““Cell Division”Cell Division”

……what is cell division?what is cell division? Cell divisionCell division is the process by which a is the process by which a parent parent

cellcell divides into two or more divides into two or more daughter cellsdaughter cells.. Cell division is usually a small segment of a Cell division is usually a small segment of a

larger larger cell cyclecell cycle

Cell division is the process that cells go Cell division is the process that cells go through in order to divide. through in order to divide.

“ “Two Types Of Cell Division”Two Types Of Cell Division” … …depending on the purpose:depending on the purpose: MITOSIS - The cell division associated with MITOSIS - The cell division associated with

growth and cell replacement or repair.growth and cell replacement or repair.

MEIOSIS - The cell division associated with MEIOSIS - The cell division associated with sexual reproduction. sexual reproduction.

Mitosis - Process of Cell DivisionMitosis - Process of Cell Division

Mitosis is the cell division process wherein the Mitosis is the cell division process wherein the eukaryotic cell splits the eukaryotic cell splits the chromosomeschromosomes (thread (thread like strands of DNA) in its cell nucleus in to like strands of DNA) in its cell nucleus in to two identical sets in two separated nuclei. The two identical sets in two separated nuclei. The process is instantly followed by cytokinesis, in process is instantly followed by cytokinesis, in which the nuclei, cytoplasm, organelles and which the nuclei, cytoplasm, organelles and cell membrane get divided into two separate cell membrane get divided into two separate cells having equal proportions of these cellular cells having equal proportions of these cellular components. components.

CytokinesisCytokinesis is the process of is the process of dividing the cytoplasm and the dividing the cytoplasm and the

cellmembrane, and this process cellmembrane, and this process may follow immediately after may follow immediately after mitosis or occur separately, mitosis or occur separately, depending on the organism depending on the organism

involved. involved.

Meiosis, on the other hand, reduces the number Meiosis, on the other hand, reduces the number of chromosomes by half, so that, for example, of chromosomes by half, so that, for example, human egg and human egg and spermsperm cells, called gametes, cells, called gametes, each have 23 chromosomes and can join to each have 23 chromosomes and can join to produce a produce a zygotezygote with 46. It has two division with 46. It has two division phases, whereas mitosis has only one. phases, whereas mitosis has only one.

““Stages Of Cell Division”Stages Of Cell Division”

Interphase:Interphase: This is the first stage of cell This is the first stage of cell division wherein the cell is engaged in division wherein the cell is engaged in metabolic activity and prepares itself for cell metabolic activity and prepares itself for cell division process. Interphase comprises of three division process. Interphase comprises of three phases, including G1, S and G2 in which the phases, including G1, S and G2 in which the cell matures by producing proteins and cell matures by producing proteins and cytoplasmic organelles. In this phase, the DNA cytoplasmic organelles. In this phase, the DNA replicates but has not yet formed a condensed replicates but has not yet formed a condensed clear structure of chromosome. clear structure of chromosome.

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

Prometaphase:Prometaphase: In prometaphase, each chromosome In prometaphase, each chromosome forms two kinetochores (protein structure on forms two kinetochores (protein structure on chromosomes) at the centromere, one attached at chromosomes) at the centromere, one attached at each chromatid. Microtubules (structural each chromatid. Microtubules (structural components of the cell) attach at the kinetochores components of the cell) attach at the kinetochores and the chromosomes start moving. and the chromosomes start moving.

Metaphase:Metaphase: The spindle fibers attach themselves to the The spindle fibers attach themselves to the centromere of the chromosomes and align them along the centromere of the chromosomes and align them along the middle of the cell nucleus. The line is referred as the equatorial middle of the cell nucleus. The line is referred as the equatorial plate or metaphase plate. This alignment will ensure that in the plate or metaphase plate. This alignment will ensure that in the next phase, when the chromosomes will separate, each newly next phase, when the chromosomes will separate, each newly formed nucleus will get one copy of each chromosome.formed nucleus will get one copy of each chromosome.

Anaphase:Anaphase: In this phase, as the spindle fiber shorten and the In this phase, as the spindle fiber shorten and the centromere splits, the paired chromosomes will separate and centromere splits, the paired chromosomes will separate and start moving to the opposite sides of the cell. Though the reason start moving to the opposite sides of the cell. Though the reason for this motion is still unknown, according to some studies, it is for this motion is still unknown, according to some studies, it is the rapid assembly and breakdown of microtubules that may the rapid assembly and breakdown of microtubules that may cause this movement. Hence, at the end of anaphase, we get two cause this movement. Hence, at the end of anaphase, we get two separate identical copies of sister chromosomes.separate identical copies of sister chromosomes.

Telophase:Telophase: In telophase, the sister chromosomes In telophase, the sister chromosomes attach at the opposite ends of the pole and a new attach at the opposite ends of the pole and a new nuclear membrane is formed around each set of sister nuclear membrane is formed around each set of sister chromosomes. The spindle fibers also disintegrate.chromosomes. The spindle fibers also disintegrate.

Cytokinesis:Cytokinesis: Though not a phase of mitosis, Though not a phase of mitosis, cytokinesis is a separate process that completes the cytokinesis is a separate process that completes the entire process of cell division. It is a process of entire process of cell division. It is a process of splitting the daughter cells apart by forming a furrow splitting the daughter cells apart by forming a furrow wherein the cell is pinched in to two. By the end of wherein the cell is pinched in to two. By the end of this process, each daughter cell has a complete copy this process, each daughter cell has a complete copy of the genome of its parent cell, i.e. same number and of the genome of its parent cell, i.e. same number and quality of chromosomes.quality of chromosomes.

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… …by perezjohnvby perezjohnv