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CELL REPRODUCTION: MITOSIS Cell division • Cell reproduction: the process of one cell dividing into two cells parent cell two daughter cells • Mitosis: asexual reproduction to make new cells for organism growth or tissue repair *25 million cells undergoing mitosis each second in the human body Spontaneous Generation & the Theory of Biogenesis • The now disproved idea that living things arose from non-living things. ex: spoiled meat “growing” maggots • Disproved eventually by Louis Pasteur (see page 177-178) • The Theory of Biogenesis: all life come from life; so...all cells come from other cells Cell Division • Basics: Asexual reproduction – cells duplicate their DNA and split into two genetically identical cells ex: mitosis, budding, binary fission *all multicellular organisms perform mitosis Sexual reproduction – a combination of genetic material from two different organisms resulting in an offspring that is genetically different than the parent ex: meiosis Cell Life Cycle • Phases: 1. interphase: where the cell spends 90% of their lives 2. prophase 3. prometaphase 4. metaphase 5. anaphase 6. telophase *PPMAT = phases of mitosis (#2-6) DNA Replication • Occurs at the end of interphase • Helicase unzips the DNA strand • DNA polymerase binds to the DNA strand and creates a complementary daughter strand • This creates two new strands of DNA (p. 182) • After DNA replication the cell enters mitosis • The identical strands of DNA (which are called sister chromatids) are held together in the middle by the centromere Interphase • • • • spends most of its life (time) in this phase performs everyday vital functions DNA in the form of chromatin during the end of interphase the cell replicates the DNA (46 chromosomes becomes 92 – two exact copies of each) Prophase • the nucleoli begin to disappear • DNA condenses and becomes visible • the spindle has formed and extends from the centrioles • chromosomes are visible as two sister chromatids held together at the centromere Prometaphase • also called late prophase or early metaphase • nuclear membrane disintegrates • the spindle attaches to centromere of each pair of sister chromatids Metaphase • the chromosomes line up completely along the equator of the cell Anaphase • the spindle fibers contract and pull the sister chromatids apart, toward opposite ends of the cell • karyokinesis – the process of the chromosomes being pulled apart Telophase • nuclear membrane begins to reform around the chromosomes • the chromosomes relax and unwind, take the form of chromatin • two cells form • cytokinesis – the process of the cell pinching inward and forming two cells Plant cell division • since the plant cell has a rigid cell wall it cannot pinch inward to form 2 new cells • the two daughter cells form inside • a cell plate forms from the Golgi or ER at the center of the cell which forms into a new cell wall