Concept 33 -...

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Concept 12.2 The mitotic phase alternates with interphase in the cell cycle. The  mitotic (M) phase  of the cell cycle, which includes mitosis and cytokinesis, alternates  with the much longer interphase . Interphase accounts for about 90% of the cell cycle. Interphase has three subphases: the  G phase  (“first gap”), the  S phase  (“synthesis”), and the  G phase  (“second gap”). The daughter cells may then repeat the cycle. During all three subphases, the cell grows by producing proteins and cytoplasmic organelles  such as mitochondria and endoplasmic reticulum. Chromosomes are duplicated only during the S phase, however. A typical human cell might divide once every 24 hours. Of this time, the M phase would last less than an hour and the S phase might take 10–12 hours,  or half the cycle. The rest of the time would be divided between the G and G phases. The G phase varies most in length from cell to cell. Mitosis is a continuum of changes. For convenience, mitosis is usually divided into five subphases:  prophase prometaphase metaphase anaphase , and  telophase . Cytokinesis completes the mitotic phase. In late interphase, the chromosomes have been duplicated but are not condensed. A nuclear membrane bounds the nucleus, which contains one or more nucleoli. The centrosome has replicated to form two centrosomes. In animal cells, each centrosome features two centrioles. In prophase, the chromosomes are tightly coiled, with sister chromatids joined together. The nucleoli disappear. The mitotic spindle begins to form. It is composed of centrosomes and the microtubules that  extend from them. The radial arrays of shorter microtubules that extend from the centrosomes are called asters.
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This note was uploaded on 01/04/2012 for the course BSC BSC1005 taught by Professor Orlando,rebecca during the Fall '10 term at Broward College.

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Concept 33 -...

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