 6 hours.
During G2, cell growth continues, enzymes and other proteins are synthesized in preparation for cell
division, and replication of centrosomes is completed.
Once a cell completes its activities during the G1, S, and G2 phases of interphase, the mitotic phase
begins.
2. Mitotic Phase
The mitotic (M) phase of the cell cycle, which results in the formation of two identical cells, consists
of a nuclear division (mitosis) and a cytoplasmic division (cytokinesis) to form two identical cells.
Nuclear Division: Mitosis, as noted earlier, is the distribution of two sets of chromosomes into two
separate nuclei. The process results in the exact partitioning of genetic information. The mitosis
involves 4 different stages:
• Prophase
• Metaphase
• Anaphase
• Telophase
1. Prophase
In early prophase:
• The chromosomes start to condense (making them easier to pull apart later on).
• The mitotic spindle begins to form. The spindle is a structure made of microtubules, strong
fibers that are part of the cell’s “skeleton.” Its job is to organize the chromosomes and move
them around during mitosis. The spindle grows between the centrosomes as they move apart.
• The nucleolus (or nucleoli, plural), a part of the nucleus where ribosomes are made,
disappears. This is a sign that the nucleus is getting ready to break down.
In late prophase (sometimes also called prometaphase), the mitotic spindle begins to capture and
organize the chromosomes.
• The chromosomes become even more condensed, so they are very compact.
• The nuclear envelope breaks down, releasing the chromosomes.
Most cells of the human body undergo cell division, the process by which cells reproduce
themselves. There are two types of cell division:
1. Somatic cell division
2. Reproductive cell division
A somatic cell (so¯-MAT-ik; soma body) is any cell of the body other than a germ cell.
A germ cell is a gamete (sperm or oocyte) or any precursor cell destined to become a gamete.
Somatic cell division, a cell undergoes a nuclear division called mitosis and a cytoplasmic division
called cytokinesis to produce two genetically identical cells, each with the same number and kind of
chromosomes as the original cell.
Eg: Somatic cell division replaces dead or injured cells and adds new ones during tissue growth.
Reproductive cell division is the mechanism that produces gametes, the cells needed to form the next
generation of sexually reproducing organisms. This process consists of a special two step division called
meiosis, in which the number of chromosomes in the nucleus is reduced by half.
Somatic Cell Division
The cell cycle is an orderly sequence of events in which a somatic cell duplicates its
contents and divides in two.
The cell cycle consists of two major periods:
1. Interphase: cell is not dividing
2. Mitotic (M) phase: cell is dividing
1. Interphase
During interphase the cell replicates its DNA. Interphase is a state of high metabolic activity; it is
during this time that the cell does most of its growing.
Interphase consists of three phases: G1, S, and G2
S-phase: S stands for synthesis of DNA. The S phase, the interval between G1 and G2, lasts about
8 hours. During the S phase, DNA replication occurs. As a result of DNA replication, the two identical
cells formed during cell division later in the cell cycle will have the same genetic.
G1- Phase: The G1 phase is the interval between the mitotic phase and the S phase. During G1, the cell
is metabolically active; it replicates most of its organelles and cytosolic components but not its DNA.
Replication of centrosomes also begins in the G1 phase. G1 lasts 8 to 10 hours.
G0 -Phase: Exit from cell cycle (nondividing cell)
, G2 -Phase: The G2 phase is the interval between the S phase and the mitotic phase. It lasts 4 to 6 hours.
During G2, cell growth continues, enzymes and other proteins are synthesized in preparation for cell
division, and replication of centrosomes is completed.
Once a cell completes its activities during the G1, S, and G2 phases of interphase, the mitotic phase
begins.
2. Mitotic Phase
The mitotic (M) phase of the cell cycle, which results in the formation of two identical cells, consists
of a nuclear division (mitosis) and a cytoplasmic division (cytokinesis) to form two identical cells.
Nuclear Division: Mitosis, as noted earlier, is the distribution of two sets of chromosomes into two
separate nuclei. The process results in the exact partitioning of genetic information. The mitosis
involves 4 different stages:
• Prophase
• Metaphase
• Anaphase
• Telophase
1. Prophase
In early prophase:
• The chromosomes start to condense (making them easier to pull apart later on).
• The mitotic spindle begins to form. The spindle is a structure made of microtubules, strong
fibers that are part of the cell’s “skeleton.” Its job is to organize the chromosomes and move
them around during mitosis. The spindle grows between the centrosomes as they move apart.
• The nucleolus (or nucleoli, plural), a part of the nucleus where ribosomes are made,
disappears. This is a sign that the nucleus is getting ready to break down.
In late prophase (sometimes also called prometaphase), the mitotic spindle begins to capture and
organize the chromosomes.
• The chromosomes become even more condensed, so they are very compact.
• The nuclear envelope breaks down, releasing the chromosomes.
