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Mitosis and the Cell Cycle

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Why is mitotic cell division necessary?• 1. Asexual reproduction:

ex: bacteria (binary fission)

• 2. To replace damaged or dead cells

• 3. Growth and embryonic development of the organism

dividing bone marrow cells new blood cells

Sand dollar embryoAmoeba reproducing

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Binary Fission:

how some bacteria

reproduce

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frog embryo

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Phases of Mitosis

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•Interphase (NOT PART OF MITOSIS)

•Chromatin has already duplicated (DNA replication complete) but is not visible to naked eye

•Early prophase:

•Spindle microtubules are growing

•Chromatin condenses and is packed into discrete chromosomes

•Late prophase:

•Each chromosome consists of two identical chromatids formed by DNA replication in interphase and held together by a centromere

•Spindle microtubules extend from each pole to the equator

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Prometaphase:

• nuclear envelope disappears

• spindle microtubules attach to sister chromatids

Metaphase:• sister chromatids line up on the metaphase plate

• mitotic spindle forms

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Anaphase:• centromeres split, sister chromatids separate and each one is pulled to opposite ends of the cell

• cell begins to lengthen

• by the end of anaphase, there are 2 complete sets of genetic material at each pole

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Telophase:• nuclear envelope starts to reappear

• microtubule assembly starts to disintegrate

• chromatids begin to loosen

Cytokinesis:

•The cell divides to form 2 cells with genetically identical nuclei

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Animal Cell Division

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Plant Cell Division

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eukaryotic chromosomes (orange) in a kangaroo rat epithelial cell

16Differences in Cell Division Between Plant and Animal Cells

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Differences in Cell Division Between Plant and Animal Cells

• Plant Cells– There are no centrioles in plant cells– After anaphase, a new cell wall is formed across

the equator of the cell, with plasma membrane on both sides. This divides the cell into two cells

• Animal Cells– Centrioles are found at each pole of animal cells

during mitosis– After anaphase, the plasma membrane at the

equator is pulled inwards until it meets in the center of the cell, dividing it into two cells

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cell plate: dividing plant cell

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onion root tip: lots of dividing cells