Cell Division

Division of the Cell C hapter 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 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 Cell Page 244 Some eukaryotic cells divide 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 undergo mitosis and 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 most can never be replaced; 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.

Ratio of surface area to volume (Page 243)

Cell Cycle

Before cell division occurs, the cell replicates or copies its entire DNA. DNA replication occurs during the S phase of Interphase. Each daughter cell gets one complete set of genetic information. This division of the genetic material is called mitosis. Division of the Cell

Mitosis 9QB0 9QB0

Mitosis Mitosis has four phases: Prophase Metaphase Anaphase Telophase

Prophase -First and longest phase of mitosis. During prophase: the chromatin condenses into chromosomes, the centrioles separate and spindles begin to form, and the nuclear envelope breaks down / ocs/us/common/dorlands/dorland/image s/mitosis(1).jpg

Metaphase -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 / ocs/us/common/dorlands/dorland/image s/mitosis(1).jpg

Anaphase -Third phase of mitosis. During anaphase: the chomosomes separate into individual chromatids and are moved apart to each end of the cell / ocs/us/common/dorlands/dorland/image s/mitosis(1).jpg

Telophase -Fourth and final phase of mitosis. During telophase: the chromatids gather at opposite ends of the cell and become less distinct, and two new nuclear envelopes begin to form. s/mitosis(1).jpg

Cytokinesis The nucleus has divided, mitosis is over and all that now remains to complete cell division is the division of the cell itself, a phase called cytokinesis. This phase occurs after telophase and is not part of mitosis. (Mitosis involves the division of the chromosomes in the nucleus.)

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

Cytokinesis In 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. Cell Plate

Cytokinesis In 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. s/mitosis(1).jpg

Mitosis Review