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Chapter 12 The Cell Cycle PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Cellular Growth Ratio of Surface Area to Volume Cellular Growth As the cell grows, its volume increases much more rapidly than the surface area. The cell might have difficulty supplying nutrients and expelling enough waste products. Cellular Growth Transport of Substances Substances move by diffusion or by motor proteins. Diffusion over large distances is slow and inefficient. Small cells maintain more efficient transport systems. Cellular Growth Cellular Communications The need for signaling proteins to move throughout the cell also limits cell size. Cell size affects the ability of the cell to communicate instructions for cellular functions. Cellular Growth The Cell Cycle Cell division prevents the cell from becoming too large. It also is the way the cell reproduces so that you grow and heal certain injuries. Cells reproduce by a cycle of growing and dividing called the cell cycle. 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 12-2a 100 µm (a) Reproduction Fig. 12-2b 200 µm (b) Growth and development Fig. 12-2c 20 µm (c) Tissue renewal Concept 12.1: Cell division results in genetically identical daughter cells Most cell division results in daughter cells with identical genetic information, DNA A special type of division produces nonidentical daughter cells (gametes, or sperm and egg cells) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 12-3 chromatin 20 µm Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus Somatic cells (nonreproductive cells) have two sets of chromosomes (diploid number) Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells (haploid number) Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein that condenses during cell division 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, which separate during cell division The centromere is the narrow “waist” of the duplicated chromosome, where the two chromatids are most closely attached Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 12-4 0.5 µm Chromosomes Chromosome arm DNA molecules Chromosome duplication (including DNA synthesis) Centromere Sister chromatids Separation of sister chromatids Centromere Sister chromatids Cellular Growth Interphase is the stage during which the cell grows, carries out cellular functions, and replicates. Mitosis is the stage of the cell cycle during which the cell’s nucleus and nuclear material divide. Cytokinesis is the method by which a cell’s cytoplasm divides, creating a new cell. Cellular Growth The Stages of Interphase The first stage of interphase, G1 The cell is growing, carrying out normal cell functions, and preparing to replicate DNA. Cellular Growth The Second Stage of Interphase, S The cell copies its DNA in preparation for cell division. Cellular Growth The Third Stage of Interphase, G2 The cell prepares for the division of its nucleus. Interphase occurs before mitosis begins • • Chromosomes are copied (# doubles) Chromosomes appear as threadlike coils (chromatin) at the start, but each chromosome and its copy(sister chromosome) change to sister chromatids at end of this phase •Nucleus •CELL MEMBRANE •Cytoplasm Interphase •Animal Cell •Plant Cell •Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Prophase 1st step in Mitosis • Mitosis begins (cell begins to divide) • Centrioles (or poles) appear and begin to move to opposite end of the cell. • Spindle fibers form between the poles. •Sister chromatids •Centrioles •Spindle fibers The mitotic spindle is an apparatus of microtubules that controls chromosome movement during mitosis During prophase, assembly of spindle microtubules begins in the centrosome, the microtubule organizing center The centrosome replicates, forming two centrosomes that migrate to opposite ends of the cell, as spindle microtubules grow out from them An aster (a radial array of short microtubules) extends from each centrosome • The spindle includes the centrosomes, the spindle microtubules, and the asters Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Prophase •Animal Cell •Plant Cell •Spindle fibers •Centrioles •Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Metaphase 2nd step in Mitosis • Chromatids (or pairs of chromosomes) attach to the spindle fibers. •Centrioles •Spindle fibers Metaphase •Animal Cell •Plant Cell •Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Anaphase 3rd step in Mitosis • Chromatids (or pairs of chromosomes) separate and begin to move to opposite ends of the cell. •Centrioles •Spindle fibers Anaphase •Animal Cell •Plant Cell •Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Telophase 4th step in Mitosis • Two new nuclei form. • Chromosomes appear as chromatin (threads rather than rods). • Mitosis ends. •Nuclei •Chromatin •Nuclei Telophase •Animal Cell •Plant Cell •Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Cytokinesis occurs after mitosis • Cell membrane moves inward to create two daughter cells – each with its own nucleus with identical chromosomes. •Animal Mitosis -- Review Interphase Prophase Metaphase Anaphase Telophase Interphase •Plant Mitosis -- Review Interphase Prophase Metaphase Anaphase Telophase Interphase 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 Which we already talked about Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 12-8 EXPERIMENT Kinetochore Spindle pole Mark RESULTS CONCLUSION Chromosome movement Kinetochore Motor Microtubule protein Chromosome Tubulin subunits Fig. 12-8a EXPERIMENT Kinetochore Spindle pole Mark RESULTS Fig. 12-8b CONCLUSION Chromosome movement Kinetochore Microtubule Motor protein Chromosome Tubulin Subunits Binary Fission 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), the two origins move to opposite sides of the cell and the two daughter chromosomes actively move apart No mitosis is involved Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 12-11-1 Cell wall Origin of replication E. coli cell Two copies of origin Plasma membrane Bacterial chromosome Fig. 12-11-2 Cell wall Origin of replication E. coli cell Two copies of origin Origin Plasma membrane Bacterial chromosome Origin Fig. 12-11-3 Cell wall Origin of replication E. coli cell Two copies of origin Origin Plasma membrane Bacterial chromosome Origin Fig. 12-11-4 Cell wall Origin of replication E. coli cell Two copies of origin Origin Plasma membrane Bacterial chromosome Origin The Evolution of Mitosis Since 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 12-12 Bacterial chromosome •Mechanism not known (a) Bacteria Chromosomes •dinoflagellatesCs attach to Microtubules •the nuclear •Membrane; microtubules Intact nuclear envelope (b) Dinoflagellates •Pass through the nucleus; •Then cell divides •Diatoms and yeast Kinetochore microtubule •Microtubules form •Within the cell (not Intact nuclear envelope •The nucleus into the •Cytosol like in (c) Diatoms and yeasts •flagellates Kinetochore microtubule Fragments of nuclear envelope (d) Most eukaryotes •eukaryotes 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 cell cycle differences result from regulation at the molecular level Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Evidence for Cytoplasmic Signals 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 12-13 EXPERIMENT Experiment 1 S G1 Experiment 2 M G1 RESULTS S S When a cell in the S phase was fused with a cell in G1, the G1 nucleus immediately entered the S phase—DNA was synthesized. M M When a cell in the M phase was fused with a cell in G1, the G1 nucleus immediately began mitosis—a spindle formed and chromatin condensed, even though the chromosome had not been duplicated. 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Cell Cycle Regulation Normal Cell Cycle Different cyclin/CDK (cyclin-dependent kinases) combinations signal other activities, including DNA replication, protein synthesis, and nuclear division throughout the cell cycle. MPF (maturation-promoting factor) is a cyclin-Cdk complex that triggers a cell’s passage past the G2 checkpoint into the M phase Cell Cycle Regulation Quality Control Checkpoints The cell cycle has built-in checkpoints that monitor the cycle and can stop it if something goes wrong. Spindle checkpoints also have been identified in mitosis. • For many cells, the G1 checkpoint seems to be the most important one • 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 12-15 G0 G1 checkpoint G1 (a) Cell receives a go-ahead signal G1 (b) Cell does not receive a go-ahead signal Stop and Go Signs: Internal and External Signals at the Checkpoints An example of an internal signal is that kinetochores not attached to spindle microtubules send a molecular signal that delays anaphase until they all have attached; making sure that the cell doesn’t divide until it has all its parts Some external signals are growth factors, proteins released by certain cells that stimulate other cells to divide For example, platelet-derived growth factor (PDGF) stimulates the division of human fibroblast cells in culture Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Another example of external signals is density-dependent inhibition, in which crowded cells stop dividing Most animal cells also exhibit anchorage dependence, in which they must be attached to a substratum in order to divide Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 12-19 Anchorage dependence then they will grow Density-dependent inhibition when the cells touch Density-dependent inhibition 25 µm 25 µm (a) Normal mammalian cells (b) Cancer cells Loss of Cell Cycle Controls in Cancer Cells Cancer cells exhibit neither density-dependent inhibition nor anchorage dependence 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings A normal cell is converted to a cancerous cell by a process called transformation Cancer cells 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 metastasize, exporting cancer cells to other parts of the body, where they may form secondary tumors Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 12-20 Lymph vessel Tumor Blood vessel Cancer cell Metastatic tumor Glandular tissue 1 A tumor grows from a single cancer cell. 2 Cancer cells invade neighboring tissue. 3 Cancer cells spread to other parts of the body. 4 Cancer cells may survive and establish a new tumor in another part of the body. You should now be able to: 1. Describe the structural organization of the prokaryotic genome and the eukaryotic genome 2. List the phases of the cell cycle; describe the sequence of events during each phase 3. List the phases of mitosis and describe the events characteristic of each phase 4. Draw or describe the mitotic spindle, including centrosomes, kinetochore microtubules, nonkinetochore microtubules, and asters Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 5. Compare cytokinesis in animals and plants 6. Describe the process of binary fission in bacteria and explain how eukaryotic mitosis may have evolved from binary fission 7. Explain how the abnormal cell division of cancerous cells escapes normal cell cycle controls 8. Distinguish between benign, malignant, and metastatic tumors Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings