Cell Cycle

10 Key excerpts on "Cell Cycle"

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  eBook - PDF

  Cell Biology and Genetics

  • Rathoure, Ashok Kumar(Authors)
  • 2021(Publication Date)
  • Daya Publishing House

    (Publisher)

  Other fields focus primarily on the mechanical processes of cell cleavage into two daughter cells at the end of mitosis and on the condensation and decondensation of chromatin. Originally, Cell Cycle studies were the preserve of microscopy, but today many specific techniques in addition to those widely employed in cell and molecular biology are applied. Fluorescence activated cell sorting has allowed biologists to both identify cells at particular points of the Cell Cycle and isolate them. It is possible to monitor how cells that have been exposed to different agents can progress through the cycle. Cell division is a very important process in all living organisms. During the division of a cell, DNA replication and cell growth also take place. All these processes i.e . cell division, DNA replication, and cell growth, hence, have to take place in a coordinated way to ensure correct division and formation of progeny cells containing intact genomes. The sequence of events by which a cell duplicates its genome, synthesises the other constituents of the cell and eventually divides into two daughter cells is termed Cell Cycle. Although, cell growth (in terms of cytoplasmic increase) is a continuous process, DNA synthesis occurs only during one specific stage in the Cell Cycle. Then replicated chromosomes (DNA) are distributed to daughter nuclei by a complex series of events during cell division. These events are themselves under genetic control. This ebook is exclusively for this university only. Cannot be resold/distributed. Cell Cycle The Cell Cycle or cell division cycle is the series of events that take place in a eukaryotic cell leading to its replication. These events can be divided in two broad periods; interphase during which the cell grows, accumulating nutrients needed for mitosis and duplicating its DNA and the mitotic (M) phase, during which the cell splits itself into two distinct cells called daughter cells.

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  eBook - ePub

  Advanced Molecular Biology

  A Concise Reference

  • Richard Twyman(Author)
  • 2018(Publication Date)
  • Garland Science

    (Publisher)

  Chapter 2

  The Cell Cycle

  Fundamental concepts and definitions

  • The Cell Cycle is the sequence of events between successive cell divisions.
  • Many different processes must be coordinated during the Cell Cycle, some of which occur continuously (e.g. cell growth) and some discontinuously, as events or landmarks (e.g. cell division). Cell division must be coordinated with growth and DNA replication so that cell size and DNA content remain constant.
  • The Cell Cycle comprises a nuclear or chromosomal cycle (DNA replication and partition) and a cytoplasmic or cell division cycle (doubling and division of cytoplasmic components, which in eukaryotes includes the organelles). The DNA is considered separately from other cell contents because it is usually present in only one or two copies per vegetative cell, and its replication and segregation must therefore be precisely controlled. Most of the remainder of the cell contents are synthesized continuously and in sufficient quantity to be distributed equally into the daughter cells when the parental cell is big enough to divide. An exception is the centro-some, an organelle that is pivotal in the process of chromosome segregation itself, which is duplicated prior to mitosis and segregated into the daughter cells with the chromosomes (the centrosome cycle).
  • In eukaryotes, the two major events of the chromosomal cycle, replication and mitosis, are controlled so that they can never occur simultaneously. Conversely, in bacteria the analogous processes, replication and partition, are coordinated so that partially replicated chromosomes can segregate during rapid growth. The eukaryotic Cell Cycle is divided into discrete phases which proceed in a particular order, whereas the stages of the bacterial Cell Cycle may overlap.

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  eBook - PDF

  Development Biology

  • Edward Bittar(Author)
  • 1998(Publication Date)
  • Elsevier Science

    (Publisher)

  Chapter I Control of The Cell Cycle J. RICHARD DICKINSON and DAVID LLOYD Introduction 1 Methodology 3 Cell Cycle Control Points: Genetics of the Cell Cycle 4 Timer Controls 6 Implications of Cell Cycle Research 8 Future Research 10 Notes 11 INTRODUCTION The cell division cycle is the most fundamental of all developmental processes. Its outcome includes the proper replication and segregation of the genetic material during the formation of genetically identical daughter cells (Figure 1). The dou- bling in cell mass, and on average, of each type of cellular constituent, membrane component, and organelle, also relies on the efficient completion of this set of events (Nasmyth, 1996). The distinct stages of the overall process still bear the designations G 1, S, G 2, and M based on early cytological observations: S (for synthesis) is the phase of DNA replication; M is mitosis, in which segregation of cellular constituents precedes cell Principles of Medical Biology, Volume II Developmental Biology, pages 1-12. Copyright 9 1998 by JAI Press Inc. All rights of reproduction in any form reserved. ISBN: 1-55938-816-I 2 I. RICHARD DICKINSON and DAVID LLOYD ~,l~osis) t ion) Figure 1. The eukaryotic cell division cycle. division G 1 and G 2 are the gaps between these two microscopically-observable stages. As well as identification of the biochemical steps of this complex dynamic pro- cess, both spatial and temporal controls need to be understood (Mackinnon and Gilbert, 1992; Lloyd and Gilbert, 1998). Only then will it become possible to fathom the sources and early consequences of derangement to normal cellular growth and divi- sion. We may ask why it is that in cultures of simple unicellular organisms cell division depends on the presence of every necessary nutrient; what of the more complex ques- tion of why, under similar nutrient status, stem cells (for epidermis or of bone marrow) continue to divide, whereas neurons do not.

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  Biology 2e

  • Mary Ann Clark, Jung Choi, Matthew Douglas(Authors)
  • 2018(Publication Date)
  • Openstax

    (Publisher)

  The Cell Cycle has two major phases: interphase and the mitotic phase (Figure 10.5). During interphase, the cell grows and DNA is replicated. During the mitotic phase, the replicated DNA and cytoplasmic contents are separated, and the cell cytoplasm is typically partitioned by a third process of the Cell Cycle called cytokinesis. We should note, however, that interphase and mitosis (kayrokinesis) may take place without cytokinesis, in which case cells with multiple nuclei (multinucleate cells) are produced. Figure 10.5 The Cell Cycle in multicellular organisms consists of interphase and the mitotic phase. During interphase, the cell grows and the nuclear DNA is duplicated. Interphase is followed by the mitotic phase. During the mitotic phase, the duplicated chromosomes are segregated and distributed into daughter nuclei. Following mitosis, the cytoplasm is usually divided as well by cytokinesis, resulting in two genetically identical daughter cells. Interphase During interphase, the cell undergoes normal growth processes while also preparing for cell division. In order for a cell to move from interphase into the mitotic phase, many internal and external conditions must be met. The three stages of interphase are called G 1 , S, and G 2 . G 1 Phase (First Gap) The first stage of interphase is called the G 1 phase (first gap) because, from a microscopic point of view, little Chapter 10 | Cell Reproduction 283 change is visible. However, during the G 1 stage, the cell is quite active at the biochemical level. The cell is accumulating the building blocks of chromosomal DNA and the associated proteins as well as accumulating sufficient energy reserves to complete the task of replicating each chromosome in the nucleus. S Phase (Synthesis of DNA) Throughout interphase, nuclear DNA remains in a semi-condensed chromatin configuration.

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  Infrastructure and Activities of Cells

  Biotechnology by Open Learning

  • M.C.E. van Dam-Mieras, B C Currell, R C E Dam-Mieras(Authors)
  • 2016(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  1) During cell division the duplication of most of the cell's constituents need not be controlled exactly. 2) Cell Cycle times vary from one cell type to another, with most of the variation occurring in Gi. 3) The M-phase of the Cell Cycle in rapidly growing cells can begin before the end of the S-phase. 8.4.3 The causal connections between the four phases of the Cell Cycle It is now clear that the interphase is a period during which elaborate preparations are being made to allow the cell to divide and that these preparations occur in a precisely ordered sequence of events. The material in this next section covers some of the ways that the sequence of events can be investigated and discusses how the phases of the Cell Cycle are causally related. It is difficult to analyse the events underlying the Cell Cycle in the complex tissues of an intact animal. Fortunately, certain cell types can be grown in isolation in a complex, semi-defined medium. The analysis of the events of the Cell Cycle has been simplified by the use of large populations of tissue culture cells which are in the same phase of the Cell Cycle. It is possible to obtain such synchronised cells in a number of ways. For example, the first attempts to prepare synchronous cultures involved the use of chemicals that were known to arrest cells at a particular stage of the Cell Cycle. Treatment of an asynchronous population of tissue culture cells will eventually cause all the cells to become arrested at the same stage. Upon subsequent removal of the chemical block all the cells will resume cycling at the same point in the Cell Cycle. You may recall from Chapter 4, that colchicine causes disaggregation of the microtubules of the cytoskeleton. These microtubules are also involved in the process of mitosis. Treatment of cells with this chemical therefore prevents cells carrying out mitosis.

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  DNA Replication

  Current Advances

  • Herve Seligmann(Author)
  • 2011(Publication Date)
  • IntechOpen

    (Publisher)

  Part 4 The Cell Cycle and Replication 17 Cell Cycle Regulation of DNA Replication in S. cerevisiae Jorrit M. Enserink Centre for Molecular Biology and Neuroscience (CMBN) Oslo University Hospital, Oslo Norway 1. Introduction Cell duplication is a strictly regulated process that underlies growth and development of all organisms. The ordered series of events that lead to the duplication of a cell is commonly referred to as the Cell Cycle. The purpose of the Cell Cycle is to transmit an intact and complete copy of the genome from one generation to the next. Although certain highly specialized cell types undergo multiple rounds of replication per Cell Cycle in a developmentally coordinated process termed endoreplication, like for example megakaryocytes, plant endosperm, Drosophila follicle and nurse cells, and rodent trophoblasts (Lee, Davidson et al. 2009), the vast majority of cells in an organism replicate their DNA only once per Cell Cycle. Endoreplication differs from the aberrant process of re-replication in that it is highly regulated, and DNA content increases by clearly delineated genome doublings, whereas re-replication results from unscheduled activation of the DNA replication process (Lee, Davidson et al. 2009). Re-replication can result in genome instability that can have adverse effects on the well-being of the organism. Multiple mechanisms have evolved that prevent re-replication by restricting DNA replication to one specific phase of the Cell Cycle. Several protein complexes required for the various steps of DNA replication are separated in time and space during the Cell Cycle, and are only active during brief phases of the Cell Cycle. In this chapter I will discuss regulation of DNA replication by the Cell Cycle.

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  Biology for AP® Courses

  • Julianne Zedalis, John Eggebrecht(Authors)
  • 2018(Publication Date)
  • Openstax

    (Publisher)

  Science Practice 1.2 The student can describe representations and models of natural or man-made phenomena and systems in the domain. Learning Objective 3.8 The student can describe the events that occur in the Cell Cycle. The length of the Cell Cycle is highly variable, even within the cells of a single organism. In humans, the frequency of cell turnover ranges from a few hours in early embryonic development, to an average of two to five days for epithelial cells, and to an entire human lifetime spent in G 0 by specialized cells, such as cortical neurons or cardiac muscle cells. There is also variation in the time that a cell spends in each phase of the Cell Cycle. When fast-dividing mammalian cells are grown in culture (outside the body under optimal growing conditions), the length of the cycle is about 24 hours. In rapidly dividing human cells with a 24-hour Cell Cycle, the G 1 phase lasts approximately nine hours, the S phase lasts 10 hours, the G 2 phase lasts about four and one-half hours, and the M phase lasts approximately one-half hour. In early embryos of fruit flies, the Cell Cycle is completed in about eight minutes. The timing of events in the Cell Cycle is controlled by mechanisms that are both internal and external to the cell. Regulation of the Cell Cycle by External Events Both the initiation and inhibition of cell division are triggered by events external to the cell when it is about to begin the replication process. An event may be as simple as the death of a nearby cell or as sweeping as the release of growth- promoting hormones, such as human growth hormone (HGH). A lack of HGH can inhibit cell division, resulting in dwarfism, whereas too much HGH can result in gigantism. Crowding of cells can also inhibit cell division. Another factor that can initiate cell division is the size of the cell; as a cell grows, it becomes inefficient due to its decreasing surface-to- volume ratio.

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  eBook - ePub

  Cellular Signal Processing

  An Introduction to the Molecular Mechanisms of Signal Transduction

  • Friedrich Marks, Ursula Klingmüller, Karin Müller-Decker(Authors)
  • 2017(Publication Date)
  • Garland Science

    (Publisher)

  Regulation of Cell Division 12

  Cell proliferation is mandatory for reproduction and for development, repair, and maintenance of tissues. In fact, the apparatus of cell division is an ultimate target of most of the signal-processing reactions explained in the previous chapters. In the following, we shall have a closer look at pathways that connect this apparatus with the cell’s signal-processing network. The investigation of these interactions has tremendous practical consequences because defective transduction of signals controlling cell proliferation is a major cause of cancer.

  12.1 The Cell Cycle

  Proliferating cells pass through a sequence of phases presented as a cyclic process. This Cell Cycle is conserved in all eukaryotes. It provides a perfect example of how a highly complex cellular event is controlled temporally and spatially by signaling reactions that are tightly interlinked and feedback-controlled to ensure that the genetic material has been correctly copied and evenly distributed to the daughter cells. Pioneering work on Cell Cycle regulation was honored by the Nobel Prize in Physiology or Medicine for 2001, awarded to Leland H. Hartwell, R. Timothy Hunt, and Paul M. Nurse.

  The production of intact and genetically identical daughter cells presupposes a precise sequence of the cycle phases. For instance, separation of chromosomes must not occur before complete chromosome condensation, which requires DNA replication to be finished to proceed correctly. Therefore, the Cell Cycle is interrupted at least three times by checkpoints (Figure 12.1 ) that give the data-processing network an opportunity to monitor the precision of DNA replication and chromosome segregation and, if necessary, to launch repair measures or, in the case of irreparable damage, to promote cell death (for details see Section 12.8

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  eBook - PDF

  Karp's Cell Biology

  • Gerald Karp, Janet Iwasa, Wallace Marshall(Authors)
  • 2018(Publication Date)
  • Wiley

    (Publisher)

  The beauty and precision of cell division is best appreciated by watching a time‐lapse video of the process (e.g., www.bio.unc.edu/faculty/salmon/lab/mitosis/mitosismovies. html) rather than reading about it in a textbook. Mitosis is a process of nuclear division in which the repli- cated DNA molecules of each chromosome are faithfully segre- gated into two nuclei. Mitosis is usually accompanied by cytokinesis, a process by which a dividing cell splits in two, parti- tioning the cytoplasm into two cellular packages. The two daugh- ter cells resulting from mitosis and cytokinesis possess a genetic content identical to each other and to the mother cell from which they arose. Mitosis, therefore, maintains the chromosome num- ber and generates new cells for the growth and maintenance of an organism. Mitosis can take place in either haploid or diploid cells. Haploid mitotic cells are found in fungi, plant gameto- phytes, and a few animals (including male bees known as drones). Mitosis is a stage of the Cell Cycle when the cell devotes virtually all of its energy to a single activity—chromosome segregation. As a result, most metabolic activities of the cell, including transcrip- tion and translation, are curtailed during mitosis, and the cell becomes relatively unresponsive to external stimuli. We have seen in previous chapters how much can be learned about the factors responsible for a particular process by studying that process outside of a living cell (page 469). Our understanding of the biochemistry of mitosis has been greatly aided by the use of extracts prepared from frog eggs. These extracts contain stockpiles of all the materials (histones, tubu- lin, etc.) necessary to support mitosis. When chromatin or whole nuclei are added to the egg extract, the chromatin is compacted into mitotic chromosomes, which are segregated by a mitotic spindle that assembles spontaneously within the cell‐ free mixture.

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  Cells and Tissues in Culture

  Methods, Biology and Physiology

  • E. N. Willmer(Author)
  • 2015(Publication Date)
  • Academic Press

    (Publisher)

  CHAPTER 6 Cell Division H. F I R K E T Laboratoire d'Anatomie pathologique 3 Universite de Liege, Belgium I. Introduction 203 II. Mitosis 4 A. General survey 204 B. Special aspects 206 III. The Cell Cycle 218 A. Duration of the cycle 218 B. Morphological changes 220 C. Metabolic changes (DNA cycle) 220 D. General considerations 225 E. Effect of ionizing radiations on the Cell Cycle 226 IV. Mitogenesis 227 V. Synchronism of Divisions in Cultures 229 VI. Conclusions 230 References 231 I. I N T R O D U C T I O N Ever since tissues were first cultivated in vitro, cultures have constituted one of the best biological objects for the study of cell division. They combine various favourable conditions to an unusual extent: flattening out of the cells enlarges the images of division as compared to more compact tissues in the animal; observation on the living cells, which is necessary to understand the variations—experimental or otherwise —of an essentially dynamic phenomenon, is particularly easy; cell multiplication can occur at a high rate and in reproducible conditions; cells used are similar to or even identical with those found in the mammalian body. To these advantages is added the immense array of experimental interventions made possible by in vitro cultivation. To understand cell division is a challenge of such magnitude that all possible materials have been analysed with this aim in view. Almost every year, symposia or general reviews are devoted to some special aspect of cell division (e.g., in recent years, Anderson, 1956; Stern, 1956; Mazia, 1956; Swann, 1957, 1958; Gross, 1960; Levine, 1961). These 204 H. FIRKET reviews are often longer than the present chapter could reasonably be, so the latter is bound to be very incomplete. Most of the older literature was reviewed in Hughes' book The Mitotic Cycle (1952) and the very large and recent treatise by Mazia (1961) covers an immense and varied ground.

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