Chapter 12 The Cell Cycle 2011 Pearson Education Inc Overview The Key Roles of Cell Division The ability of organisms to produce more of their own kind best distinguishes living things from nonliving matter The continuity of life is based on the reproduction of cells or cell division 2011 Pearson Education Inc In unicellular organisms division of one cell reproduces the entire organism Multicellular organisms depend on cell division for Development from a fertilized cell Growth Repair Cell division is an integral part of the cell cycle the life of a cell from formation to its own division 2011 Pearson Education Inc Concept 12 1 Most cell division results in genetically identical daughter cells Most cell division results in daughter cells with identical genetic information DNA The exception is meiosis a special type of division that can produce sperm and egg cells 2011 Pearson Education Inc Cellular Organization of the Genetic Material All the DNA in a cell constitutes the cell s genome A genome can consist of a single DNA molecule common in prokaryotic cells or a number of DNA molecules common in eukaryotic cells DNA molecules in a cell are packaged into chromosomes 2011 Pearson Education Inc Cellular Organization of the Genetic Material Genome Chromosomes Chromatin Somatic Cells Gametes Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Distribution of Chromosomes During Eukaryotic Cell Division In preparation for cell division DNA is replicated and the chromosomes condense Each duplicated chromosome has two sister chromatids joined copies of the original chromosome which separate during cell division The centromere is the narrow waist of the duplicated chromosome where the two chromatids are most closely attached 2011 Pearson Education Inc Figure 12 4 Sister chromatids Centromere 0 5 m During cell division the two sister chromatids of each duplicated chromosome separate and move into two nuclei Once separate the chromatids are called chromosomes 2011 Pearson Education Inc Figure 12 5 3 Chromosomes Chromosomal DNA molecules 1 2 3 Centromere Chromosome arm Chromosome duplication including DNA replication and condensation Sister chromatids Separation of sister chromatids into two chromosomes Eukaryotic cell division consists of Mitosis the division of the genetic material in the nucleus Cytokinesis the division of the cytoplasm Gametes are produced by a variation of cell division called meiosis Meiosis yields nonidentical daughter cells that have only one set of chromosomes half as many as the parent cell 2011 Pearson Education Inc Concept 12 2 The mitotic phase alternates with interphase in the cell cycle In 1882 the German anatomist Walther Flemming developed dyes to observe chromosomes during mitosis and cytokinesis 2011 Pearson Education Inc Phases of the Cell Cycle The cell cycle consists of Mitotic M phase Interphase 2011 Pearson Education Inc Interphase about 90 of the cell cycle can be divided into subphases G1 phase first gap S phase synthesis G2 phase second gap 2011 Pearson Education Inc Figure 12 6 INTERPHASE G1 S DNA synthesis sis e ki n Mitosis y t o C MITOTIC M PHASE G2 Mitosis is conventionally divided into five phases Prophase Prometaphase Metaphase Anaphase Telophase Cytokinesis overlaps the latter stages of mitosis 2011 Pearson Education Inc BioFlix Mitosis Figure 12 7 G2 of Interphase Prophase Prometaphase Metaphase Anaphase Telophase and Cytokinesis Centrosomes with centriole pairs Chromatin duplicated Early mitotic spindle Aster Centromere Fragments of nuclear envelope Nonkinetochore microtubules Metaphase plate Cleavage furrow Nucleolus forming m 0 1 Nucleolus Nuclear envelope Plasma membrane Chromosome consisting of two sister chromatids Kinetochore Kinetochore microtubule Spindle Centrosome at one spindle pole Daughter chromosomes Nuclear envelope forming Figure 12 8 Sister chromatids Aster Centrosome Metaphase plate imaginary Microtubules Chromosomes Centrosome 1 m Overlapping nonkinetochore microtubules Kinetochore microtubules Kineto chores 0 5 m Cytokinesis A Closer Look In animal cells cytokinesis occurs by a process known as cleavage forming a cleavage furrow In plant cells a cell plate forms during cytokinesis 2011 Pearson Education Inc Animation Cytokinesis Figure 12 10 a Cleavage of an animal cell SEM b Cell plate formation in a plant cell TEM Cleavage furrow 100 m Vesicles forming cell plate Wall of parent cell 1 m Cell plate New cell wall Contractile ring of microfilaments Daughter cells Daughter cells Binary Fission in Bacteria Prokaryotes bacteria and archaea reproduce by a type of cell division called binary fission In binary fission the chromosome replicates beginning at the origin of replication and the two daughter chromosomes actively move apart The plasma membrane pinches inward dividing the cell into two 2011 Pearson Education Inc Figure 12 12 4 Origin of replication Cell wall Plasma membrane E coli cell Bacterial chromosome 1 Chromosome replication begins Two copies of origin Origin Origin 2 Replication continues 3 Replication finishes 4 Two daughter cells result Concept 12 3 The eukaryotic cell cycle is regulated by a molecular control system The frequency of cell division varies with the type These differences result from regulation at the Cancer cells manage to escape the usual controls of cell molecular level on the cell cycle 2011 Pearson Education Inc The Cell Cycle Control System The sequential events of the cell cycle are directed by a distinct cell cycle control system which is similar to a clock The cell cycle control system is regulated by both internal and external controls The clock has specific checkpoints where the cell cycle stops until a go ahead signal is received 2011 Pearson Education Inc Loss of Cell Cycle Controls in Cancer Cells Cancer cells do not respond normally to the body s control mechanisms Cancer cells may not need growth factors to grow and divide They may make their own growth factor They may convey a growth factor s signal without the presence of the growth factor They may have an abnormal cell cycle control system 2011 Pearson Education Inc A normal cell is converted to a cancerous cell by a process called transformation Cancer cells that are not eliminated by the immune system form tumors masses of abnormal cells within otherwise normal tissue If abnormal cells remain at the original site the lump is called a benign tumor Malignant tumors invade surrounding tissues and can