10.2b Cell DivisionCell Division

2 Phases of the Cell Cycle  The cell cycle consists of  Interphase – normal cell activity  The mitotic phase – cell division  Cytokinesis - Cleavage

3 Interphase INTERPHASE Growth G 1 S (DNA synthesis) Growth G 2 Cell Divsion  G 1 - Cells undergo majority of growth  S - Each chromosome replicates (Synthesizes) to produce sister chromatids  Attached at centromere  Contains attachment site (kinetochore)  G 2 - Chromosomes condense - Assemble machinery for division such as centrioles

4 Directions for Mitosis Mix-Up 1. Discuss what is occurring in each image 2. Cut each of the images out and put them individually put them in order on your desk 3. Compare with your partner, if there are differences, discuss why 4. Once your both of you have the same order, come up and get a colored paper so that you can create a visual representation of Mitosis containing the following: 1. label the start of each step 2. Label what is occurring for each image 3. Label the following for at the start of each major step: nucleus, centrioles, spindle fibers, chromosomes, sister chromatids

5 Mitosis  Some haploid & diploid cells divide by mitosis.  Each new cell receives one copy of every chromosome that was present in the original cell.  Produces 2 new cells that are both genetically identical to the original cell. DNA duplication during interphase Mitosis Diploid Cell

6 Mitotic Division of an Animal Cell G 2 OF INTERPHASEPROPHASE Centrosomes (with centriole pairs) Chromatin (duplicated) Early mitotic spindle Centromere Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids

7 METAPHASEANAPHASETELOPHASE AND CYTOKINESIS Spindle Metaphase plate Nucleolus forming Cleavage furrow Nuclear envelope forming Centrosome at one spindle pole Daughter chromosomes Mitotic Division of an Animal Cell

8 Interphase A nuclear envelope bounds the nucleus. Two centrosomes have formed by replication of a single centrosome. Two centrioles Duplicated chromatin in the nucleus, duplicated during S phase INTERPHASE Centrosomes (with centriole pairs) Chromatin (duplicated) Nucleolus Nuclear envelope Plasma membrane

9 Prophase  Chromatin fibers condense and become duplicated chromosomes, sister chromatids, joined together by a centromere  The nuclear envelope breaks down  The mitotic spindle begins to form. It is composed of the centrosomes and the microtubules that extend from them.  The centrosomes move away from each other, propelled by the lengthening microtubules between them. PROPHASE Early mitotic spindle Centromere Chromosome, consisting of two sister chromatids

10 Metaphase Metaphase is the longest stage of mitosis, lasting about 20 minutes. The centrosomes are now at opposite ends of the cell. The chromosomes convene equidistant between the spindle’s two poles. The chromosomes’ centromeres lie on the metaphase plate. The entire apparatus of microtubules is called the spindle because of its shape. METAPHASE Spindle Metaphase plate Centrosome at one spindle pole

11 Anaphase two sister chromatids of each pair suddenly part. How many chromosomes part? 46 Each chromatid thus becomes a full- fledged chromosome. chromosomes begin moving toward opposite ends of the cell microtubules shorten Because these microtubules are attached at the centromere, the chromosomes move centromere first. The cell elongates as the microtubules lengthen. By the end of anaphase, the two ends of the cell have equivalent—and complete—collections of chromosomes. ANAPHASE Daughter chromosomes

12 Telophase Two daughter nuclei begin to form Nuclear envelopes begins to form The chromosomes become less condensed. Spindle begins to break apart Mitosis, the division of one nucleus into two genetically identical nuclei, is now complete. Telophase & Cytokinesis will occur at the same time TELOPHASE AND CYTOKINESIS Nucleolus forming Cleavage furrow Nuclear envelope forming

13 Mitosis in a plant cell Prophase. The chromatin is condensing. The nucleolus is beginning to disappear. Although not yet visible in the micrograph, the mitotic spindle is staring to from. Metaphase. The spindle is complete, and the chromosomes, attached to microtubules at their kinetochores, are all at the metaphase plate. Anaphase. The chromatids of each chromosome have separated, and the daughter chromosomes are moving to the ends of cell as their microtubles shorten. Telophase. Daughter nuclei are forming. Meanwhile, cytokinesis has started: The cell plate, which will divided the cytoplasm in two, is growing toward the perimeter of the parent cell Nucleus Nucleolus Chromatine condensing

14 Cytokinesis Chromosomes are condensed Cleavage of cell into two halves – Animal cells  Cell membrane is drawn inward until cytoplasm is pinched in two – Plant cells  Cell plate forms

15 Cytokinesis In Animal And Plant Cells Daughter cells Pinching cytoplasm Contractile cell membrane Daughter cells 100 µm 1 µm Vesicles forming cell plate Wall of patent cell Cell plate New cell wall (a) Cleavage of an animal cell (b) Cell plate formation in a plant cell

16 Interphase Cells have fully split Each daughter cell has identical set of duplicated chromosomes INTERPHASE Centrosomes (with centriole pairs) Chromatin (duplicated) Nucleolus Nuclear envelope Plasma membrane

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