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Honors Biology Cell Division Mitosis Spring 2009 • Mitosis – division process that occurs in almost all body cells • Result- from one “mother” cell, two identical “daughter” cells are produced • Uses – repair, growth, maintenance • Process divided into stages • Smooth, flowing process with each stage having early, mid and late steps Mitosis Process Interphase “Between” division stage Cell is “getting ready” to divide Doing “cell work” ** Chromosomes duplicate during this stage How many chromosomes present in a human cell? 46 What is really duplicating? How? Important Cell Parts for Interphase: Nucleus, nucleolus, centrioles, chromatin Chromosomes Chromosomes are in homologous pairs – same basic size and shape, same basic genes at same basic loci Locus = gene location Why two of each? How many pairs in a human cell? 23 pairs = 46 total Cells called Diploid when chromosomes are in pairs Duplicated Chromosomes DNA/chromosomes duplicate How? Called: Sister Chromatids Held together by a centromere Now, how many chromosomes in a human cell? 92 “Direction” on a cell Equator – center Poles – two ends Prophase Sister Chromatids thicken and become visible from chromatin Nuclear membrane and nucleolus “disappear” Centrioles duplicate and move to poles Spindle fibers grow from centrioles Still, 92 chromosomes Metaphase Sister Chromatids line up on equator in a line, two abreast Spindle fibers grow to attach to centromeres Entire set-up called the spindle Still, 92 chromosomes Anaphase Centromere splits and chromatids move to the poles Still, 92 chromosomes; 46 at each pole Telophase – Animal Cells Nucleolus and nuclear membrane reform Chromatids unravel into chromatin Spindle fibers disappear Cleavage furrow pinches the mother cell into two daughter cells Cytokinesis = final division of the cell cytoplasm How many chromosomes in each daughter cell? 46 chromosomes at each pole 2 Diploid Cells? Telophase – Plant Cells What is different about plant cells? No spindle Why not? No centrioles Cell plate grows across to divide the cells Mitosis in Summary Onion Root Tip Mitosis Onion Root Tip Cell Mitosis Onion Root Tip Mitosis Stage of Mitosis? Stage of Mitosis? Stage of Mitosis? Stage of Mitosis? Cell Cycle • Life cycle of a cell • Consists of various stages/phases Cell Cycle • • • • • • • Most of a cell’s life is spent in Interphase Mitosis is a very small part of its life Interphase divided into stages G1 occurs right after cytokinesis of mitosis G=? Growth of daughter cells occur Near the end – cellular contents (organelles, proteins, lipids, etc.) are duplicated G0 Stage • • • • • • Some cells enter from G1 to G0 Never duplicate cell organelles Never do mitosis Just become functioning cells Examples? Human muscle cells, some nervous cells, red blood cells • • • • S Phase S=? Synthesis Phase Chromatin (Chromosomes) duplicate their DNA • Chromosome number? • Goes from 46 to 92 • G2 Stage • Cells continue to grow • Chromosomes may run a “spell check” to look for errors in DNA • Can even make some repairs • • • • M phase M=? Mitosis phase Cell completes all stages of mitosis • Smallest portion of a cell’s life cycle (brown) • All in (pink/blue) = Interphase Cancer • • • • • • • • Cancer is “out of control” mitosis One mother cell may form more than two daughter cells A daughter cell may have multiple nuclei Mitosis is so rapid it often forms masses or tumors (lesions) Masses are capable of causing blood vessels to grow into them to provide blood Chemotherapy (drugs) or radiation are meant to kill cancerous (malignant) cells Often kill normal cells also = negative side effects Noncancerous tumors = benign Photos of Cancerous Tumors • Brain Cancer More Photos • Liver Cancer More Photos • Skin Cancer Photos of Cancerous Tumors Breast Cancer