Cell Growth and Division. Cell Growth Limits to growth –Stress on DNA –Difficulty moving...
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Transcript of Cell Growth and Division. Cell Growth Limits to growth –Stress on DNA –Difficulty moving...
![Page 1: Cell Growth and Division. Cell Growth Limits to growth –Stress on DNA –Difficulty moving nutrients/wastes across membrane Ratio of surface area to volume.](https://reader035.fdocuments.in/reader035/viewer/2022062717/56649e545503460f94b4b7d6/html5/thumbnails/1.jpg)
Cell Growth and Division
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Cell Growth• Limits to growth– Stress on DNA – Difficulty moving nutrients/wastes
across membrane• Ratio of surface area to volume• Volume increases at a faster rate than
surface area
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Cell Division
• Before a cell becomes too large, it divides, producing 2 daughter cells– Each daughter cell is an exact replica of the
parent cell
• Before the cell divides, the DNA is replicated, so each new cell will have the same genetic information as the parent cell
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Cell Division
• 2 stages (eukaryotes)– Mitosis- division of the cell nucleus– Cytokinesis- division of the cytoplasm
• Asexual reproduction (esp for unicellular organisms)
• Also used for new cells as an organism grows and develops
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Chromosomes
• Threadlike structure within the nucleus containing the genetic information (DNA) that is passed from one generation of cells to the next
• Cells of every organism have a specific number of chromosomes– Fruit flies = 8; Humans = 46; carrots = 18
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Chromosomes
• Chromatin- granular material visible within the nucleus; consists of DNA tightly coiled around proteins
• Chromatid- one of two identical “sister” parts of a duplicated chromosome
• Centromere- an area where the chromatids are attached to one another
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The Cell Cycle
• 2 major phases– Interphase– Mitosis
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Interphase
• 3 phases– G1 phase= cells do most
of their growing• Increase in size and
synthesize new proteins and organelles
– S phase= chromosomes are replicated and the synthesis and DNA molecules takes place
• Usually if a cell enters S phase and begins replication, it completes the rest of the cycle
– G2 phase= many of the organelles and molecules required for cell division are produced
• Shortest of the 3 phases of interphase
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Mitosis
• Divided into 4 phases– Prophase– Metaphase– Anaphase– Telophase
• Followed with Cytokinesis
• Depending on cell- may last a few minutes to several days
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Prophase• 1st and longest phase
of mitosis• Events
– Chromosomes become visible– Centrioles separate and move to opposite sides
of the cell– Chromosomes become attached to fibers in the
spindle at the centromere– Chromosomes coil more tightly– Nucleolus disappears – Nuclear envelope breaks down
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Metaphase• Often lasts only a
few minutes
• Events– Chromosomes line
up across the center of the cell
– Microtubules connect the centromere of each chromosome to the two poles of the spindle
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Anaphase
• Centromeres split
• Sister chromatids separate and move to opposite poles
• Anaphase ends when chromosomes stop moving
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Telophase
• Chromosomes begin to disperse into a chromatin
• Nuclear envelope re-forms around each cluster of chromosomes
• Spindle begins to break apart
• Nucleolus becomes visible
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Cytokinesis
• Occurs at the same time as telophase
• Animal cells:– Cell membrane is drawn inward
until the cytoplasm is pinched into 2 nearly equal parts
• Plant cells:– Cell plate forms midway between
the divided nuclei– Cell wall begins to appear in the
cell plate
• Result? 2 new identical cells
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Controls on Cell Division
• Effects of controlled cell growth can be seen by placing some cells in a petri dish containing nutrient broth
• Cells grow until they form a thin layer covering the bottom of the dish
• Cells stop growing when they come into contact with other cells
• If cells are removed, the remaining cells will begin dividing again
• Something can turn cell division on or off
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Regulating Cell Growth
• Cyclins- proteins that regulate the timing of the cell cycle in eukaryotic cells– Internal regulators: proteins that respond to
events inside the cell• i.e. make sure all chromosomes have been
replicated; make sure all chromosomes are attached to the spindle before entering anaphase
– External regulators: proteins that respond to events outside the cell
• i.e. embryonic development; wound healing
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Uncontrolled Cell Growth
• Cancer- disorder in which some of the body’s own cells lose the ability to control growth
• Cancer cells do not respond to the signals that regulate the growth of most cells
• P53 gene halts the cell cycle until all chromosomes have been properly replicated– A damaged or defective p53 gene causes the cells to
lose the information needed to respond to signals that would normally control their growth