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Chapter 5 Mitosis and the Cell Cycle Review. Cell Size is Limited. Cells are a certain size for a certain reason. If cells were too small , they could not contain all of the necessary organelles and molecules.
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Cell Size is Limited Cells are a certain size for a certain reason. If cells were too small, they could not contain all of the necessary organelles and molecules. If cells were too large, they could not exchange materials with the outside efficiently and there wouldn’t be enough DNA to control the cell.
Ratio of Surface Area to Volume • Large surface-to-volume ratio means the cell is too small. • Small surface-to-volume ratio mean the cell is too large. If a cell cannot move enough material through its membrane to survive, then the ratio of its surface area to volume is???
DNA Chromosomes – one long continuous thread of DNA that consists of numerous genes along with regulatory information. Each of your body cells have 46 chromosomes. Chromosomes are not visible in except during cell division.
How do chromosomes form? During the cell cycle, each of your chromosomes is associated with a group of proteins called histones. Histone – protein molecule which DNA is tightly coiled around.
Chromosomes Chromatid – one half of a duplicated chromosome. Sister Chomatids – two identical chromatids Centromere – region of the condensed chromosomes that looks pinched. Telomere – ends of the DNA molecule.
The Cell Cycle Cell Cycle– series of events that the cells go through as they grow and divide. The Cell Cycle consists of 2 main phases: Interphase – cell growth Mitosisand Cytokinesis– cell division
Interphase Interphase– the growth phase of the cell cycle. Interphase is the longest phase of the cell cycle. By the end of interphase, a cell has two full sets of DNA (chromosomes) and is large enough to begin the division process.
Phases of Interphase Interphase is divided into 3 phases: G1 (gap 1) phase - cell grows & makes proteins / organelles. S (synthesis) phase - chromosomes replicate to form identical sister chromatids held together by a centromere. G2 (gap 2) phase - continue to grow & make proteins necessary for cell division.
Mitosis Mitosis – cell division One cell becomes two cells in this phase Each cell has to have its own cytoplasm and DNA. The four strands of DNA (two sister chromatids) have to break apart so that each new cell only has one double-stranded chromosome. Mitosis is divided into 4 phases: Prophase Metaphase Anaphase Telophase
Mitosis and Cytokensis Cytokensis
Prophase Chromosomes condense & are more visible. The nuclear membrane (envelope) disappears. The centrioleshave separated and taken positions on the opposite poles of the cell. Spindle fibers form and radiate toward the center of the cell. Metaphase Chromosomes line up across the middle of the cell. Spindle fibers connect the centromere of each sister chromatid to the poles of the cell.
Anaphase Centromeres that join the sister chromatids split. Sister chromatids separate becoming individual chromosomes. Separated chromatids move to opposite poles of the cell. Telophase • Chromosomes uncoil. • A nuclear envelope forms around the chromosomes at each pole of the cell. • Spindle fibers break down and dissolve. • Cytokinesis begins.
Cytokinesis- the division of the cytoplasm into two individual cells. Cytokinesis is different in plant and animal cells. Animal cells - the cell membrane forms a cleavage furrowthat eventually pinches the cell into two nearly equal parts. • Plant cells - a cell plateforms midway b/w the divided nuclei. The cell wall forms in the cell plate.
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How Often Do Cells Divide? Not all cells move through the cell cycle at the same rate. Muscle cells and nerve cells do not divide after they have developed. Skin cells, digestive cells, bone marrow cells divide rapidly every few hours.
Regulation of the Cell Cycle The cell cycle is controlled by a chemical control system that starts and stops events in the cell cycle. External Signals (Factors) – Come from outside of the cell Internal Signals (Factors) – Come from inside the cell
External Signals (Factors) Physical External Factors Cell division is turned off when cells are packed too close together. Cell division is turned on when cells are not in contact with another surface. Chemical External Factors Growth Factors – proteins that stimulate cell division by binding to receptors that activate genes to trigger cell growth.
Internal Signals (Factors) Internal Signals (Factors) come from inside the cell and include several types of molecules found in the cytoplasm. Kinase – enzyme that regulates the cell cycle Cyclins – proteins that regulate the cell cycle.
Checkpoints Checkpoint – critical point where “stop” & “go” signals can regulate the cycle. Cell division is mostly in the “off” position in animal cells when there is no stimulus present.
Apoptosis • Apoptosis- programmed cell death • Cell death is balanced by cell division which keeps body tissue from growing or shrinking as cells reach the end of their life span. • Example: webbing between toes (look in book)
Cancer Cancer – uncontrolled cell division Happens when the regulation of the cell cycle breaks down. These cells divide much more often than healthy cells do.
Tumors Tumors – disorganized clumps of cancer cells Benign – cancer cells remain clustered together. It may be harmless and easily removed. Malignant – some of the cancer cells can breakaway from the tumor & be carried to other parts of the body and form more tumors (metastasize). This is more difficult to treat.
Stem Cell Research • Stem Cells- unspecialized cells that continually reproduce and have the ability to differentiate into any cell. • Embryonic Stem Cells - have not yet differentiated into various cell types. • Adult Stem Cells - found in adult organisms in bone marrow.
