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1/20/2015 Cell Division | Principles of Biology from Nature Education Principles of Biology 32 contents Cell Division Cells have processes for copying and distributing genetic material to daughter cells during division. A timelapse series of images shows cell division in a young embryo. Successive cell divisions of a fertilized egg create a fourcell embryo at the end of this series. In the top row, a fertilized egg divides into two cells and then into four cells. The bottom row shows the same seven micrographs with the cells outlined in red to show how the four cells of the embryo arose from a single fertilized egg. © 2010 Nature Publishing Group Wong, C.C., et al. Noninvasive imaging of human embryos before embryonic genome activation predicts development to the blastocyst stage. Nature Biotechnology 28, 1115–1121 (2010) doi: 10.1038/nbt.1686. Used with permission. Topics Covered in this Module Overview of Cell Division Prokaryotic Cell Division Eukaryotic Cell Division Major Objectives of this Module http://www.nature.com/principles/ebooks/principlesofbiology104015/29155678#bookContentViewAreaDivID 1/2 1/20/2015 Cell Division | Principles of Biology from Nature Education Identify the major phases of the eukaryotic cell cycle and describe the major events that occur during each phase. Explain in detail how mitosis proceeds followed by cytokinesis. Describe how prokaryotes divide by binary fission. page 168 of 989 5 pages left in this module http://www.nature.com/principles/ebooks/principlesofbiology104015/29155678#bookContentViewAreaDivID 2/2 1/20/2015 Cell Division | Principles of Biology from Nature Education Principles of Biology 32 Cell Division contents Overview of Cell Division Cells reproduce. That is, one cell divides into two through a process known as cell division. When a parent cell divides, the two daughter cells are genetically identical (or nearly so) to the parent cell. In multicellular organisms like humans, cell division enables growth and the replacement of wornout or damaged cells. For example, the cells lining the esophagus, the tube that connects the mouth to the stomach, only live for 2 or 3 days before being replaced. Cells may divide to repair injury, as when skin cells grow over a wound or a broken bone knits. Dividing cells in animal embryos, known as stem cells, produce all the specialized cells of the body. Cells divide through one of several methods. Prokaryotes reproduce through binary fission, whereas eukaryotic cells divide through either mitosis or meiosis. During binary fission, bacteria replicate their genetic material (usually a single chromosomelike structure) and grow to a certain size before splitting into two daughter cells. Mitosis is the process in eukaryotes of producing exact copies of the parent cell's chromosomes and segregating them into separate nuclei, followed by cytokinesis to produce two daughter cells. As in binary fission, the two cells produced by mitosis contain all the same parts and largely identical genomes. In contrast, meiosis produces daughter cells that contain half the number of chromosomes of the parent cell; thus, the daughter cells are not exact copies. Meiosis leads to the formation of gametes, which then fuse with another such gamete during sexual reproduction. IN THIS MODULE Overview of Cell Division Prokaryotic Cell Division Eukaryotic Cell Division Summary Test Your Knowledge WHY DOES THIS TOPIC MATTER? Cancer: What's Old Is New Again Is cancer ancient, or is it largely a product of modern times? Can cuttingedge research lead to prevention and treatment strategies that could make cancer obsolete? Synthetic Biology: Making Life from Bits and Pieces Scientists are combining biology and engineering to change the world. Stem Cells Stem cells are powerful tools in biology and medicine. What can scientists do with these cells and their incredible potential? PRIMARY LITERATURE The memory of iPS cells Incomplete DNA methylation underlies a transcriptional memory of somatic cells in human iPS cells. View | Download Geneticallymatched iPS cells more immunogenic than ES cells Immunogenicity of induced pluripotent stem cells. View | Download Adaptor proteins regulate cell signaling Structural basis for regulation of the Crk signaling protein by a proline switch. View | Download The role of cyclin D1 in DNA repair linked to cancer growth A function for cyclin D1 in DNA repair uncovered by protein interactome analyses in human cancers. View | Download SCIENCE ON THE WEB A View Through a Microscope Watch a short video of cell division in different types of cells. A Population of Mitotic Cells http://www.nature.com/principles/ebooks/principlesofbiology104015/29155678/1 1/2 1/20/2015 Cell Division | Principles of Biology from Nature Education Watch cells dividing in a developing embryo, and follow the fluorescently labeled spindles Bacteria Dividing See how bacterial division creates a colony, starting from a few cells Dividing Cancer Cells How long does it take for cancer cells to grow? Choose your time window and watch what happens. page 169 of 989 4 pages left in this module http://www.nature.com/principles/ebooks/principlesofbiology104015/29155678/1 2/2 1/20/2015 Cell Division | Principles of Biology from Nature Education Principles of Biology 32 Cell Division contents Prokaryotic Cell Division Prokaryotes divide by binary fission. The prokaryotic cell copies its genome, increases in size and then splits into two daughter cells. Most bacteria possess just one circular chromosome; there is no nucleus. Although a bacterial genome is much simpler than a eukaryotic genome, it still holds an enormous amount of information that must be copied accurately for the daughter cells to survive. Escherichia coli are bacteria that live in the human gut and many other environments. If stretched out, an E. coli chromosome extends 1,500 times the length of an E. coli cell. Proteins involved in supercoiling DNA accomplish the feat of packaging the E. coli chromosome into a compact structure. To watch replication in action, researchers have used fluorescent molecules that label the origin of replication green, which is the point at which replication of an E. coli chromosome begins. This green region can be viewed through a fluorescent microscope. As the DNA replicates, the labeled region proceeds in opposite directions from a single point of origin until the two replication forks meet and complete duplication of the chromosome. The cell elongates and increases in size. The two copies of the bacterial genome separate and move to opposite ends of the replicating cell or, in some bacteria, different specific places in the cell. Scientists do not fully understand how the chromosomes move or how they are anchored to their new locations. They have identified one protein that appears to help the chromosomes move. Another protein seems to help pinch the plasma membrane together to separate the parent cell into two daughter cells. Other cellular components gather near the point of division to redirect cell wall formation and prevent DNA damage. If the DNA replication finishes without errors, each daughter cell will have the same genome as the parent cell. Do bacteria always reproduce in the same way? Under certain environmental conditions, such as scarce food or danger of drying out, bacteria switch from reproducing by binary fission to using mechanisms that help ensure their survival under these more stressful conditions. In harsh environments, many bacteria produce endospores: dormant forms that can survive under adverse environmental conditions. When nutrients are scarce or the environment becomes particularly harsh, a common soil bacterium called Bacillus subtilis may produce a resilient endospore within the parent vegetative cell that can live for thousands of years. When conditions favor the growth of the species, the endospore germinates, producing a normal bacterium. Other bacteria produce spores as a normal part of their life cycle. Metabacterium polyspora, a bacterium that lives symbiotically in the guinea pig gastrointestinal tract, produces endospores. These endospores pass into an individual's feces, which is then eaten by the animal to extract more nutrients, after which the endospores pass through the stomach and germinate into viable bacteria when they reach the small intestine. Threedimensional microscopy techniques (such as scanning electron microscopy or SEM) can produce images of a cell's surface, which help scientists visualize bacterial reproduction. Certain bacteria reproduce asymmetrically by budding, breaking off daughter cells from the tip of the bacterium or the end of a stalk. In some species, the daughter cell develops immediately into a cell identical to the parent. Other daughter cells enter into a different part of the life cycle. For instance, Pedomicrobium cells are immobile, but they produce flagellated buds that swim away from the parent before maturing into immobile adults. The daughter cells move in search of food and improve their survival by reducing the competition among the newly formed cells. Test Yourself What benefits might mobility provide to Pedomicrobium daughter cells? Submit Can one division create more than two cells? When environmental conditions are stressful, some bacteria undergo multiple fission events; some cyanobacteria always reproduce through multiple fission events. The cyanobacteria Stanieria replicate their DNA but do not notably increase the size of their cytoplasm before cell division. They divide rapidly many times to produce up to 1,000 small cells called baeocytes. The rupture of the multiple cell walls that have formed releases the baeocytes. Streptomyces coelicolor grow underground by extending filaments that break into multiple long cells. When nutrients are depleted, these bacteria extend above ground and release spores into the air. IN THIS MODULE Overview of Cell Division Prokaryotic Cell Division Eukaryotic Cell Division Summary Test Your Knowledge WHY DOES THIS TOPIC MATTER? Cancer: What's Old Is New Again Is cancer ancient, or is it largely a product of modern times? Can cuttingedge research lead to prevention and treatment strategies that could make cancer obsolete? http://www.nature.com/principles/ebooks/principlesofbiology104015/29155678/2 1/2 1/20/2015 Cell Division | Principles of Biology from Nature Education Synthetic Biology: Making Life from Bits and Pieces Scientists are combining biology and engineering to change the world. Stem Cells Stem cells are powerful tools in biology and medicine. What can scientists do with these cells and their incredible potential? PRIMARY LITERATURE The memory of iPS cells Incomplete DNA methylation underlies a transcriptional memory of somatic cells in human iPS cells. View | Download Geneticallymatched iPS cells more immunogenic than ES cells Immunogenicity of induced pluripotent stem cells. View | Download Adaptor proteins regulate cell signaling Structural basis for regulation of the Crk signaling protein by a proline switch. View | Download The role of cyclin D1 in DNA repair linked to cancer growth A function for cyclin D1 in DNA repair uncovered by protein interactome analyses in human cancers. View | Download SCIENCE ON THE WEB A View Through a Microscope Watch a short video of cell division in different types of cells. A Population of Mitotic Cells Watch cells dividing in a developing embryo, and follow the fluorescently labeled spindles Bacteria Dividing See how bacterial division creates a colony, starting from a few cells Dividing Cancer Cells How long does it take for cancer cells to grow? Choose your time window and watch what happens. page 170 of 989 3 pages left in this module http://www.nature.com/principles/ebooks/principlesofbiology104015/29155678/2 2/2 Principles of Biology 32 Cell Division contents Eukaryotic Cell Division Like binary fission, eukaryotic cell division results in two daughter cells that are nearly identical to the parent cell. Importantly, with mitosis, each daughter cell contains the same number of chromosomes as the parent cell. Most eukaryotes have several chromosomes. Humans have 23 pairs, or 46 chromosomes. These chromosomes contain 3 billion nucleotide pairs that would extend 2 m (6.5 feet) if stretched out; more than 250,000 times the length of a single cell. Before cell division, the loosely packed DNA is copied and then condensed into tightly packed chromosomes (Figure 1). Eukaryotic cell division is a complex process. Unlike prokaryotes, a eukaryotic cell contains membrane bound organelles including the nucleus, which must either be divided among or reconstructed within the daughter cells. Figure 1: Condensed human chromosomes. Scanning electron micrograph of several human chromosomes in a condensed form prior to cell division. magnification = 25,000x Biophoto Associates/Science Source. In 1882, the German anatomist Walther Flemming (Figure 2a) first recorded the process of mitosis. Flemming was able to visualize the chromosomes in a single cell using dyes that bound strongly to chromatin, a technique still used by scientists today (Figure 2b). Figure 2: Walther Flemming and his late 19th century illustrations of mitosis. Panel a) Walther Flemming was the first to record the process of mitosis. Panel b) Drawings of mitosis created by Flemming. These drawings inspired many textbook illustrations. a) Science Photo Library/Science Source. b) Illustration from Zellsubstanz, Kern und Zelltheilung. What happens when a cell is not dividing? Using the microscopy techniques of his time, Flemming could determine only that cells grew larger between divisions. Now we know that mitosis is a small part of the cell cycle, the life cycle of a cell from the time it first forms until the time it divides (Figure 3). Mitosis (M phase) alternates with interphase — the phase in which the cell grows and the DNA replicates in preparation for mitosis. Interphase occurs in three subphases: G1 phase (first gap, in which the cell grows), S phase (synthesis, in which the chromosomes are duplicated), and G2 phase (second gap, in which the cell grows more and prepares to begin the process of mitosis). Proteins, organelles, and cytoplasm are produced during the gap phases, but DNA is synthesized only during the S phase. Given the size of most eukaryotic genomes, copying the genome is a major task of the cell cycle. In a human cell that divides once in 24 hours, the S phase lasts 6–8 hours, or almost half of the cell cycle. Mitosis takes less than 1 hour. Cells that divide infrequently spend most of their time either in the G1 phase or in an extended, nondividing phase called G0 phase. Figure 3: The cell cycle. In the cell cycle, interphase includes the G1 , S, and G2 phases. Nondividing cells can remain in interphase indefinitely by entering the G0 phase. The relatively short processes of cell division include mitosis and cytokinesis. © 2012 Nature Education All rights reserved. Figure Detail How does the cell prepare for division? How is the huge amount of DNA in a eukaryotic cell organized? Before and during replication, a cell's DNA is packaged with histone proteins into densely packed fibers, called chromatin. Replication begins at hundreds or even thousands of origin points. During replication, specialized proteins (helicases) unwind the DNA double helix and hold it in place while other enzymes (DNA polymerases) copy the nucleotide sequence. The DNA polymerases constantly proofread the copy and correct copying errors. Once the copies are complete, the chromatin fibers coil tightly and fold into thick chromosomes. The two copies of the same chromosome are paired into sister chromatids. Each pair of sister chromatids are bound together by a DNAprotein complex called the centromere. A nuclear envelope surrounds the duplicated chromosomes. The cell's centrosome, a structure that organizes microtubules during mitosis, duplicates during interphase in an animal cell. The two centrosomes stay together near the nucleus (Figure 4, number 3). How does the cell divide? To make sense of the specific events of cell division, scientists have identified five stages of mitosis, although it is actually a continuous process. These five stages are called prophase, prometaphase, metaphase, anaphase and telophase (Figure 4, numbers 48). Figure 4: The indepth cell cycle. The phases of the cell cycle are delineated by specific events. The M phase (mitosis), where the genetic material is segregated, is further subdivided into prophase, prometaphase, metaphase, anaphase, and telophase. © 2013 Nature Education All rights reserved. Figure Detail During prophase, in most organisms, the chromatin condenses into chromosomes that are visible with a light microscope. At this point, the nucleoli and ribosomes disappear, and the mitotic spindle begins to take shape. The mitotic spindle is a complex structure, consisting of microtubules and associated proteins, that is responsible for organizing the chromosomes and pulling them apart. Although plant cells lack centrosomes, they do form mitotic spindles, which are a crucial organizing force in eukaryotic cell division. In prophase, microtubules connected to the centrosomes grow through the addition of tubulin protein subunits to the ends of the microtubules, lengthening the microtubules and beginning to push the centrosomes apart. During prometaphase, as the chromosomes condense further, kinetochore protein complexes attach to the centromeres that join sister chromatids. The nuclear envelope usually breaks into pieces during prometaphase, allowing the mitotic spindle to extend across the cell and through the nuclear space. Some of the microtubules bind with the kinetochores, thus linking together the centrosomes and the chromosomes (Figure 4, number 5) and setting the stage for the events that occur during metaphase. During metaphase, specialized motor proteins move the chromosomes along microtubules to the middle of the cell. The chromosomal centromeres lie on the imaginary plane of the metaphase plate, stretching across the middle of the cell (Figure 4, number 6). The two kinetochores of each sister chromatid face in opposite directions and are joined by microtubules to the opposing centrosomes. During anaphase, proteins attached to the chromatids are released, causing the sister chromatids to rapidly separate. The newly formed daughter chromosomes move toward opposite ends of the cell, pushed and pulled by motor proteins along the microtubules (Figure 4, number 7). In the final stage of mitosis, telophase, fragments of the parent nuclear membrane and other intracellular membranes join to form a new nuclear envelope around each collection of chromosomes, forming two daughter nuclei. The chromosomes loosen and straighten out to some extent. The microtubules disintegrate, and mitosis is complete (Figure 4, number 8). The stages of mitosis are recapitulated in a series of photomicrographs (Figure 5). Mitosis is the process for distributing the cell's duplicated chromosomes equally. How then is the rest of the cell divided up, ultimately forming two daughter cells? Shortly after mitosis, the cytoplasm finishes dividing through the process of cytokinesis (Figure 4, number 9 and Figure 5, the two rightmost images). In animal cells, cytokinesis begins with a cleavage furrow, a narrow groove in the middle of the dividing cell at the location of the former metaphase plate. Actin microfilaments form a ring around the inside of the cell at the cleavage furrow. The filaments are drawn together, contracting the ring and pinching the cell membrane together. This pinching action separates the cytoplasm into two identical daughter cells. Figure 5: The stages of mitosis and cytokinesis. A series of photomicrographs show an animal cell undergoing mitosis and cytokinesis. magnification = 500x Thomas Deerinck, NCMIR/Science Source. Test Yourself Mitosis focuses on the nucleus. What other cell structures need to be reformed or reorganized in the daughter cells? Submit How is cytokinesis different in plants? Plant cells have cell walls. Instead of a cleavage furrow forming, the Golgi apparatus generates vesicles that move along microtubules to the middle of the cell and join to form a cell plate. Cell wall materials gather within the cell plate, and the plate enlarges until it joins up with the edges of the plasma membrane. The plate separates down the middle, producing a new membrane and cell wall for each daughter cell (Figure 6). Figure 6: Formation of the cell plate. In plants, the cell plate forms between two daughter cells, separating them. The cell plate in this transmission electron micrograph is the bright blue line in the middle of the cell. David M. Phillips/Science Source. Test Yourself Unlike animal cells, the cells of bacteria, plants, fungi and many protists are surrounded by a cell wall. How might this change the process of cytokinesis? Submit Future perspectives. Errors in cell division and the cell cycle can lead to uncontrolled cell growth, which can result in cancer and other disorders. Understanding normal cell division may help scientists and doctors find ways to repair or prevent errors in cell division and the cell cycle. In addition, the human body uses the control of cell division to repair injuries. Knowing when the body can repair itself helps doctors provide patients with prognoses, and knowing how the repair process works may allow scientists to encourage or modulate it. For instance, abnormal formation of new neurons in the adult spinal cord may cause people to feel pain in response to sensations that do not normally cause pain. Transplanting stem cells to the spinal cord may alleviate these symptoms, perhaps because the stem cells are able to properly control cell division. For many years, scientists believed that the neurons in the adult brain did not divide and could not be replaced if they were lost. During the last 20 years, studies have shown that new neurons can form in the adult brain. For instance, antidepressant medications can initiate new neurons to form in the hippocampus, a part of the brain associated with memory. Problems forming new neurons in the hippocampus may increase a person's risk of developing posttraumatic stress disorder (PTSD), a condition marked by difficulty matching cues to contexts. A returning soldier might hear a loud noise in the house and respond as if it were a gunshot, although the context of the familiar setting should make a gunshot unlikely. Stimulating hippocampal neuron development might help this person interpret contexts more accurately. IN THIS MODULE Overview of Cell Division Prokaryotic Cell Division Eukaryotic Cell Division Summary Test Your Knowledge WHY DOES THIS TOPIC MATTER? Cancer: What's Old Is New Again Is cancer ancient, or is it largely a product of modern times? Can cuttingedge research lead to prevention and treatment strategies that could make cancer obsolete? Synthetic Biology: Making Life from Bits and Pieces Scientists are combining biology and engineering to change the world. Stem Cells Stem cells are powerful tools in biology and medicine. What can scientists do with these cells and their incredible potential? PRIMARY LITERATURE The memory of iPS cells Incomplete DNA methylation underlies a transcriptional memory of somatic cells in human iPS cells. View | Download Geneticallymatched iPS cells more immunogenic than ES cells Immunogenicity of induced pluripotent stem cells. View | Download Adaptor proteins regulate cell signaling Structural basis for regulation of the Crk signaling protein by a proline switch. View | Download The role of cyclin D1 in DNA repair linked to cancer growth A function for cyclin D1 in DNA repair uncovered by protein interactome analyses in human cancers. View | Download SCIENCE ON THE WEB A View Through a Microscope Watch a short video of cell division in different types of cells. A Population of Mitotic Cells Watch cells dividing in a developing embryo, and follow the fluorescently labeled spindles Bacteria Dividing See how bacterial division creates a colony, starting from a few cells Dividing Cancer Cells How long does it take for cancer cells to grow? Choose your time window and watch what happens. page 171 of 989 2 pages left in this module 1/20/2015 Summary of Cell Division | Principles of Biology from Nature Education Principles of Biology contents 32 Cell Division Summary OBJECTIVE Identify the major phases of the eukaryotic cell cycle and describe the major events that occur during each phase. The phases of the eukaryotic cell cycle are interphase, mitosis and cytokinesis. Interphase is further divided into G1 when a cell grows, S when the chromosomes are replicated, and G2 when the cell readies itself for cell division by growing and making copies of various cell organelles. The chromosomes are divided equally during mitosis, followed by cytokinesis when the new cell membrane forms around the two new daughter cells. OBJECTIVE Explain in detail how mitosis proceeds followed by cytokinesis. Mitosis is divided into five stages: prophase, prometaphase, metaphase, anaphase, and telophase. During prophase, chromosomes condense and the mitotic spindle begins to take shape. During prometaphase, the nuclear envelope breaks down and the mitotic spindle expands. During metaphase, chromosomes line up in the middle of the cell with sister chromatids facing opposite ends of the cell. During anaphase, sister chromatids separate, and motor proteins move them along microtubules to opposite ends of the cell. During telophase, two new nuclei form, completing mitosis. Shortly after the end of mitosis in animal cells, proteins form a ring around the middle of the cell and tighten into a noose, separating the cytoplasm and cell membranes into two cells. This process is called cytokinesis. OBJECTIVE Describe how prokaryotes divide by binary fission. Prokaryotic cell division commonly occurs by binary fission. This process results in replication of the single circular chromosome and cytoplasm expansion. The cell membrane pinches together to form two new cells, each with a complete genome. Cell division typically results in two daughter cells identical to the parent cell. Under certain conditions, prokaryotes may reproduce using endospores, budding or multiple fission events with little growth between them. Key Terms anaphase Shortest stage of mitosis: proteins of the centromere linking the chromatids cut apart and the sister chromatids separate. binary fission Cell division in prokaryotes where two daughter cells are produced from the parent cell; asexual reproduction in unicellular prokaryotes and eukaryotes. cell cycle Life cycle of a cell; includes interphase, mitosis, and cytokinesis. cell division Reproduction of the cell in which one cell becomes two identical cells. cell plate The precursor for the new cell wall that forms during cytokinesis in plant cells. centromere DNAprotein complex which attaches the two sister chromatids. centrosome Organizes the microtubules of the spindle during mitosis in animals. chromatin DNA and proteins (histones) that make up the chromosomes. chromosome Tightly coiled form of the DNAprotein complex. cleavage furrow During cytokinesis in animals, the contractible ring of microfilaments around the equator of the cell. cytokinesis Division and separation of the cell outside the nucleus. G0 phase Extended, nondividing stage in cells that divide infrequently. G1 phase First gap phase of interphase, when cell growth occurs. G2 phase Second gap phase when the cell continues to grow and prepares for division. interphase Phase of the cell cycle in which the cell grows and the DNA replicates. http://www.nature.com/principles/ebooks/principlesofbiology104015/29155678/4 1/3 1/20/2015 Summary of Cell Division | Principles of Biology from Nature Education kinetochore Protein structure associated with a specific DNA sequence that attaches the chromosome to a fiber of the spindle apparatus. M phase Mitotic phase of the cell cycle. meiosis Type of cell division that produces gametes (in animals) or sexual spores (in fungi and plants) that have half the genetic material of the parent cell. metaphase Stage of mitosis in which motor proteins move the chromosomes to align along the equator of the cell. metaphase plate An imaginary plane located at right angles to the mitotic spindle and midway between the spindle poles, where chromosomes are positioned at metaphase. mitosis Type of cell division which results in two genetically identical cells. mitotic spindle Microtubules and associated proteins that attach to and move the chromosomes during cell division. motor proteins Proteins that convert the energy of ATP into movement along a surface. During mitosis and cytokinesis, motor proteins move along microtubules and actin microfilaments facilitating the movement of things like chromosomes. prometaphase Stage of mitosis in which chromosomes condense further and attach to the spindle via the kinetochore. prophase Stage of mitosis in which the DNA condenses and chromosomes become visible. S phase Synthesis phase of interphase when the chromosomes are duplicated. sister chromatid One of a pair of chromatin threads; one side of a chromosome Xshape. supercoiling A process of compacting DNA inside a cell by twisting it around itself. telophase Stage of mitosis in which the nuclei reform and the chromosomes uncoil; microtubules make the spindle dissociate. tubulin The building blocks or subunits of microtubules. IN THIS MODULE Overview of Cell Division Prokaryotic Cell Division Eukaryotic Cell Division Summary Test Your Knowledge WHY DOES THIS TOPIC MATTER? Cancer: What's Old Is New Again Is cancer ancient, or is it largely a product of modern times? Can cuttingedge research lead to prevention and treatment strategies that could make cancer obsolete? Synthetic Biology: Making Life from Bits and Pieces Scientists are combining biology and engineering to change the world. Stem Cells Stem cells are powerful tools in biology and medicine. What can scientists do with these cells and their incredible potential? PRIMARY LITERATURE The memory of iPS cells Incomplete DNA methylation underlies a transcriptional memory of somatic cells in human iPS cells. View | Download http://www.nature.com/principles/ebooks/principlesofbiology104015/29155678/4 2/3 1/20/2015 Summary of Cell Division | Principles of Biology from Nature Education Geneticallymatched iPS cells more immunogenic than ES cells Immunogenicity of induced pluripotent stem cells. View | Download Adaptor proteins regulate cell signaling Structural basis for regulation of the Crk signaling protein by a proline switch. View | Download The role of cyclin D1 in DNA repair linked to cancer growth A function for cyclin D1 in DNA repair uncovered by protein interactome analyses in human cancers. View | Download SCIENCE ON THE WEB A View Through a Microscope Watch a short video of cell division in different types of cells. A Population of Mitotic Cells Watch cells dividing in a developing embryo, and follow the fluorescently labeled spindles Bacteria Dividing See how bacterial division creates a colony, starting from a few cells Dividing Cancer Cells How long does it take for cancer cells to grow? Choose your time window and watch what happens. page 172 of 989 1 pages left in this module http://www.nature.com/principles/ebooks/principlesofbiology104015/29155678/4 3/3 1/20/2015 Cell Division | Principles of Biology from Nature Education Principles of Biology contents 32 Cell Division IN THIS MODULE Overview of Cell Division Test Your Knowledge Prokaryotic Cell Division Eukaryotic Cell Division 1. Under favorable environmental conditions, how do most prokaryotes reproduce? Summary Test Your Knowledge meiosis mitosis endospores budding binary fission WHY DOES THIS TOPIC MATTER? Cancer: What's Old Is New Again Is cancer ancient, or is it largely a product of modern times? Can cuttingedge research lead to prevention and treatment strategies that could make cancer obsolete? 2. How does cytokinesis begin in an animal cell? Actin forms a ring outside the cell membrane. Vesicles move to the middle of the cell. Chromosomes line up across the middle of the cell. A cell plate forms. A cleavage furrow forms. Synthetic Biology: Making Life from Bits and Pieces Scientists are combining biology and engineering to change the world. Stem Cells Stem cells are powerful tools in biology and medicine. What can scientists do with these cells and their incredible potential? 3. What is the role of centrosomes in mitosis? holding together the two sister chromatids organizing the microtubules that form the mitotic spindle acting as an attachment point between microtubules and chromosomes proofreading DNA producing RNA and ribosomes PRIMARY LITERATURE The memory of iPS cells Incomplete DNA methylation underlies a transcriptional memory of somatic cells in human iPS cells. View | Download 4. Without the mitotic spindle, how would mitosis be different? Geneticallymatched iPS cells more immunogenic than ES cells Immunogenicity of induced pluripotent stem cells. View | Download The cell membrane would not form around daughter nuclei. Crossing over would not occur, so genes would more often segregate independently. Sister chromatids would have to physically segregate by some other means. More mistakes would occur during DNA replication. DNA synthesis would be incomplete. Adaptor proteins regulate cell signaling Structural basis for regulation of the Crk signaling protein by a proline switch. View | Download 5. How is DNA arranged in a eukaryotic cell during the G1 phase of interphase? The role of cyclin D1 in DNA repair linked to cancer growth A function for cyclin D1 in DNA repair uncovered by protein interactome analyses in human cancers. View | Download in pairs of sister chromatids in plasmids by microtubule length in chromatin fibers in condensed chromosomes SCIENCE ON THE WEB A View Through a Microscope Watch a short video of cell division in different types of cells. 6. In which phase does a normal cell make the commitment to divide or not? G1 M G2 S None of these answers are correct. A Population of Mitotic Cells Watch cells dividing in a developing embryo, and follow the fluorescently labeled spindles Bacteria Dividing See how bacterial division creates a colony, starting from a few cells 7. Which of the following steps of mitosis occurs first in plants and animals? Dividing Cancer Cells How long does it take for cancer cells to grow? Choose your time window and watch what happens. The DNA replicates. Chromatids line up in the middle of the cell. The nuclear membrane breaks apart. Sister chromatids separate. The cell membrane pinches together in the middle. Submit page 173 of 989 http://www.nature.com/principles/ebooks/principlesofbiology104015/29155678/5 1/1