Cell Cycle/Mitosis -Notes- LIMITS TO CELL GROWTH The a cell becomes, the more demands the cell places on DNA. Additionally, the cell has more trouble moving enough and wastes across the cell membrane. DIVISION OF THE CELL Before a cell becomes too large, it undergoes, in which the cell divides and becomes 2 daughter cells. Before cell division occurs, the cell replicates all of its. Each daughter cell then receives its own copy of DNA, or genetic information. Each daughter cell has an increased ratio of which allows for sufficient exchange of materials with the environment.
CELL DIVISION In eukaryotes, cell division occurs in 2 main stages: o - the first stage- division of the cell nucleus. o - the second stage- division of the cytoplasm Many organisms, particularly unicellular organisms, reproduce via mitosis and cytokinesis. This is a form of, 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 o Humans have chromosomes, or pairs of chromosomes. Before cell division, chromosomes are replicated and form two identical 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, near the middle of the chromatid.
CELL CYCLE The Cell Cycle- During the cell cycle, a cell grows, prepares for division, and divides to form daughter cells, each of which begins the cell cycle again. Consists of 4 phases: o M Phase- includes and. o S Phase- chromosome replication, synthesis of occurs o G1 cells do most of their. In this phase, cells increase in size and synthesize new proteins and organelles. o G2 the 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. MITOSIS Prophase- first and longest phase (~50-60%) of mitosis. o Chromosomes become visible. Centrioles separate and move toward. o Centrioles lie within the and helps organize the spindle which works to separate the chromosomes. o Near the end of prophase, the begins to break down.
Metaphase- chromosomes line up across the of the cell. o Microtubules connect the of each chromosome to the two poles of the spindle. Anaphase- the centromeres that join the sister chromatids split, allowing the sister chromatids to separate and become individual. Anaphase ends when chromosomes reach opposite poles and stop. Telophase- final phase of mitosis o Nuclear envelope re-forms, spindle breaks apart, and nucleus becomes. Cytokinesis- Cytoplasm divides. Cytokinesis typically occurs simultaneously with. Each part now contains its own nucleus, DNA, and cell organelles. In plants, a forms between the divided nuclei and gradually develops into a separating membrane.
REGULATING THE CELL CYCLE Different types of cells go through the cell cycle at different. Experiments show that normal cells will reproduce until o When cells come into contact with other cells, they respond by. This is called. o 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 which increases and decrease during the cell cycle. 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. Cell Regulation: proteins that respond to events outside the cell. Direct cells to speed up or slow down the cell cycle. (ie: growth factors)
UNCONTROLLED CEL GROWTH Cancer- o 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 that can damage the surrounding tissues. - cancer cells typically remain clustered together and are relatively harmless. - cancer cells break away and metastasize from the tumor. These can be carried elsewhere in the body. - substances known to promote the development of cancer.