Cell Cycle

6 Key excerpts on "Cell Cycle"

• 

  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.

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Upstream Industrial Biotechnology, 2 Volume Set

  • Michael C. Flickinger(Author)
  • 2013(Publication Date)
  • Wiley

    (Publisher)

  Chapter 5: Cell Cycle in Bioprocesses Mariam Naciri and Mohamed Al-rubeai University College Dublin, Belfield, Dublin, Ireland The Cell Cycle is the name given to the process by which a cell matures, synthesizes DNA, and divides to form daughter cells. Thus the Cell Cycle is a fundamental process with analogous mechanisms found in all cells, from the most primitive bacterium to higher animals and plants, from the unicellular to the most complex multicellular organism. It is regulated by several ordered and directional molecular events and controlled by an elaborate system that if altered could result in physiological damage and cell death (1). Here we describe the mammalian Cell Cycle, highlight its importance in biotechnology, and describe some Cell Cycle applications in animal cell biotechnology. mammalian Cell Cycle; cell division; mitosis; flow cytometry; product expression 5.1 Introduction The Cell Cycle model (G 1 -event model) currently accepted by authors of the major cell and molecular biology books (2–5) describes the Cell Cycle as discrete phases controlled by Cell Cycle proteins interacting with each other and directing cellular events including DNA synthesis and cell division. However, the validity of this model and the interpretation of many experiments that underpin the current established view of the Cell Cycle and its regulation have been questioned (6, 7). The proposed alternative, the continuum model, suggests that the Cell Cycle does not exist as currently recognized but takes the form of a continuum from one cell division to the next, rather than discrete phases with discrete groups of regulatory proteins. A hypothetical initiator of DNA replication is synthesized by the cell during all phases of the Cell Cycle, and its concentration reaches a critical level that initiates DNA synthesis. Thus the cell can control its rate of division by regulating the amount of initiator

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Cell Biology E-Book

  • Thomas D. Pollard, William C. Earnshaw, Jennifer Lippincott-Schwartz, Graham Johnson(Authors)
  • 2016(Publication Date)
  • Elsevier

    (Publisher)

  chromosome cycle (the replication and partitioning of the genome into two daughter cells). The chromosome cycle is driven by a sequence of enzymatic cascades that produce a sequence of discrete biochemical “states” of the cytoplasm. Progress through the Cell Cycle is ratchet-like and irreversible because each new state arises not only by expression or activation of a new cohort of activities, but also by destruction or inactivation of key activities characteristic of the preceding state. Later sections of this chapter explain these mechanisms.

  FIGURE 40.2 INTRODUCTION TO THE CELL-CYCLE PHASES.

  A, Diagrams of cellular morphology and chromosome structure across the Cell Cycle. B, Length of cell-cycle phases in cultured cells. C, Time scale of cell-cycle phases.

  Phases of the Cell Cycle

  In describing the Cell Cycle, it is convenient to divide the process into several phases. Recognition of these phases began in 1882, when Flemming named the process of nuclear division mitosis (from the Greek mito, or “thread”) after he first observed the condensed chromosomes. Mitosis was a clear Cell Cycle landmark, and the rest of the Cell Cycle between mitoses was called interphase (Box 40.1 ).

  Box 40.1 Selected Key Terms

  M phase: Cell division, comprising mitosis, when a fully grown cell segregates the replicated chromosomes to opposite ends of a molecular scaffold, termed the spindle, and cytokinesis, when the cell cleaves between the separated chromosomes to produce two daughter cells. In general, each daughter cell receives a complement of genetic material and organelles identical to that of the parent cell.

  Interphase: The portion of the Cell Cycle when cells grow and replicate their DNA. Interphase has three sections. The G 1 (first gap) phase is the interval between mitosis and the onset of DNA replication. The S (synthetic) phase is the time when DNA is replicated. The G 2 (second gap) phase is the interval between the termination of DNA replication and the onset of mitosis. In multicellular organisms, many differentiated cells no longer actively divide. These nondividing cells (which may physiologically be extremely active) are in the G 0 phase, a branch of the G1

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  The Molecular Biology of Cancer

  A Bridge from Bench to Bedside

  • Stella Pelengaris, Michael Khan(Authors)
  • 2013(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  1 at which the cell commits to DNA synthesis (S phase); and at the beginning of M phase when the cell commits to chromosome condensation and mitosis. Seminal studies have shown that key protein complexes are formed at each of the two committal points, comprising a cyclin, and a protein kinase called p34. The existence of such a complex was described biochemically when a factor called maturation promoting factor (MPF) was isolated that could initiate mitosis in certain mutant yeast strains whose Cell Cycle was arrested at this stage. It was the coupling of this type of biochemical research with genetics that defined and elucidated many of the steps in the cycle.

  The Cell Cycle is divided into four distinct and microscopically recognizable phases (Fig. 4.1 ): the replication of chromosomal DNA during the synthesis phase (S phase), the partitioning of replicated chromosomes during mitosis (M phase), and two gaps, one before and one after S phase, that are referred to as G1 and G2 , respectively. Broadly, M phase in the Cell Cycle includes the various microscopically observed stages of nuclear division and cytokinesis (mitosis) and is itself divided into phases termed prophase, prometaphase, metaphase, anaphase, and telophase (Fig. 4.2 ). Interphase is the term that encompasses stages G1 , S, and G2 of the Cell Cycle.

  The duration of the Cell Cycle can vary remarkably between cell types. For example, cells in early embryos can proceed through continuous cycles with each Cell Cycle completed in a mere half hour. This is in contrast with cells of the adult, where a fairly rapidly dividing mammalian cell would have a cycle time of 12–24 hours, whereas the Cell Cycle of a human liver cell can last longer than a year! The much longer duration of cell-cycle transit observed in adult tissues, in contrast to early embryonic cells, is due to the gap phases, G1 and G2

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Molecular Cell Biology of the Growth and Differentiation of Plant Cells

  • Ray J. Rose(Author)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  Study of the Cell Cycle began in the second half of the XIXth century with the discovery of cell division and the understanding that cells originate from pre-existing cells. With the identification of chromosomes as the source of genetic information at the beginning of the XXth century, the Cell Cycle was placed at the centre of the growth, development and heredity for all living organisms (Nurse 2000). Next, in the 1950s the elucidation of the structure of the DNA molecule, and the use of radioactive labelling led to the finding that in eukaryotes, DNA is duplicated during a restricted phase of the Cell Cycle in interphase that was called S-phase (for synthesis). The Cell Cycle was thus divided in four phases, S-phase, M-phase or mitosis and two so-called Gap phases, G1 before S-phase and G2 before mitosis. After these crucial conceptual advances, further dissection of the Cell Cycle and notably of its regulation had to wait until technical progresses allowed its genetic analysis. This was achieved in the 1970s: combination of genetics, biochemistry and molecular biology allowed the identification of Cyclin Dependent Kinase (CDK)-cyclin complexes as the universal motors of Cell Cycle regulation in all eukaryotes. CDKs are protein kinases that phosphorylate various substrates to promote transitions from one Cell Cycle phase to the next. Their activity is modulated by their association with the regulatory sub-units called cyclins that are characterized by their cyclic accumulation during the Cell Cycle. In 2001, L. Hartwell, P. Nurse and T. Hunt were awarded the Nobel prize in Physiology or Medicine for their complementary achievements: their work not only unravelled the role of CDK/cyclin complexes but also introduced the concept of checkpoints to explain the observation that impairing one phase of the Cell Cycle inhibits subsequent progression.

  Basic mechanisms regulating Cell Cycle progression, DNA replication and mitosis are conserved in all eukaryotes including plants. This high degree of conservation allowed fast progress in the understanding of Cell Cycle regulation in all organisms. For example, the first plant CDK was isolated by functional complementation of a yeast mutant with an Alfalfa cDNA (Hirt et al. 1991), and considerable progress has been made in the last 35 years in our understanding of plant Cell Cycle transitions. In spite of this conservation of molecular effectors, the plant Cell Cycle has a number of specificities. One obvious difference concerns plant mitosis that is characterized by the absence of centrosomes and mechanisms governing cytokinesis. Another hallmark of the plant Cell Cycle is the relatively frequent occurrence of endoreduplication, a particular type of Cell Cycle consisting of several rounds of DNA replication without mitosis, and leading to an increase in cell ploidy. Although this process can be found in animals, it is generally restricted to relatively specific cell types such as the salivary glands in Drosophila and hepatocytes in mammals (Fox and Duronio 2013). By contrast in plants, it is widely distributed in various organs such as fruits in tomato, endosperm in cereals or even leaves in plants such as Arabidopsis (Fox and Duronio 2013). In addition, there are also differences in terms of molecular mechanisms regulating Cell Cycle transitions between plants and other eukaryotes. In the present chapter, we will describe plant Cell Cycle regulation with a specific emphasis on the molecular mechanisms that control Cell Cycle transitions, and we will briefly discuss how these basic mechanisms are modulated during plant development or according to external stimuli.

  Sign up to read

  Learn more about book
• 

  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

  Sign up to read

  Learn more about book