The Cell Cycle and Cellular Reproduction Chapter 9 Outline Interphase Mitotic Stage Cell Cycle Control Apoptosis Mitosis Mitosis in Animal Cells Cytokinesis Cancer Prokaryotic Cell Division 1 2 Interphase Most of the cell cycle is spent in interphase. G 1 - Cell doubles its organelles and accumulates materials needed for DNA synthesis. S - DNA replication. G 2 - Cell synthesizes proteins necessary for cell division. Mitotic Stage Cell division stage that includes mitosis (nuclear division) and cytokinesis (cytoplasm division). 3 4
Cell Cycle Cell Cycle Control Researchers have identified internal signal protein (cyclin) that increases and decreases as cell cycle continues. Must be present for the cell to proceed from the G 2 stage to the M stage and from G 1 stage to S stage.! Allows time for any damage to be repaired. 5 6 Cell Cycle Control Apoptosis Often defined as programmed cell death. Cells routinely harbor enzymes (caspases) necessary for apoptosis to occur.! Ordinarily held in check by inhibitors, but can be unleashed by internal or external signals. Mitosis increases and apoptosis decreases the number of somatic cells. 7 8
Fig. 9A Apoptosis 9 10 Mitosis When a eukaryotic cell is not undergoing division, the DNA within the nucleus is a tangled mass of chromatin. Condenses into chromosomes! Each species has a characteristic number of chromosomes. " Diploid (2n) - Two of each kind. " Haploid (1n) - One of each kind. Mitosis During mitosis, a diploid nucleus divides to produce diploid daughter nuclei. Two identical chromatids are called sister chromatids.! Attached to each other at centromere. " During nuclear division, sister chromatids separate at the centromeres, and each duplicated chromosome gives rise to two daughter chromosomes. 11 12
Duplicated Chromosomes Mitosis in Animal Cells Each centromere in an animal cell contains a pair of barrel-shaped organelles (centrioles) and an array of short microtubules (aster). Centromeres organize mitotic spindle, which contains many fibers, each composed of a microtubule bundle. 13 14 Prophase Mitosis in Animal Cells Chromatin has condensed. Nucleolus disappears. Nuclear envelope disintegrates. Spindle begins to assemble. Prometaphase Kinetochores develop on centromere.! Attach sister chromatids to spindle fibers. 15 16
Fig. 9.4p154d Fig. 9.4p154e 17 18 Fig. 9.4p154f Metaphase Mitosis in Animal Cells Chromosomes, attached to kinetochore fibers, are in alignment at center of cell. Anaphase Sister chromatids split, producing daughter chromosomes.! Daughter chromosomes are pulled to opposite poles. 19 20
Telophase Mitosis in Animal Cells Spindle disappears as new nuclear envelopes form around the daughter chromosomes.! Chromosomes become diffuse chromatin again.! Nucleolus appears in each daughter nucleus. 21 22 Fig. 9.4p155d Fig. 9.4p155e 23 24
Fig. 9.4p155f Plant Cell Division Meristematic plant tissue retains the ability to divide throughout the plant s life. Found at root and shoot tips. 25 26 Phases of Mitosis in Plant Cells Cytokinesis Cytokinesis accompanies mitosis in most cells, but not all. Mitosis without cytokinesis results in a multinucleated cell.! Begins in anaphase, continues in telophase, but does not reach completion until the following interphase begins. 27 28
Cytokinesis Cytokinesis in Animal Cells Animal Cells Cleavage furrow, membrane indentation between daughter nuclei, begins as anaphase nears completion.! Deepens when a band of actin filaments (contractile ring) forms a circular constriction between the two daughter cells. 29 30 Cytokinesis Cytokinesis in Plant Cells Plant Cells Rigid cell wall surrounding plant cells does not permit cytokinesis by furrowing.! Begins with formation of a cell plate which eventually becomes new plasma membrane between the daughter cells. 31 32
Prokaryotic Cell Division Binary Fission Asexual Reproduction - offspring are genetically identical to the parent. Binary fission produces two (binary) daughter cells that are identical to the original parent.! Prokaryotes contain a single chromosome with only a few proteins. 33 34 Review Interphase Mitotic Stage Cell Cycle Control Apoptosis Mitosis Mitosis in Animal Cells Cytokinesis Cancer Prokaryotic Cell Division 35 36