AP Biology Lecture #20 Mitosis

Mitosis Prophase Prometaphase Metaphase Anaphase Telophase

The Mitotic Spindle The mitotic spindle is made of microtubules and proteins which help move the chromosomes around. It is made in the centrosome (an organelle) Asters are short microtubules that extend out from the centrosome Kinetochores are where the asters attach to chromosomes

Prophase Chromatin condenses visible chromosomes chromatids Centrioles move to opposite poles of cell animal cell Protein fibers cross cell to form mitotic spindle microtubules Nucleolus disappears Nuclear membrane breaks down

Prometaphase spindle fibers attach to centromeres creating kinetochores microtubules attach at kinetochores connect centromeres to centrioles chromosomes begin moving

Metaphase Centrosomes at opposite poles Centromeres are aligned Kinetochores of sister chromatids attached to microtubules (spindle)

Fig. 12-7 Aster Centrosome Sister chromatids Microtubules Chromosomes Metaphase plate Kineto- chores Centrosome 1 µm Overlapping nonkinetochore microtubules Kinetochore microtubules 0.5 µm

Anaphase Paired centromeres separate; sister chromatids liberated Chromosomes move to opposite poles Each pole now has a complete set of chromosomes

Separation of chromatids In anaphase, proteins holding together sister chromatids are inactivated separate to become individual chromosomes 1 chromosome 2 chromatids 2 chromosomes single-stranded double-stranded

Chromosome movement Kinetochores use motor proteins that “walk” chromosome along attached microtubule microtubule shortens by dismantling at kinetochore (chromosome) end Microtubules are NOT reeled in to centrioles like line on a fishing rod. The motor proteins walk along the microtubule like little hanging robots on a clothes line. In dividing animal cells, non-kinetochore microtubules are responsible for elongating the whole cell during anaphase, readying fro cytokinesis

Telophase Cytokinesis begins cell division Daughter nuclei form Nuclear envelopes arise Chromatin becomes less coiled Two new nuclei complete mitosis Cytokinesis begins cell division

Mitosis in whitefish blastula

Cytokinesis Animals Cytoplasmic division constriction belt of actin microfilaments around equator of cell cleavage furrow forms splits cell in two like tightening a draw string

Cytokinesis in Plants Plants cell plate forms vesicles line up at equator derived from Golgi vesicles fuse to form 2 cell membranes new cell wall laid down between membranes new cell wall fuses with existing cell wall

**In plant cells, cytokinesis begins when a new cell wall forms between the two new cells. **In animal cells, the two new cells pinch and pull apart

Mitosis in plant cell

onion root tip

Mitosis in Animals Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. has centrioles centrosome Animal Cell at Interphase aster 20 µm duplicated chromosome 20 µm spindle pole 9 µm metaphase plate chromosomes at 20µm daughter chromosome 20µm cleavage furrow 16µm nuclear envelope fragments centromere kinetochore nucleolus MITOSIS chromatin condenses nucleolus disappears spindle fibers forming spindle fiber kinetochore kinetochore spindle fiber polar spindle fiber Metaphase Centromeres of duplicated chromosomes of fully formed spindle). Kinetochore spindle are aligned at the metaphase plate (center fibers attached to the sister chromatids come from opposite spindle poles. Telophase Daughter cells are forming as nuclear envelopes and nucleoli reappear. Chromosomes will become indistinct chromatin. Early Prophase Centrosomes have duplicated. Chromatin is condensing into chromosomes, and the nuclear envelope is fragmenting. Prophase duplicated chromosomes are visible. Nucleolus has disappeared, and Centrosomes begin moving apart, and spindle is in process of forming. Prophase duplicated chromosomes are visible. Nucleolus has disappeared, and Centrosomes begin moving apart, and spindle is in process of forming. Anaphase chromosomes that move toward the spindle Sister chromatids part and become daughter poles. In this way, each pole receives the same number and kinds of chromosomes as the parent cell. centrosome lacks centrioles Plant Cell at Interphase 25µm cell wall chromosomes 6.2µm spindle pole lacks centrioles and aster 20µm spindle fibers 6.2µm 6.2µm cell plate 6.6µm Animal cell(Early prophase, Prophase, Metaphase, Anaphase, Telophase): © Ed Reschke; Animal cell(Prometaphase): © Michael Abbey/Photo Researchers, Inc.; Plant cell(Early prophase, Prometaphse): © Ed Reschke; Plant cell(Prophase, Metaphase, Anaphase): © R. Calentine/Visuals Unlimited; Plant cell(Telophase): © Jack M. Bostrack/Visuals Unlimited;

Bacterial Fission

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