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Cell Division Chapter 10 Anatomy of a Chromosome coils of DNA and proteins Centromerewhere the two chromatids attach Chromatid- two exact copies of DNA that make up a chromosome Limits to Cell Growth • DNA Overload – The larger a cell becomes, the more demands the cell places on its DNA • Exchanging Material – The cell has trouble moving enough nutrients and wastes across the cell membrane if the cell is too big. – Surface Area:Volume ratio can’t be too small Cell Cycle • Interphase (inter- means “between”) – G1 phase – Cell growth – S phase – DNA replication – G2 phase – preparation for cell division – Cells are in interphase most of the time. • M phase – Mitosis: prophase, metaphase, anaphase, telophase, cytokinesis • G0 phase – Cells that cannot divide like nerve cells, red blood cells, and cardiac cells Prophase A? • What are the important events happening during Prophase? Plant cells in prophase Pair of centrioles B? C? D? Plant cells in prophase Prophase • Chromosomes condense into sister chromatids • Chromatids are joined by a centromere • Centrioles appear and form mitotic spindle • Nucleolus disappears and nuclear envelope dissolves • Longest phase of mitosis (50-60%) Pair of centrioles Metaphase Animal cell Plant cell A? B? C? D? • What events are occurring during Metaphase? Metaphase Animal cell Plant cell • Centrioles on opposite ends of the cell • Microtubules of mitotic spindle attach to the centromeres • Chromosomes line up across the middle (equator) of the cell Anaphase • What important events are occurring at Anaphase? A? B? Early anaphase (plant) C? D? Anaphase (animal) Late anaphase (plant) Anaphase Early anaphase (plant) • Sister chromatids separate • Chromosomes migrate to opposite ends of the cell Anaphase (animal) Late anaphase (plant) Telophase Plant cell Animal cell • What important events happen during Telophase? A? B? C? D? Telophase Plant cell Animal cell • Chromosomes begin to disperse • Nuclear envelopes reform • Mitotic spindle breaks apart Animal cell Cytokinesis Plant cell • Difficult to distinguish from telophase • In animal cells the cell membrane pinches in forming two daughter cells • In plant cells a cell plate forms between the daughter nuclei and a new cell wall forms at the cell plate Which stage is each photo in?? How do you know?? Now its YOUR turn! What are the important events at each phase? G1 phase –?? S phase –?? G2 phase –?? What types of cells would be in G0 phase?? Cancer • Uncontrolled cell growth – Caused by smoking, exposure to radiation or certain chemicals, some viruses • Cancer cells smother normal cells • Treatment options – Surgery to remove tumor – Radiation therapy to halt cell division – Chemotherapy to halt cell division