Biology Chapter 12: Mitosis PDF

Chapter 07 Chapter 12 Cell Structure and Function Mitosis Lecture Presentations by Ni...

Chapter 07 Chapter 12 Cell Structure and Function Mitosis Lecture Presentations by Nicole Tunbridge and © 2021 Pearson Education Ltd. Kathleen Fitzpatrick © 2018 Pearson Education Ltd. 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 © 2018 Pearson Education Ltd. Figure 12.1 © 2018 Pearson Education Ltd. Figure 12.1a Chromosomes (blue) are attached by specific proteins (green) to cell machinery (red) and are moved during division of a rat kangaroo cell. © 2018 Pearson Education Ltd.  In unicellular organisms, division of one cell reproduces the entire organism  Multicellular eukaryotes depend on cell division for  development from a fertilized egg  growth  repair  Cell division is an integral part of the cell cycle, the life of a cell from formation to its own division © 2018 Pearson Education Ltd. Figure 12.2 100 µm (a) Asexual reproduction 50 µm (b) Growth and development (c) Tissue renewal 20 µm © 2018 Pearson Education Ltd. Concept 12.1: Most cell division results in genetically identical daughter cells  Most cell division results in two daughter cells with identical genetic information, DNA  The exception is meiosis, a special type of division that can produce sperm and egg cells © 2018 Pearson Education Ltd. 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 © 2018 Pearson Education Ltd. Figure 12.3 20 µm © 2018 Pearson Education Ltd.  Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein that condenses during cell division  Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus  Somatic cells (nonreproductive cells) have two sets of chromosomes  Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells © 2018 Pearson Education Ltd. 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), attached along their lengths by cohesins  The centromere is the narrow “waist” of the duplicated chromosome, where the two chromatids are most closely attached © 2018 Pearson Education Ltd. Figure 12.4 Sister chromatids Centromeres, one on each sister chromatid 0.5 µm © 2018 Pearson Education Ltd.  During cell division, the two sister chromatids of each duplicated chromosome separate and move into two nuclei  Once separate, the chromatids are called chromosomes © 2018 Pearson Education Ltd. Figure 12.5_1 1 Chromosomes Chromosomal DNA molecules Centromere Chromosome arm © 2018 Pearson Education Ltd. Figure 12.5_2 1 Chromosomes Chromosomal DNA molecules Centromere Chromosome arm Chromosome duplication 2 Sister chromatids © 2018 Pearson Education Ltd. Figure 12.5_3 1 Chromosomes Chromosomal DNA molecules Centromere Chromosome arm Chromosome duplication 2 Sister chromatids Separation of sister chromatids 3 © 2018 Pearson Education Ltd.  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 half as many chromosomes as the parent cell © 2018 Pearson Education Ltd. 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 © 2018 Pearson Education Ltd. Phases of the Cell Cycle  The cell cycle consists of  mitotic (M) phase (mitosis and cytokinesis)  interphase (cell growth and copying of chromosomes in preparation for cell division) © 2018 Pearson Education Ltd.  Interphase (about 90% of the cell cycle) can be divided into three phases:  G1 phase (“first gap”)  S phase (“synthesis”)  G2 phase (“second gap”)  The cell grows during all three phases, but chromosomes are duplicated only during the S phase © 2018 Pearson Education Ltd. Figure 12.6 G1 S (DNA synthesis) sis e k in G2 is o yt s ito C M © 2018 Pearson Education Ltd.  Mitosis is conventionally broken down into five stages:  prophase  prometaphase  metaphase  anaphase  telophase © 2018 Pearson Education Ltd. Figure 12.7a 10 µm G2 of Interphase Prophase Prometaphase Centrosomes Chromosomes Early mitotic Fragments Nonkinetochore (with centriole (duplicated, Aster of nuclear spindle microtubules pairs) uncondensed) Centromere envelope Plasma Nucleolus Two sister chromatids Kinetochore Kinetochore Nuclear membrane of one chromosome microtubules envelope © 2018 Pearson Education Ltd. Figure 12.7b 10 µm Metaphase Anaphase Telophase and Cytokinesis Metaphase Cleavage Nucleolus plate furrow forming Daughter chromosomes Spindle Nuclear Centrosome at envelope one spindle pole forming © 2018 Pearson Education Ltd. Figure 12.7c G2 of Interphase Prophase Centrosomes Chromosomes Early mitotic (with centriole (duplicated, Aster spindle pairs) uncondensed) Centromere Plasma Nucleolus Two sister chromatids Nuclear membrane of one chromosome envelope © 2018 Pearson Education Ltd. Figure 12.7d Prometaphase Metaphase Fragments Nonkinetochore Metaphase of nuclear microtubules plate envelope Kinetochore Kinetochore Spindle Centrosome at microtubules one spindle pole © 2018 Pearson Education Ltd. Figure 12.7e Anaphase Telophase and Cytokinesis Cleavage Nucleolus furrow forming Daughter chromosomes Nuclear envelope forming © 2018 Pearson Education Ltd. The Mitotic Spindle: A Closer Look  The mitotic spindle is a structure made of microtubules that controls chromosome movement during mitosis  In animal cells, assembly of spindle microtubules begins in the centrosome, the microtubule- organizing center  The centrosome replicates during interphase, forming two centrosomes that migrate to opposite ends of the cell during prophase and prometaphase © 2018 Pearson Education Ltd.  An aster (a radial array of short microtubules) extends from each centrosome  The spindle includes the centrosomes, the spindle microtubules, and the asters © 2018 Pearson Education Ltd.  During prometaphase, some spindle microtubules attach to the kinetochores of chromosomes and begin to move the chromosomes  Kinetochores are protein complexes associated with centromeres  At metaphase, the chromosomes are all lined up at the metaphase plate, a plane midway between the spindle’s two poles © 2018 Pearson Education Ltd. Figure 12.8 Aster Centrosome Sister chromatids Metaphase plate (imaginary) Kineto- chores Microtubules Overlapping nonkinetochore microtubules Kinetochore microtubules Chromosomes Centrosome 1 µm 0.5 µm © 2018 Pearson Education Ltd. Figure 12.8a Microtubules Chromosomes Centrosome 1 µm © 2018 Pearson Education Ltd. Figure 12.8b Kinetochores Kinetochore microtubules 0.5 µm © 2018 Pearson Education Ltd.  In anaphase the cohesins are cleaved by an enzyme called separase  Sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell  The microtubules shorten by depolymerizing at their kinetochore ends © 2018 Pearson Education Ltd.  Results of a clever experiment suggest that motor proteins on kinetochores “walk” the chromosomes along the microtubules during anaphase  The depolymerization of the microtubules at the kinetochore ends occurs after the motor proteins have passed  This is called the “Pac-man” mechanism © 2018 Pearson Education Ltd. Figure 12.9 Experiment Results Kinetochore Spindle pole Conclusion Chromosome Mark movement Kinetochore Motor Microtubule protein Tubulin Chromosome subunits Data from G. J. Gorbsky, P. J. Sammak, and G. G. Borisy, Chromosomes move poleward in anaphase along stationary microtubules that coordinately disassemble from their kinetochore ends, Journal of Cell Biology 104:9–18 (1987). Figure 12.9a Experiment Kinetochore Spindle pole Mark Data from G. J. Gorbsky, P. J. Sammak, and G. G. Borisy, Chromosomes move poleward in anaphase along stationary microtubules that coordinately disassemble from their kinetochore ends, Journal of Cell Biology 104:9–18 (1987). Figure 12.9b Results Conclusion Chromosome movement Kinetochore Motor Tubulin Microtubule protein subunits Chromosome Data from G. J. Gorbsky, P. J. Sammak, and G. G. Borisy, Chromosomes move poleward in anaphase along stationary microtubules that coordinately disassemble from their kinetochore ends, Journal of Cell Biology 104:9–18 (1987).  Nonkinetochore microtubules from opposite poles overlap and push against each other, elongating the cell  At the end of anaphase, duplicate groups of chromosomes have arrived at opposite ends of the elongated cell  Cytokinesis begins during anaphase or telophase, and the spindle eventually disassembles © 2018 Pearson Education Ltd. 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 © 2018 Pearson Education Ltd. Figure 12.10 (a) Cleavage of an animal cell (SEM) (b) Cell plate formation in a plant cell (TEM) Cleavage furrow 100 µm Vesicles Wall of parent cell 1 µm forming New cell cell plate Cell plate wall Contractile ring of Daughter cells microfilaments Daughter cells © 2018 Pearson Education Ltd. Figure 12.10a Cleavage furrow 100 µm © 2018 Pearson Education Ltd. Figure 12.10b Vesicles Wall of parent cell 1 µm forming cell plate © 2018 Pearson Education Ltd. Figure 12.11 Nucleus Chromosomes Nucleolus condensing Chromosomes 10 µm 1 Prophase 2 Prometaphase Cell plate 3 Metaphase 4 Anaphase 5 Telophase © 2018 Pearson Education Ltd. Figure 12.11a Nucleus Chromosomes Nucleolus condensing 1 Prophase 10 µm © 2018 Pearson Education Ltd. Figure 12.11b Chromosomes 2 Prometaphase 10 µm © 2018 Pearson Education Ltd. Figure 12.11c 3 Metaphase 10 µm © 2018 Pearson Education Ltd. Figure 12.11d 4 Anaphase 10 µm © 2018 Pearson Education Ltd. Figure 12.11e Cell plate 5 Telophase 10 µm © 2018 Pearson Education Ltd. 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 © 2018 Pearson Education Ltd. Figure 12.12_1 Origin of Cell wall replication Plasma membrane Bacterial cell Bacterial 1 Chromosome replication Two copies chromosome begins. of origin © 2018 Pearson Education Ltd. Figure 12.12_2 Origin of Cell wall replication Plasma membrane Bacterial cell Bacterial 1 Chromosome replication Two copies chromosome begins. of origin Origin Origin 2 One copy of the origin is now at each end of the cell. © 2018 Pearson Education Ltd. Figure 12.12_3 Origin of Cell wall replication Plasma membrane Bacterial cell Bacterial 1 Chromosome replication Two copies chromosome begins. of origin Origin Origin 2 One copy of the origin is now at each end of the cell. 3 Replication finishes. © 2018 Pearson Education Ltd. Figure 12.12_4 Origin of Cell wall replication Plasma membrane Bacterial cell Bacterial 1 Chromosome replication Two copies chromosome begins. of origin Origin Origin 2 One copy of the origin is now at each end of the cell. 3 Replication finishes. 4 Two daughter cells result. © 2018 Pearson Education Ltd. The Evolution of Mitosis  Because prokaryotes evolved before eukaryotes, mitosis probably evolved from binary fission  Certain protists exhibit types of cell division that seem intermediate between binary fission and mitosis © 2018 Pearson Education Ltd. Figure 12.13 Bacterial Kinetochore chromosome microtubule Intact nuclear envelope (a) Bacteria (c) Diatoms and some yeasts Chromosomes Kinetochore Microtubules microtubule Intact nuclear Fragments of envelope nuclear envelope (b) Dinoflagellates (d) Most eukaryotes © 2018 Pearson Education Ltd. Concept 12.3: The eukaryotic cell cycle is regulated by a molecular control system  The frequency of cell division varies with the type of cell  These differences result from regulation at the molecular level  Cancer cells manage to escape the usual controls on the cell cycle © 2018 Pearson Education Ltd. The Cell Cycle Control System  The cell cycle appears to be driven by specific chemical signals present in the cytoplasm  Some evidence for this hypothesis comes from experiments in which cultured mammalian cells at different phases of the cell cycle were fused to form a single cell with two nuclei © 2018 Pearson Education Ltd. Figure 12.14 Experiment Experiment 1 Experiment 2 S G1 M G1 Results S S M M G1 nucleus G1 nucleus began immediately entered mitosis without S phase and DNA chromosome was synthesized. duplication. Conclusion Molecules present in the cytoplasm control the progression to S and M phases. Data from R. T. Johnson and P. N. Rao, Mammalian cell fusion: Induction of premature chromosome condensation in interphase nuclei, Nature 226:717–722 (1970). © 2018 Pearson Education Ltd.  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 © 2018 Pearson Education Ltd. Figure 12.15 G1 checkpoint Control G1 system S M G2 M checkpoint G2 checkpoint © 2018 Pearson Education Ltd. The Cell Cycle Clock: Cyclins and Cyclin- Dependent Kinases  Two types of regulatory proteins are involved in cell cycle control: cyclins and cyclin-dependent kinases (Cdks)  The activity of a Cdk rises and falls with changes in concentration of its cyclin partner  MPF (maturation-promoting factor) is a cyclin-Cdk complex that triggers a cell’s passage past the G2 checkpoint into the M phase © 2018 Pearson Education Ltd. Figure 12.16a M G1 S G2 M G1 S G2 M G1 MPF activity Cyclin concentration Time (a) Fluctuation of MPF activity and cyclin concentration during the cell cycle © 2018 Pearson Education Ltd. Figure 12.16b 1 S G Cdk M Degraded G2 cyclin G2 Cdk Cyclin is checkpoint degraded Cyclin MPF (b) Molecular mechanisms that help regulate the cell cycle © 2018 Pearson Education Ltd. Stop and Go Signs: Internal and External Signals at the Checkpoints  Many signals registered at checkpoints come from cellular surveillance mechanisms within the cell  Checkpoints also register signals from outside the cell  Three important checkpoints are those in the G1, G2, and M phases © 2018 Pearson Education Ltd.  For many cells, the G1 checkpoint seems to be the most important  If a cell receives a go-ahead signal at the G1 checkpoint, it will usually complete the S, G2, and M phases and divide  If the cell does not receive the go-ahead signal, it will exit the cycle, switching into a nondividing state called the G0 phase © 2018 Pearson Education Ltd. Figure 12.17 G1 checkpoint G0 G1 G1 Without go-ahead signal, cell With go-ahead signal, cell G1 enters G0. continues cell cycle. S (a) G1 checkpoint M G2 G1 G1 M G2 M G2 M checkpoint G2 Anaphase checkpoint Prometaphase Metaphase Without full chromosome attachment, With full chromosome stop signal is received. attachment, go-ahead signal is received. (b) M checkpoint © 2018 Pearson Education Ltd. Figure 12.17a G1 checkpoint G0 G1 G1 Without go-ahead signal, cell With go-ahead signal, cell continues enters G0. cell cycle. (a) G1 checkpoint © 2018 Pearson Education Ltd. Figure 12.17b G1 G1 M G2 M G2 M checkpoint G2 Anaphase checkpoint Prometaphase Metaphase Without full chromosome attachment, With full chromosome attachment, stop signal is received. go-ahead signal is received. (b) M checkpoint © 2018 Pearson Education Ltd.  An example of an internal signal is that cells will not begin anaphase until all chromosomes are properly attached to the spindle at the metaphase plate  This mechanism ensures that daughter cells have the correct number of chromosomes © 2018 Pearson Education Ltd.  External factors that influence cell division include specific growth factors  Growth factors are released by certain cells and stimulate other cells to divide  Platelet-derived growth factor (PDGF) is made by blood cell fragments called platelets  In density-dependent inhibition, crowded cells will stop dividing © 2018 Pearson Education Ltd. Figure 12.18_1 Scalpels 1 A sample of human connective tissue is cut up into small pieces. Petri dish © 2018 Pearson Education Ltd. Figure 12.18_2 Scalpels 1 A sample of human connective tissue is cut up into small pieces. Petri dish 2 Enzymes digest the extracellular matrix, resulting in a suspension of free fibroblasts. © 2018 Pearson Education Ltd. Figure 12.18_3 Scalpels 1 A sample of human connective tissue is cut up into small pieces. Petri dish 2 Enzymes digest the extracellular matrix, resulting in a suspension of free fibroblasts. 3 Cells are transferred to culture vessels. © 2018 Pearson Education Ltd. Figure 12.18_4 Scalpels 1 A sample of human connective tissue is cut up into small pieces. Petri dish 2 Enzymes digest the extracellular matrix, resulting in a suspension of free fibroblasts. 3 Cells are transferred to culture vessels. 4 PDGF is added to half the vessels. 10 µm Without PDGF With PDGF Cultured fibroblasts (SEM) © 2018 Pearson Education Ltd.  Most cells also exhibit anchorage dependence—to divide, they must be attached to a substratum  Density-dependent inhibition and anchorage dependence check the growth of cells at an optimal density  Cancer cells exhibit neither type of regulation of their division © 2018 Pearson Education Ltd. Figure 12.19 Anchorage dependence: cells require a surface for division Density-dependent inhibition: cells form a single layer Density-dependent inhibition: cells divide to fill a gap and then stop 20 µm 20 µm (a) Normal mammalian cells (b) Cancer cells © 2018 Pearson Education Ltd. Figure 12.19a 20 µm (a) Normal mammalian cells © 2018 Pearson Education Ltd. Figure 12.19b 20 µm (b) Cancer cells © 2018 Pearson Education Ltd. Loss of Cell Cycle Controls in Cancer Cells  Cancer cells do not respond normally to the body’s control mechanisms  Cancer cells do 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 © 2018 Pearson Education Ltd.  Cells that acquire the ability to divide indefinitely are undergoing 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 only at the original site, the lump is called a benign tumor © 2018 Pearson Education Ltd.  Malignant tumors invade surrounding tissues and can undergo metastasis, the spread of cancer cells to other parts of the body, where they may form additional tumors  Localized tumors may be treated with high-energy radiation, which damages the DNA in the cancer cells  To treat metastatic cancers, chemotherapies that target the cell cycle may be used © 2018 Pearson Education Ltd. Figure 12.20 5 µm Breast cancer cell (colorized SEM) Metastatic Lymph tumor vessel Tumor Blood vessel Glandular Cancer tissue cell 1 A tumor grows 2 Cancer cells invade 3 Cancer cells spread 4 A small percentage from a single neighboring tissue. through lymph and of cancer cells may cancer cell. blood vessels to other metastasize to parts of the body. another part of the body. © 2018 Pearson Education Ltd.  Recent advances in understanding the cell cycle and cell cycle signaling have led to advances in cancer treatment  Coupled with the ability to sequence the DNA of cells in a particular tumor, treatments are becoming more “personalized” © 2018 Pearson Education Ltd.