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Why are cells so small and how do they grow?

Why are cells so small and how do they grow?. AKA: surface area to volume ratios and mitosis. Why not grow BIGGER?. Cells usu. Do not grow indefinitely bigger 1st reason: high demand on DNA, “DNA” overload

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Why are cells so small and how do they grow?

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  1. Why are cells so small and how do they grow? AKA: surface area to volume ratios and mitosis

  2. Why not grow BIGGER? • Cells usu. Do not grow indefinitely bigger • 1st reason: high demand on DNA, “DNA” overload • Ex: public library with 1000 books serves 2,000 people. Population increases to 10,000 people, wait lists… • 2nd reason: difficult moving nutrients/waste across cell membrane/exchanging material • Surface area to volume, volume increase and surface area does not keep pace • Ex: Town has a 2 lane main street, population jumps from 2,000 to 10,000…congestion moving things in and out.

  3. Division of the cell • Before a cell becomes too large, forms daughter cells • 1 cell = 1 daughter cells; cell division • First what has to happen? - DNA replication, need another copy of the DNA; • G 1 phase • S phase • G 2 phase • Mitosis • Cytokinesis

  4. Cell Cycle

  5. Mitosis: prophase • Interphase: cell growth G1, DNA replication S phase, G2 preparation for mitosis • Cell Division • Prophase: chromatin chromosomes, centrioles separate, spindle forms, paired up in chromatids • Pro= before/start

  6. Mitosis: metaphase (meta=middle) • Metaphase: Chromosomes line up in middle, spindle fiber connected to centromere • Meta=middle

  7. Mitosis: anaphase • Anaphase: sister chromatids separate into individual chromosomes and are moved apart • Ana=apart

  8. Mitosis: telophase Telophase: chromosomes gather at opposite ends, new nuclear envelopes will form. Cleavage furrow forms-animal cells, pinch apart Cell plate- plant cells forms in middle and pushes apart

  9. Mitosis is done, Now comes… • Cytokinesis: Cytoplasm splits; cytoplasm pinches in half, each daughter cell as an identical set of duplicate chromosomes

  10. What do you remember? • Chromatin • Centrioles • Chromosomes • Sister Chromatid • Individual chromosomes • Centromere • Spindle fiber • Nuclear envelope • Cleavage furrow • Cell plate

  11. Chromatin • Centrioles • Chromosomes • Sister Chromatid • Individual chromosomes • Centromere • Spindle fiber • Nuclear envelope • Cleavage furrow • Cell plate • DNA, unwound with proteins • In cyto, holds onto the spindle fiber • Condensed package of DNA • Pairs of duplicated chromosomes • Located in the middle of the sister chromatids, spindle fiber attaches here • Fan like microtubule structure that helps to separate the chromosomes • Dissolves to allow mitosis to begin • The cell membrane pinches in during telophase • The cell plate/wall forms and pushes the plant cells apart

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  15. Regulating the Cell Cycle • Controls on cell division: • Proximity • IInjury • Cyclin- a protein that tells cells to enter the cell cycle • Cell Cycle regulators • Internal regulators: proteins assure that the previous steps have been completed. Ex: protein that checks that the spindle fiber has attached before anaphase continues • External regulators: proteins outside cell speed up/slow down cell cycle. Ex: growth factors that aid in healing

  16. Uncontrolled Cell Growth • Cancer: a 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 • As a result they divide uncontrollably; cell cycle is broken down • Many cancers have a defect at gene p53 = causes cells to lose info needed to respond to signals that would control growth

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