Cell Division. Division of the Cell C hapter 10 When a living thing grows, what happens to its...

Cell Division

Division of the CellChapter 10

When a living thing grows, what happens to its cells?

Does an animal get larger because its cells increase in size or because it produces more of them?

When a somatic cell divides, it forms two identical “daughter cells”. The process by which a cell divides into two new daughter cells is called cell division.

Division of the CellPage 244

Some eukaryotic cell divides for growth, development, and repair of the organism…but not all somatic cells undergo mitosis and those that do, do so at different rates (see page 249 in your text).

Skin cells continuously divide, so that our skin is constantly renewed and repaired.

Heart cells and many nerve cells stop undergoing mitosis soon after birth. (Caution: overconsumption of alcohol can kill nerve/brain cells, and it is believed that they can never be replaced; that they will never “grow back.”).

Liver cells are somewhere in between. In a healthy adult, liver cells normally do not divide. Where there is minor liver damage liver cells can and do divide to repair the damage. Major liver damage or advanced cirrhosis is too much damage to be repaired through mitosis. It is though, possible to use one adult liver to do liver transplants for four babies, and if all goes well, these pieces will eventually regenerate whole livers.

Cell Growth (p. 341)

Cells that do divide, grow larger.

They cannot just keep growing indefinitely because the larger the cell,- the more demands are placed on its DNA- the more trouble it has moving enough nutrients and wastes across the cell membrane.

Ratio of surface area to volume(Page 243)

Remember that before cell division occurs, the cell replicates or copies its entire DNA. DNA replication occurs during a phase in the cell cycle called Interphase.

Each daughter cell gets one complete set of genetic information. This division of the genetic material is called mitosis.

Division of the Cell

Cell Cycle

http://stevebambas.com/images/03_30CellCycle-L.jpg

The cell cycle has 6 phases:

• Interphase (which has 3 subphases: G1, S, G2) • Prophase }• Metaphase } All 4 are phases of

mitosis• Anaphase }• Telophase }• Cytokinesis

Mitosis

Mitosis has four phases: • Prophase•Metaphase• Anaphase• Telophase

ProphaseFirst and longest phase of mitosis. During prophase:• the chromatin

condenses into chromosomes,• the centrioles separate

and a spindle begins to form, and• the nuclear envelope

breaks down.

http://a248.e.akamai.net/7/248/430/20080327144033/www.mercksource.com/ppdocs/us/common/dorlands/dorland/images/mitosis(1).jpg

MetaphaseThe second phase of mitosis. During metaphase:• the chromosomes line

up across the center of the cell, and• each chromosome is

connected to a spindle fiber at its centromere.


Anaphase

The third phase of mitosis. During anaphase, the sister chromatids separate into individual chromosomes and are moved apart.


TelophaseThe fourth and final phase of mitosis. During telophase:• the chromosomes gather at opposite ends of

the cell and become less distinct, and• two new nuclear envelopes begin to form.


Cytokinesis

All that now remains to complete cell division is the division of the cytoplasm itself, a phase called cytokinesis. This phase occurs after telophase.

Cytokinesis takes place in different ways, depending on whether the cell is an animal cell or a plant cell.

CytokinesisIn plant cells, a structure known as the cell plate forms midway between the divided nuclei. This cell plate gradually develops into a membrane, separating the two daughter cells. A cell wall then begins to develop in this membrane.

http://www.vcbio.science.ru.nl/images/cellcycle/mito_bellevalia_cytokinesis.jpg

Cell Plate

CytokinesisIn animal cells, the cell membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts. In both animal and plant cells, each identical daughter cell contains its own nucleus and cytoplasmic organelles.


CytokinesisIn plant cells, a structure known as the cell plate forms midway between the divided nuclei. This cell plate gradually develops into a membrane, separating the two daughter cells. A cell wall then begins to develop in this membrane.

http://www.vcbio.science.ru.nl/images/cellcycle/mito_bellevalia_cytokinesis.jpg

Cell Plate

SummaryProphase Metaphase Anaphase Telophase Cytokinesis

Stage of mitosis

1 2 3 4 Immediately following mitosis

Number of cells

1 1 1 1 2

Nuclear envelope

Breaking down

None None Reforming Established

Sister chromatids

Together Together Separating Divided Divided

Mitosis Video

http://vimeo.com/8333643



Cell Division. Division of the Cell C hapter 10 When a living thing grows, what happens to its...

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