Cell Division In Eukaryotes

In eukaryotic cell division, both the cytoplasm and the nucleus divide. There are two kinds of cell division in eukaryotes. The first type of cell division that you will learn about is called mitosis. Mitosis results in new cells with genetic material that is identical to the genetic material of the original cell. Mitosis occurs in organisms undergoing growth, development, repair, or asexual reproduction. Asexual reproduction is the production of offspring from one parent.

The second type of cell division that you will learn about (in the next section) is called meiosis. Meiosis occurs during the formation of gametes, which are hap-loid reproductive cells. Meiosis reduces the chromosome number by half in new cells. Each new cell has the potential to join with another haploid cell to produce a diploid cell with a complete set of chromosomes.

The Cell Cycle

The cell cycle is the repeating set of events in the life of a cell. Cell division is one phase of the cycle. The time between cell divisions is called interphase. Interphase is divided into three phases, and cell division is divided into two phases, as shown in Figure 8-5.

During cell division, the chromosomes and cytoplasm are equally divided between two offspring cells. Cell division consists of mitosis and cytokinesis. During mitosis, the nucleus of a cell divides. Cytokinesis is the division of the cell's cytoplasm.

Interphase

Notice in Figure 8-5 that cells spend most of the cell cycle in interphase. Following cell division, offspring cells are approximately half the size of the original cell. During the first stage of inter-phase—called the Gj phase—offspring cells grow to mature size. G1 stands for the time gap following cell division and preceding DNA replication. After cells have reached a mature size, many proceed into the next phase of interphase, called the S phase. During the S phase, the cell's DNA is copied (synthesized). The G2 phase represents the time gap following DNA synthesis (S phase) and preceding cell division. The G2 phase is a time during which the cell prepares for cell division.

Cells can also exit the cell cycle (usually from the G1 phase) and enter into a state called the G0 phase. During the G0 phase, cells do not copy their DNA and do not prepare for cell division. Many cells in the human body are in the G0 phase. For example, fully developed cells in the central nervous system stop dividing at maturity and normally never divide again.

(DNA is copied)

Ano Ang Bullying

(DNA is copied)

figure 8-5

(growth and preparation for cell division)

(growth and preparation for cell division)

The cell cycle consists of interphase and cell division. Phases of growth, DNA synthesis, and preparation for cell division make up interphase. Cell division is divided into mitosis (division of the nucleus) and cytokinesis (division of the cytoplasm).

figure 8-5

The cell cycle consists of interphase and cell division. Phases of growth, DNA synthesis, and preparation for cell division make up interphase. Cell division is divided into mitosis (division of the nucleus) and cytokinesis (division of the cytoplasm).

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www.scilinks.org Topic: Cell Cycle Keyword: HM60235

Early mitotic Centrosome spindle

(with centrioles)

Early mitotic Centrosome spindle

(with centrioles)

Nuclear membrane

Chromatids 0 PROPHASE

Polar fibers

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