Topic 10: Cell Cycle Part A PDF

Topic 10 Cell Reproduction: The Cell Cycle PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Learning objectives (LOBs) Part A (2 sessions): Th...

Topic 10 Cell Reproduction: The Cell Cycle PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Learning objectives (LOBs) Part A (2 sessions): The Cell Cycle 1. Explain cell division and its role in unicellular vs multicellular organisms. 2. Describe the different stages of the cell cycle, including the different stages of mitosis. Part B (2 sessions): Cell cycle regulation (Dr Constantinou) 3. Describe cell cycle control through the checkpoints, including the role of cyclin-cdks, the tumour suppressor genes Rb and p53, and cdk inhibitors (CKIs) in cell cycle regulation. 4. Describe the characteristics of cancer cells related to cell cycle dysregulation, including the difference between benign and malignant tumours. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Recommended reading Reading: Chapter 12, Campbell Biology. Additional reading: Chapter 17, Alberts, B. et al, Molecular Biology of the Cell (2008) 5th Ed. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Cell division Cell division: the reproduction of cells The continuity of life is based upon cell division Role of cell division: Unicellular organisms: Reproduction by cell division (e.g. binary fission) Multicellular organisms depend on cell division for: – Growth – Development from a fertilized cell – Repair of damaged tissues Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Cell division In unicellular organisms In multicellular organisms 100 µm 200 µm 20 µm (b) Growth and development. (c) Tissue renewal. These dividing (a) Reproduction. An amoeba, This micrograph shows an a single-celled eukaryote, is bone marrow cells (arrow) will embryo shortly give rise to new blood cells (LM). dividing into two cells. Each after the fertilized egg divided, new cell will be an individual forming two cells (LM). organism (LM). Figure 12.2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Cell division Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Cell division processes in humans Cell division processes: – Mitosis: production of somatic cells (diploid cells) – Meiosis: production of gametes (haploid cells) Mitosis: conserves the chromosome number of the cells => production of 2 genetically identical cells that are also genetically identical to the parental cell Meiosis: reduces the chromosome number in half => production of gametes in the gonads => Fertilization: A male and female gamete (haploid cells) fuse producing a zygote with a complete set of chromosomes (diploid) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Cell division and the Cell Cycle Why do we need to learn about cell division and understand the Cell Cycle? Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  What is cancer? Cancer is an abnormal growth of cells which tend to proliferate in an uncontrolled way and, in some cases, to metastasize (spread). Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Daughter cell 1 Parent cell Daughter cell 2 Cell division has to be tightly controlled to avoid uncontrolled cell division which leads to carcinogenesis  Cancer: uncontrolled cell growth In order to understand how cancer develops we need to understand how the Cell Cycle works Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Cell cycle Mitosis (cell division process) is an integral part of the cell cycle Mitosis results in 2 genetically identical daughter cells Cells duplicate their genetic material before they divide (DNA replication) => Each daughter cell receives an exact copy of the genetic material (DNA) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Cell cycle The functional process that a cell goes through until it is divided in 2 identical daughter cells Phases (stages) of the cell cycle: - G1 (gap 1): preparation of the cell for DNA replication - S phase (synthesis): DNA replication - G2 (gap 2): preparation for cell division - M phase (mitotic phase): cell division (mitosis) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Phases of the Cell Cycle The cell cycle consists of: – Interphase: G1, S and G2 phases – Mitotic phase: Mitosis and Cytokinesis INTERPHASE S G1 (DNA synthesis) G2 Figure 12.5 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  The phases of the Cell Cycle Interphase: G1, S, G2 M phase: - Mitosis (Prophase, Prometaphase, Metaphase, Anaphase, Telophase) - Cytokinesis Figure 8.3b The Biology of Cancer (© Garland Science 2007)  Cell Cycle phases G0 phase G1 phase S phase interphase Division Mitotic phase G2 phase Daughter cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  G0 phase G0 = quiescent phase - Resting phase: non-dividing cells are resting at this phase Differentiated cells enter from G0 to G1 after the action of growth factors Cells exit G1 and enter G0 (G1 → G0) in order to differentiate Cell cycle control: - Εxtracellular signals (e.g. presence of growth factors) - Intracellular signals (e.g. cell size) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Cell types according to their cell division potential Post-mitotic cells: terminally differentiated cells which have lost their ability to replicate => permanently arrested at G0 phase - Example: neural cells, cardiac muscle cells, red blood cells Cells that divide upon appropriate stimulation (signal): - Example: most of the cells in our body only divide upon stimulation by growth factors or other signal - e.g. lymphocytes upon antigenic presentation Cells with high mitotic activity: e.g. germ cells, stem cells, epithelial cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Interphase The period between cell divisions The larger phase of the cell cycle The cell prepares for cell division Includes the 3 first phases of the cell cycle: - G1, S, G2 phases - Includes DNA replication (S phase) The cell decides whether or not it will proceed with cell division Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Interphase Before cell division (during interphase): 1. Cell components have to replicate (organelles, membranes, proteins) 2. Chromosomes need to replicate Genetic material needs to replicate in order for daughter cells to have the same genome as the parental cell This ensures their survival Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Interphase Interphase can be divided into 3 sub-phases: G1 phase: preparation for DNA replication - Protein synthesis, organelle production - Duration: 5-6 h S phase: DNA synthesis (replication) - Duration: 10-12 h G2 phase: preparation for cell division (mitosis) - Protein synthesis, organelle production - Duration: 4-6 h Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Cellular Organization of the Genetic Material Genome: the complete set of genetic information (DNA) of a cell (all the genes) The DNA molecules of a cell are packaged into chromosomes Eukaryotic chromosomes: – Consist of chromatin, a complex of DNA and proteins (histones) – Each chromosome carries a few hundred to a few thousand genes Chromosomes are huge: A human cell’s DNA is about 2 m long!!! Figure 12.3 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 50 µm  Chromosomal content of human cells 2 types of cells according to their chromosomal content in humans: Somatic cells: diploid cells (2n, n =23 chromosomes) - have 2 sets of 23 chromosomes = 46 total => 23 chromosome pairs - Each homologous chromosome pair has 1 paternal and 1 maternal chromosome Gametes (reproductive cells): haploid cells (n, n =23 chromosomes) – have one set of chromosomes = 23 total – Have only 1 chromosome (either paternal or maternal) from each homologous chromosome pair Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Chromosomal content of human somatic cells Homologous chromosomes: carry the same genes at the same positions Pair of homologous Human Karyotype chromosomes Maternal Paternal chromosome chromosome Each somatic cell has 46 chromosomes (23 chromosome pairs) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Distribution of Chromosomes During Cell Cycle Interphase: chromosomes are not condensed – G1 phase: each chromosome consists of one chromatid (not replicated yet) – S phase: DNA is replicated – G2 phase: Each duplicated chromosome has 2 sister chromatids Mitosis (cell division): - the chromosomes condense => can be seen with a light microscope - sister chromatids separate => each future daughter cell receives one chromatid Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Duplication of chromosomes during cell division 0.5 µm G1 Before duplication, each phase chromosome has a single DNA molecule. Chromosome duplication (including DNA Once duplicated, a chromosome synthesis) S consists of two sister chromatids Centromere phase connected at the centromere. Each chromatid contains a copy of the DNA molecule. Sister Separation chromatids of sister Mechanical processes separate chromatids Mitosis the sister chromatids into two chromosomes and distribute them to two daughter cells. Figure 12.4 Centromeres Sister chromatids Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Cell cycle: DNA content during cell cycle phases Daughter cells (2n) Chromosome condensation Nuclear envelope degradation Cell division Chromosome separation 10-24 hours interphase 4n 2n= diploid cells DNA synthesis 4n=tetraploid cells 2n 27 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  The Mitotic phase (M phase) The Mitotic phase (M phase) consists of: – Mitosis: division of the nucleus – Cytokinesis: division of the cytoplasm Mitosis consists of 5 phases: 1. Prophase 2. Prometaphase 3. Metaphase 4. Αnaphase 5. Τelophase Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Mitosis consists of five distinct phases Figure 12.6 G2 OF INTERPHASE 1. PROPHASE 2. PROMETAPHASE Centrosomes Aster Fragments Kinetochore (with centriole pairs) Chromatin Early mitotic Centromere of nuclear (duplicated) spindle envelope Nonkinetochore microtubules Nucleolus Nuclear Plasma Chromosome, consisting Kinetochore envelope membrane of two sister chromatids microtubule Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Mitosis consists of five distinct phases 3. METAPHASE 4. ANAPHASE 5. TELOPHASE AND CYTOKINESIS Metaphase plate Cleavage Nucleolus furrow forming Nuclear envelope Spindle Daughter forming Centrosome at Figure 12.6 one spindle pole chromosomes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Mitosis phases summary G2 of Interphase Prophase Prometaphase Metaphase Anaphase Telophase and Cytokinesis Centrosomes Chromatin Early mitotic Aster Centromere Fragments Nonkinetochore Metaphase Cleavage Nucleolus (with centriole (duplicated) spindle of nuclear microtubules plate furrow forming pairs) envelope Daughter Nuclear Nucleolus Nuclear Plasma Chromosome, consisting Kinetochore Kinetochore Spindle Centrosome at chromosomes one spindle pole envelope envelope membrane of two sister chromatids microtubule forming https://www.youtube.com/watch?v=VlN7K1-9QB0 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  1. Prophase Prophase Early mitotic Aster Centromere spindle Prophase Chromosome, consisting of two sister chromatids The chromatin fibers condense into distinct chromosomes The nucleoli disappear, nuclear membrane degradation begins The mitotic spindle (composed of centrosomes and microtubules) begins to form Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  2. Prometaphase Prometaphase Fragments Nonkinetochore of nuclear microtubules envelope Prometaphase Kinetochore Kinetochore microtubule The nuclear envelope fragments The microtubules extending from each centrosome can invade the nuclear area and bind to the chromosomes The chromosomes become more condensed Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  3. Metaphase Metaphase Metaphase plate Metaphase Spindle Centrosome at one spindle pole The centrosomes are now at opposite poles The chromosomes are aligned on the metaphase plate (imaginary plane equidistant between the spindle’s two poles) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  4. Anaphase Anaphase Anaphase Daughter chromosomes The sister chromatids of each chromosome move towards opposite poles By the end of anaphase the two poles of the cell have equivalent collections of chromosomes (chromatids) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  5. Telophase Telophase and Cytokinesis Cleavage Nucleolus furrow forming Telophase and Cytokinesis Nuclear envelope forming Nuclear envelops reform Nucleoli reappear Two daughter nuclei form in the cell Chromosomes decondense Mitosis (the division of one nucleus into two genetically identical nuclei) is now complete Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  6. Cytokinesis Telophase and Cytokinesis Cleavage Nucleolus furrow forming Telophase and Cytokinesis Nuclear envelope forming Cytokinesis: the cells are completely separated. The division of the cytoplasm usually begins by late telophase so the two daughter cells appear shortly after the end of mitosis. In animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Chromosomal/DNA content during cell cycle 2n chromosomes G1 phase 2n chromatids (2n) Diploid (2n) DNA replication 2n chromosomes S phase 4n chromatids G2 phase (4n) Tetraploid Mitotic (4n) spindle chromatids 2n chromosomes Metaphase Tetraploid 4n chromatids cell (4n) 4n chromosomes Anaphase 4n chromatids cell Tetraploid (4n) cytokinesis 2n chromosomes 2n chromatids Daughter cells (2n) Diploid (2n) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  1. Prophase 1. Chromosomal condensation: - Interphase: the chromosomes are decondensed (loose form of chromatin) => to help replication and transcription - Μitosis: chromosomal condensation => begins at prophase - Prophase: each chromosome consists of 2 sister chromatids (it is duplicated) - Sister chromatids = DNA copies (replicated during S phase) - sister chromatids are joined by centromeres - Centromeres: consist of repetitive DNA sequences Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  1. Prophase 2. Centrosomes move towards the opposite poles of the cell - Usually found next to the nucleus (cell center) - Centrosome replication: during S phase  2 new centrosomes during mitosis  After mitosis: 1 centrosome per cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  1. Prophase 3. Mitotic spindle formation: - Mitotic spindle begins to form by the polymerisation of microtubules - Microtubule polymerisation starts from the centrosome - Κinetochores: protein structures found at the centromere of each chromosome - 1 kinetochore/chromatid - mitotic spindle microtubules attach to the kinetochores of the chromatids => move chromosomes towards the metaphase plate - Attachment point for motor proteins Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Κinetochore centromere kinetochore Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Κinetochores Kinetochore microtubule Centromere Motor heterochromatin proteins Internal part external part (attachment to kinetochore microtubules) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  1. Prophase 3 types of mitotic spindle microtubules : (a) Αstral microtubules: - radial (star-like) structure around the centrosome - Function: positioning of the spindle in the cell (b) Kinetochore (chromosomal) microtubules: - join the centrosome with the kinetochores (centromeres) of the chromosomes - Function: chromosomal movement (c) Polar microtubules: - start from the centrosome but do not attach to the chromosomes - interact with other polar microtubules projecting from the other pole - Function: maintain the integrity of the spindle Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Microtubule types in mitotic spindle centrosome Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  The Mitotic Spindle The mitotic spindle: - an apparatus of microtubules that controls chromosome movement during mitosis - arises from the centrosomes or other MTOC - includes spindle microtubules (kinetochore and polar) and astral microtubules Animal cells: MTOC= centrosome made by two centrioles Plant cells: have different type of MTOC (lack centrioles) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Centrosome: 2 centrioles Centriole structure: made from microtubules Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Centrosome replication cycle G1 phase S phase mitosis Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  1. Prophase 4. Nuclear envelope and organelle degradation: - Nuclear lamin phosphorylation (nuclear envelope components) - Lamins: intermediate filaments present in the nuclear lamina  Nuclear envelope degradation and packaging into vesicles - Endoplasmic reticulum and Golgi apparatus are also degraded and packaged into vesicles => they will later be separated into the daughter cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  1. Prophase: nuclear envelope degradation Nuclear lamina Nuclear pore chromatin Nuclear envelope Phosphorylated lamin dimer Lamin tetramere Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  2. Prometaphase Begins upon completion of nuclear envelope degradation 1. Chromosomes attach to the spindle microtubules  each chromosome is connected to both poles  One chromatid has orientation towards one pole and the other chromatid towards the other pole 2. Chromosomes move towards the cell center (metaphase plate) - By polymerisation/depolymerisation of kinetochore microtubules Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  2. Prometaphase fast polymerisation fast depolymerisation slow depolymerisation slow depolymerisation Polymerisation Depolymerisation overall pole pole overall chromosome microtubule Slow depolymerisation slow Slow depolymerisation polymerisation pole pole microtubule kinetochore Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  3. Metaphase Chromosomes align in the equatorial plane (metaphase plate) Μetaphase plate = imaginary plane equidistant between the spindle’s two poles If the chromosomes are not aligned correctly => Cell cycle arrest signal Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  3. Metaphase Aster Centrosome Sister Metaphase chromatids Plate Kinetochores Overlapping nonkinetochore microtubules Kinetochore microtubules 0.5 µm Microtubules Chromosomes Figure 12.7 Centrosome 1 µm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  4. Anaphase 1. Sister chromatids separation – Due to inactivation of centromere proteins holding the two chromatids together 2. Sister chromatids move along the kinetochore microtubules towards opposite ends of the cell Kinetochore Spindle pole Figure 12.8 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  4. Anaphase 1. Αnaphase Α: depolymerisation of microtubules - tubulin depolymerisation  chromosomes start moving toward the poles of the spindle  Motor proteins at the kinetochore involved in this process 2. Anaphase Β: separation of the 2 poles (spindle elongation) - Non-kinetochore microtubules from opposite poles overlap and push against each other elongating the cell - Motor proteins involved in this process Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  5. Τelophase Genetically identical daughter nuclei form at the opposite poles of the cell 1. Chromosomes transferred at the opposite poles of the cell (end of anaphase/beginning of telophase) 2. Reformation of the nuclear envelope upon vesicle fusion around the chromosomes 3. Reformation of ER and Golgi apparatus Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  6. Cytokinesis The cytoplasm divides into 2 daughter cells (cytokinesis) Cytokinesis in animal Cleavage furrow cells: 100 µm - occurs by a process known as cleavage, forming a cleavage furrow Contractile ring of Daughter cells microfilaments - Contractile ring Figure 12.9 A (a) Cleavage of an animal cell (SEM) formation: a ring of actin and myosin microfilaments that contracts Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  6a. Cytokinesis in animal cells actin filaments Contractile ring Myosin filaments Cleavage furrow Daughter cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  6b.Cytokinesis: plant cells Cytokinesis in plant cells: involves a cell plate formation Vesicles containing cell wall materials arrive from Golgi to the metaphase plate Cell plate formation from vesicle fusion Vesicles Wall of 1 µm forming parent cell Cell plate New cell wall Cell plate elongates and cell plate fuses with the cell wall of the parental cell Daughter cells Figure 12.9 B (b) Cell plate formation in a plant cell (SEM) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Mitosis in a plant cell (onion root tip) Nucleus Chromatine Chromosome Nucleolus condensing Metaphase. The 1 Prophase. 2 Prometaphase. 3 Anaphase. The 5 Telophase. Daughter The chromatin We now see discrete spindle is complete, 4 chromatids of each nuclei are forming. is condensing. chromosomes; each and the chromosomes, chromosome have Meanwhile, cytokinesis The nucleolus is consists of two attached to microtubules separated, and the has started: The cell beginning to identical sister at their kinetochores, daughter chromosomes plate, which will disappear. chromatids. Later are all at the metaphase are moving to the ends divided the cytoplasm Although not in prometaphase, the plate. of cell as their in two, is growing yet visible nuclear envelop will kinetochore toward the perimeter in the micrograph, fragment. microtubles shorten. of the parent cell. the mitotic spindle is starting to form. Figure 12.10 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Prokaryotic replication: Binary Fission Prokaryotes (bacteria) do not have an organized reproductive cell cycle => do not reproduce by mitosis Prokaryotes reproduce by another type of cell division called binary fission Binary fission is a very simple cell division process => much faster than eukaryotic cell cycle – bacterial replication time is 1-3 h In binary fission: – The bacterial chromosome replicates – The two daughter chromosomes actively move apart Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Binary Fission Origin of Cell wall replication 1 Chromosome replication Plasma begins. Membrane E. coli cell Soon thereafter, one copy Bacterial Two copies Chromosome of the origin moves rapidly of origin toward the other end of the cell. 2 Replication continues. One copy of Origin Origin the origin is now at each end of the cell. 3 Replication finishes. The plasma membrane grows inward, and new cell wall is deposited. Figure 12.11 4 Two daughter cells result. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  The Evolution of Mitosis Since prokaryotes preceded eukaryotes by billions of years – It is likely that mitosis evolved from bacterial cell division Cell division of unicellular eukaryotes: - Certain protists exhibit types of cell division that seem intermediate between binary fission and mitosis carried out by most eukaryotic cells (e.g. multiple fission) Example: replication of Plasmodium malariae (protist) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Summary (part A) Role of cell division (in unicellular vs multicellular organisms) Cell cycle stages: G1 phase: preparation for DNA replication S phase: DNA replication G2 phase: preparation for cell division (mitosis) M phase: cell division (mitosis) G0: Non-dividing cells Mitotic phase: Mitosis: division of nucleus (Prophase, prometaphase, metaphase, anaphase, telophase) Cytokinesis: division of cytoplasm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  SBA example At which cell cycle phase do the cells prepare for DNA replication? A. G0 phase B. G1 phase C. S phase D. G2 phase E. M phase Cell cycle stages: https://www.youtube.com/watch?v=g7iAVCLZWuM Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings