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Cell Growth & Division Do now: Who has bigger cells? Do Now: Which has larger cells, a mouse or an elephant? CELLS ARE SMALL! Why do we need to make more cells? From One Cell to Many Sea Urchin Cell Division Why do we need to make more cells? Why are we one hundred trillion SMALL cells and not one hundred LARGE cells? 100,000,000,000,000 cells because.... I. Why do Cells Divide? A. Cells need to stay small because: – The larger a cell becomes, the more demands on its DNA – Better organization – Needs to move nutrients and wastes across the cell membrane quickly – If too big, cannot get nutrients fast enough • DNA is the cell’s “library” of information. • Imagine a very large city using one local library for all materials A big bag is weaker, harder to find things Large cell, difficult to maneuver organelles More volume = bigger need The larger the volume of the balloon, the weaker it is. The balloon skin stays the same. B. What is Surface area? The total area of the surface of a 3D object What is the surface area of this cube? 2 cm 2 cm 24 cm2 *Large surface area SPEEDS UP the movement of materials* C. What is Volume? The amount of 3-D space that an object occupies, “capacity” *Large volume SLOWS down movement of materials* What is the VOLUME of the shape here? 200 cm3 cm • As the length of cell increases, volume increases faster surface area (cm3 compared to cm2) • HIGH ratio desired: quick movement of materials • Ex: 6000/1 is better than 2/1 It’s better to have lots of small cells instead of fewer large cells! A. All genes located in DNA in nucleus of eukaryotic cell B. Chromosomes are condensed forms of DNA C. Chromosome number is unique to every species • • • • Humans: 46 chr. Chimpanzees: 48 chr. Yeast: 32 chr. Adders-Tongue Fern: 1440 chr.! How is DNA Packaged? • Chromosome- when chromatin coils for Mitosis A. 46 chr 46 chromosomes 46 chr B. Chromosome # stays the same (Cells growths, doubles chromosomes, then splits, forming two daughter cells with original # of chromosomes) • • • • Intestinal lining- every 24 hours Skin Blood cells/bone marrow- 120 days Liver- sometimes • • • • Muscle Cells Cardiac cells Kidney Nerve cells A. Interphase: “I-ball” 90% of the time! Gap0 “resting phase”, cell is not growing Gap1 cell grows, doubles organelles Synthesis duplication of the DNA in the cell's chromosomes Gap2 cell grows, microtubules assembled Prophase- “pasta” • Chromatin fibers condense • Nuclear membrane breaks down • Spindle of microtubules forms from centrioles [animals only] • Attach to chromatids on centromere Metaphase- “middle” • Chromosomes line up in the middle • Spindle fibers attach centrioles to centromeres • Every sister chromatid has fiber attached to it Centriole Spindle Anaphase: “away phase”, form “A’s” • Spindle fibers contract • Pull sister chromatids apart • The chromosomes continue to move until they are in two groups • Each side has own copy of DNA Individual chromosomes Telophase- “end phase” • Nuclear membranes reform at each pole • Chromosomes unwind • Spindle disappears C. CYTOKINESIS During cytokinesis, the cytoplasm cuts in half A structure known as the CELL PLATE forms midway between the divided nuclei. Animal cells contract across middle of cell and “pinch” making a “cleavage furrow”. Twilight STUDIES IT TOO! Parent Cell MITOSIS Video Daughter Cells A. Spindle: network of microtubules that move chromosomes during mitosis and meiosis B. Equator: center line of cell where chromosomes line up during metaphase C. Poles: the opposite ends of cell D. Centrioles: animal cells only, move the spindle and chromosomes during division E. Centromere: region where two sister chromatids are joined tightly together A. Production of 2 new daughter cells B. Daughter cells are exactly the same as original parent cell C. Cell --> Tissue --> Organ --> Organ System --> Organism D. This is how organisms grow & develop!