8.6 Cell division is a continuum of dynamic changes Mitosis is divided into five phases: Prophase Prometaphase Metaphase Anaphase Telophase/Cytokinesis Cytokinesis is well underway by late telophase For the Cell Biology Video Myosin and Cytokinesis, go to Animation and Video Files.

INTERPHASE PROPHASE PROMETAPHASE INTERPHASE PROPHASE PROMETAPHASE Centrosomes (with centriole pairs) Chromatin Early mitotic spindle Centrosome Fragments of nuclear envelope Kinetochore Figure 8.6 The stages of cell division. Centromere Nuclear envelope Plasma membrane Spindle microtubules Chromosome, consisting of two sister chromatids Nucleolus

Figure 8.6 The stages of cell division. INTERPHASE

8.6 Cell division is a continuum of dynamic changes Interphase In the cytoplasm Cytoplasmic contents double Two centrosomes form Animal cells have centrioles within the centrosomes, plants do not In the nucleus Chromosomes duplicate during the S phase 2 Nucleoli are visible Teaching Tips

Figure 8.6 The stages of cell division. PROPHASE

8.6 Cell division is a continuum of dynamic changes Prophase In the cytoplasm Microtubules begin to emerge from centrosomes, forming the spindle In the nucleus Chromosomes coil and become compact Nucleoli disappear

Figure 8.6 The stages of cell division. PROMETAPHASE

8.6 Cell division is a continuum of dynamic changes Prometaphase Spindle microtubules reach chromosomes, where they Attach at kinetochores on the centromeres of sister chromatids Move chromosomes to the center of the cell through associated protein “motors” Other microtubules meet those from the opposite poles The nuclear envelope disappears Teaching Tips 1. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT: the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase are represented in this acronym. 2. The authors note that animals, but not plants, have a pair of centrioles in their centrosomes. They add that the role of centrioles in cell division is a mystery. Students might not appreciate all that remains to be explained in biology. Sharing the existence of such mysteries with them promotes critical thinking skills and helps them imagine a place for themselves in future research.

TELOPHASE AND CYTOKINESIS METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Nucleolus forming Metaphase plate Cleavage furrow Figure 8.6 The stages of cell division. Nuclear envelope forming Daughter chromosomes Spindle

Figure 8.6 The stages of cell division. METAPHASE

Cell division is a continuum of dynamic changes Metaphase Spindle is fully formed Chromosomes align at the cell equator Kinetochores of sister chromatids are facing the opposite poles of the spindle

Figure 8.6 The stages of cell division. ANAPHASE

8.6 Cell division is a continuum of dynamic changes Anaphase Sister chromatids separate at the centromeres Daughter chromosomes are moved to opposite poles of the cell when kinetochore microtubules shorten The cell elongates due to lengthening of nonkinetochore microtubules Applying Your Knowledge By the end of anaphase, How many chromosomes are present in one cell? 92 (Once the sister chromatids separate, they are considered to be individual chromosomes.) How many chromatids are present in one cell? 0 Teaching Tips 1. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT: the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase are represented in this acronym. 2. The authors note that animals, but not plants, have a pair of centrioles in their centrosomes. They add that the role of centrioles in cell division is a mystery. Students might not appreciate all that remains to be explained in biology. Sharing the existence of such mysteries with them promotes critical thinking skills and helps them imagine a place for themselves in future research. C.

TELOPHASE AND CYTOKINESIS Figure 8.6 The stages of cell division. TELOPHASE AND CYTOKINESIS

8.6 Cell division is a continuum of dynamic changes Telophase The cell continues to elongate The nuclear envelope forms around chromosomes at each pole, establishing daughter nuclei Chromatin uncoils Nucleoli reappear The spindle disappears C

8.6 Cell division is a continuum of dynamic changes Cytokinesis Cytoplasm is divided into separate cells Applying Your Knowledge By the end of cytokinesis How many chromosomes are present in one human cell? How many chromatids are present in one human cell? C