CELL DIVISION AND REPRODUCTION Mitosis 8.1-8.20 © 2012 Pearson Education, Inc. 1

8.1 Cell division plays many important roles in the lives of organisms Cell division is reproduction at the cellular level, requires the duplication of chromosomes, and sorts new sets of chromosomes into the resulting pair of daughter cells. © 2012 Pearson Education, Inc. 2

8.1 Cell division plays many important roles in the lives of organisms Two types of cell division Mitosis asexual reproduction reproduction of single-celled organisms, reproduction of multicellular organisms growth: increase in size onion root tips fertilized eggadult repair and replacement of cells Student Misconceptions and Concerns 1. As the authors note in Module 8.1, biologists use the term daughter to indicate offspring and not gender. Students with little experience in this terminology can easily become confused. 2. Some basic familiarity or faint memory of mitosis and meiosis might result in a lack of enthusiasm for mitosis and meiosis in some of your students. Consider beginning such lectures with important topics related to cellular reproduction. For example, cancer cells reproduce uncontrollably, stem cells have the capacity to regenerate lost or damaged tissues, and the study of embryonic stem cells is variously restricted and regulated. Teaching Tips Sometimes the most basic questions can challenge students and get them focused on the subject at hand. Consider asking your students why we expect that dogs will produce dogs, cats will produce more cats, and chickens will only produce chickens. Why does like produce like? 3

8.1 Cell division plays many important roles in the lives of organisms Two types of cell division Meiosis Production of gametes (reproductive cells) Used in sexual reproduction © 2012 Pearson Education, Inc.

8.2 Prokaryotes reproduce by binary fission (Sexual or asexual reproduction?) Prokaryotes (bacteria and archaea) reproduce by binary fission (“dividing in half”). © 2012 Pearson Education, Inc. 5

Division into two daughter cells Figure 8.2A_s3 Plasma membrane Prokaryotic chromosome Cell wall Duplication of the chromosome and separation of the copies 1 Continued elongation of the cell and movement of the copies 2 Division into two daughter cells 3 6

THE EUKARYOTIC CELL CYCLE AND MITOSIS © 2012 Pearson Education, Inc. 7

8.3 Eukaryotic chromosomes Eukaryotic cells store most of their genes on multiple chromosomes within the nucleus. (How many chromosomes in a human cell?) © 2012 Pearson Education, Inc. 8

8.3 Chromatin and chromosomes Eukaryotic chromosomes are composed of chromatin DNA + protein To prepare for division, the chromatin becomes chromosomes Why is this coiling of chromatin important? © 2012 Pearson Education, Inc. 9

Chromosomes DNA molecules Sister chromatids Chromosome duplication Figure 8.3B Chromosomes DNA molecules Sister chromatids Chromosome duplication Sister chromatids Centromere Figure 8.3B Chromosome duplication and distribution Chromosome distribution to the daughter cells 10

8.4 The cell cycle multiplies cells The cell cycle is an ordered sequence of events that extends from the time a cell is first formed from a dividing parent cell until its own division.? Do all cells divide © 2012 Pearson Education, Inc. 11

I N T E R P H A S G1 (first gap) S (DNA synthesis) M G2 (second gap) Figure 8.4 I N T E R P H A S G1 (first gap) S (DNA synthesis) M Cytokinesis G2 (second gap) Mitosis Figure 8.4 The eukaryotic cell cycle T MI O IC PH A SE 12

8.4 Interphase Most of the cell cycle is spent in Interphase (90%) Cell performs its various functions. white blood cells Intestinal cells Pancreatic cells A cell will Make more cytoplasm/create organelles/grow in size Synthesize proteins Synthesize DNA

8.5 Cell division (10 %) Mitosis: Chromosomes are divided equally between two identical daughter nuclei prophase, prometaphase metaphase, anaphase, and telophase. Cytokinesis: cytoplasm is divided Two identical daughter cells are produced.. © 2012 Pearson Education, Inc. 14

8.5 Cell division is a continuum of dynamic changes A mitotic spindle is required to divide the chromosomes, composed of microtubules, and produced by centrosomes organize microtubule arrangement and contain a pair of centrioles in animal cells. Video: Animal Mitosis Video: Sea Urchin (time lapse) © 2012 Pearson Education, Inc. 15

(with centriole pairs) Fragments of the nuclear envelope Early mitotic Figure 8.5_1 MITOSIS INTERPHASE Prophase Prometaphase Centrosomes (with centriole pairs) Fragments of the nuclear envelope Early mitotic spindle Centrosome Kinetochore Centrioles Chromatin Centromere Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Spindle microtubules 16

Telophase and Cytokinesis Figure 8.5_5 MITOSIS Metaphase Anaphase Telophase and Cytokinesis Metaphase plate Cleavage furrow Nuclear envelope forming Mitotic spindle Daughter chromosomes 17

8.5 Interphase The cytoplasmic contents double, Two centrosomes form, The cytoplasmic contents double, Two centrosomes form, chromosomes duplicate in the nucleus during the S phase, and Nucleoli, sites of ribosome assembly, are visible. © 2012 Pearson Education, Inc. 18

8.5 Cell division: Mitosis 8.5 Cell division: Mitosis Prophase In the cytoplasm microtubules begin to emerge from centrosomes, forming the spindle. In the nucleus chromosomes coil and become compact and nucleoli disappear. © 2012 Pearson Education, Inc. 19

8.5 Cell division: Mitosis 8.5 Cell division: Mitosis Prometaphase Spindle microtubules reach chromosomes, where they attach at kinetochores on the centromeres of sister chromatids and move chromosomes to the center of the cell through associated protein “motors.” The nuclear envelope disappears. © 2012 Pearson Education, Inc. 20

8.5 Cell division: Mitosis 8.5 Cell division: Mitosis Metaphase The mitotic spindle is fully formed. Chromosomes align at the cell equator. Kinetochores of sister chromatids are facing the opposite poles of the spindle. © 2012 Pearson Education, Inc. 21

8.5 Cell division: Mitosis 8.5 Cell division: Mitosis Anaphase Sister chromatids separate Daughter chromosomes are moved to opposite poles motor proteins move the chromosomes along the spindle microtubules and kinetochore microtubules shorten. The cell elongates © 2012 Pearson Education, Inc. 22

8.5 Cell division: Mitosis 8.5 Cell division: Mitosis Telophase The cell continues to elongate. The nuclear envelope forms around chromosomes at each pole Chromatin uncoils and nucleoli reappear. The spindle disappears. © 2012 Pearson Education, Inc. 23

8.5 Cell division: Mitosis During cytokinesis, the cytoplasm is divided into separate cells. © 2012 Pearson Education, Inc. 24

8.6 Cytokinesis differs for plant and animal cells In animal cells, cytokinesis occurs as a cleavage furrow forms from a contracting ring of microfilaments, interacting with myosin © 2012 Pearson Education, Inc. 25

Cleavage furrow Daughter cells Figure 8.6A Cytokinesis Cleavage furrow Contracting ring of microfilaments Daughter cells Figure 8.6A Cleavage of an animal cell Cleavage furrow 26

8.6 Cytokinesis differs for plant and animal cells In plant cells, cytokinesis occurs as a cell plate forms in the middle, from vesicles containing cell wall material, Animation: Cytokinesis © 2012 Pearson Education, Inc. 27

Cytokinesis New cell wall Cell wall of the parent cell Cell wall Figure 8.6B Cytokinesis New cell wall Cell wall of the parent cell Cell wall Plasma membrane Daughter nucleus Vesicles containing cell wall material Cell plate Daughter cells Figure 8.6B Cell plate formation in a plant cell Cell plate forming 28