Cell Growth and Division Chapter 10
Cell Division Before a cell becomes too large, it undergoes cell division, in which the cell divides and becomes 2 daughter cells. Before cell division occurs, the cell replicates all of its DNA. Each daughter cell then receives its own copy of DNA, or genetic information. Each daughter cell has an increased ratio of surface area to volume which allows for sufficient exchange of materials with the environment.
Cell Division In eukaryotes, cell division occurs in 2 main stages: Mitosis- the first stage Cytokinesis- the second stage- division of the cytoplasm Many organisms, particularly unicellular organisms, reproduce via mitosis and cytokinesis. This is a form of asexual reproduction, since the cells produced by mitosis are genetically identical to the parent cell. Mitosis is also the source of new cells when a multicellular organism grows and develops.
Chromosomes Chromosomes carry the genetic information of an individual organism, and are responsible for passing genetic information between generations. Organisms have a characteristic number of chromosomes Humans have 23 pairs or 46 chromosomes. Before cell division, chromosomes are replicated and form two identical sister chromatids. When the cell divides, the sister chromatids separate from each other. One chromatid goes to each of the two new cells. Each pair of chromatids is attached at the centromere, near the middle of the chromatid. Centromere Sister Chromatids
Interphase The Cell Cycle The Cell Cycle- a series of events that cells go through. During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells, each of which begins the cell cycle again. Consists of 4 phases M Phase- includes mitosis and cytokinesis S Phase- chromosome replication, synthesis of DNA occurs G 1 cells do most of their growing. In this phase, cells increase in size and synthesize new proteins and organelles. G 2 the shortest phase of interphase, organelles and molecules required for cell division are produced. At the end of this phase, the cell is ready to enter the M phase and begin cell division.
The Cell Cycle M Phase
4 Phases of Mitosis Prophase- first and longest phase (~50-60%) of mitosis. Chromosomes become visible. Centrioles separate and move toward poles. Centrioles lie within The centrosome and helps organize the spindle which works to separate the chromosomes. Near the end of prophase, the nuclear envelope begins to break down. Centriole Spindle forming
4 Phases of Mitosis Metaphase- chromosomes line up across the middle of the cell. Microtubules connect the centromere of each chromosome to the two poles of the spindle. Microtubules connect to centromere of chromosome.
4 Phases of Mitosis Anaphase- the centromeres that join the sister chromatids split, allowing the sister chromatids to separate and become individual chromosomes. Anaphase ends when chromosomes reach opposite poles and stop moving. New individual chromosomesformed from sister chromatids
4 Phases of Mitosis Telophase- final phase of mitosis- nuclear envelope re-forms, spindle breaks apart, and nucleus becomes visible.
Cytokinesis Cytokinesis- Cytoplasm divides. Cytokinesis typically occurs simultaneously with telophase. Each part now contains its own nucleus, DNA, and cell organelles. In plants, a cell plate forms between the divided nuclei and gradually develops into a separating membrane.
Binary Fission Binary Fissioncells grow to double their size and divide to form two cells. Occurs in prokaryotes and single celled eukaryotes. Single celled eukaryotes must still go through mitosis prior to division.
Exit Slip Name in order the stages of the cell cycle, beginning with the G 1 phase.
Warm Up Exercise When you came in, you picked up a bag with 7 images from the cell cycle. Place the images in order as best you can, then compare with a partner. Once you have reached a consensus, write the letters on your warm up sheet, and label each phase. Finally, explain what happens during that specific phase of cell division.
Regulating the Cell Cycle Different types of cells go through the cell cycle at different rates. Experiments show that normal cells will reproduce until they come into contact with other cells. When cells come into contact with other cells, they respond by not growing. This is called contact inhibition. This demonstrates that controls on cell growth and division can be turned on and off.
Contact Inhibition
Cell Cycle Regulators Cells in mitosis are regulated by a series of proteins called cyclins which increases and decrease during the cell cycle. Internal Cell Regulation: proteins that respond to events inside the cell. Allow the cell cycle to proceed only when certain processes have happened inside the cell. External Cell Regulation: proteins that respond to events outside the cell. Direct cells to speed up or slow down the cell cycle. (ie: growth factors)
Cyclins A sample of cytoplasm is removed from a cell in mitosis. The sample is injected into a second cell in G 2 of interphase. As a result, the second cell enters mitosis.
Uncontrolled Cell Growth Cancer- a disorder in which some of the body s own cells lose the ability to control cell growth. Cancer cells do not respond to the signals that regulate the growth of most cells. As a result, these cells divide uncontrollably and form masses of cells called tumors that can damage the surrounding tissues.
Uncontrolled Cell Growth Benign- cancer cells typically remain clustered together and are relatively harmless. Malignant- cancer cells break away and metastasize from the tumor. These can be carried elsewhere in the body. Carcinogens- substances known to promote the development of cancer.
Cancer/Stem Cell Discussion Reading on pg. 253 BioDetectives video- Skin Cancer: Deadly Cells
Exit Slip Anticancer drugs prevent microtubules from forming spindle fibers. Why do you think these drugs might be effective treatments for cancer?