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Author: Dongyang Li
Publisher:
ISBN:
Category :
Languages : en
Pages : 178
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Book Description
The defining feature of living organisms is their capacity to reproduce and pass on the genetic information so that their progeny can flourish. For bacteria, reproduction is a feat by itself--Escherichia coli cells cultured in optimal conditions grow rapidly and divide about every 20 minutes. In other words, the cell has to replicate all cellular contents, and be ready to divide evenly into two daughter cells within this 20 minutes. Biosynthesis of new cellular materials, e.g. proteins, nucleic acis, lipids and other metabolites accumulate and roughly doubles after every generation. Notably, the deoxyribonucleic acid (DNA) encodes genetic informationand needs to be duplicated in order to faithfully pass on this information to the progeny. This process of DNA replication in the cell needs to dynamically adapt to fluctuation in growth condition and cellular physiology. Such coordination is controlled at the first step of replcation--the initiation of replication. In this thesis, I presented the development of methods for measuring DNA replication duration (replication period), the quantitative relationship between DNA replication and cell size as well as the mechanism of replication initiation. DNA replication measurement laid the foundation of studying the quantitative relationship between cell size and DNA replication. A general growth law was proposed to describe cell size regulation in light of three physiological variables including biosynthesis rate, cell cycle progression and replicaiton initiation. Of the three variables, the mass when cell initiates replication (initiation mass) remains invariant despite a wide spectrum of antibiotics or growth limitation challenge. This invariant initiation mass called into question about the mechanism of initiation to achieve such constancy. We proposed a simple threshold model to explain how cells can maintain a invariant initiation mass by regulating the expression of initiation regulators (initiators). The initiation mass is inversely proportional to the initiator levels, which is held constant. Experimental evidence was provided to test our model prediction.
Author: Dongyang Li
Publisher:
ISBN:
Category :
Languages : en
Pages : 178
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Book Description
The defining feature of living organisms is their capacity to reproduce and pass on the genetic information so that their progeny can flourish. For bacteria, reproduction is a feat by itself--Escherichia coli cells cultured in optimal conditions grow rapidly and divide about every 20 minutes. In other words, the cell has to replicate all cellular contents, and be ready to divide evenly into two daughter cells within this 20 minutes. Biosynthesis of new cellular materials, e.g. proteins, nucleic acis, lipids and other metabolites accumulate and roughly doubles after every generation. Notably, the deoxyribonucleic acid (DNA) encodes genetic informationand needs to be duplicated in order to faithfully pass on this information to the progeny. This process of DNA replication in the cell needs to dynamically adapt to fluctuation in growth condition and cellular physiology. Such coordination is controlled at the first step of replcation--the initiation of replication. In this thesis, I presented the development of methods for measuring DNA replication duration (replication period), the quantitative relationship between DNA replication and cell size as well as the mechanism of replication initiation. DNA replication measurement laid the foundation of studying the quantitative relationship between cell size and DNA replication. A general growth law was proposed to describe cell size regulation in light of three physiological variables including biosynthesis rate, cell cycle progression and replicaiton initiation. Of the three variables, the mass when cell initiates replication (initiation mass) remains invariant despite a wide spectrum of antibiotics or growth limitation challenge. This invariant initiation mass called into question about the mechanism of initiation to achieve such constancy. We proposed a simple threshold model to explain how cells can maintain a invariant initiation mass by regulating the expression of initiation regulators (initiators). The initiation mass is inversely proportional to the initiator levels, which is held constant. Experimental evidence was provided to test our model prediction.
Author: Norbert Seabrook Hill
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 228
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Book Description
DNA replication, nucleoid segregation, and cell division must be coordinated with growth and cell size to ensure viability in all organisms. Failure to do so yields progeny with an inappropriate fraction of genetic and cytosolic material, reducing the fitness of the organism. This dissertation has sought to understand the role of cell size in two fundamental aspects of bacterial physiology: 1) How do bacteria regulate cell size in response to nutrient availability? 2) Does cell size govern progression of the cell cycle? Growth rate and nutrient availability are primary determinants of cell size in single-celled organisms. Bacterial cells cultured in nutrient-rich circumstances are twice the size of cells grown in nutrient-poor conditions. How bacteria are able to perceive nutrient levels and amend cell size is largely undefined. In Chapter 2, I report the identification and characterization of the glucosyltransferase OpgH as a uridine diphosphate (UDP) glucose-dependent effector that coordinates Escherichia coli cell size with growth rate and nutritional status. High intracellular levels of UDP-glucose accumulate during growth in nutrient-rich conditions. In turn, UDP-glucose activates OpgH to sequester the essential division protein FtsZ, which obstructs assembly and/or maturation of the cytokinetic ring, delaying division to increase cell size. In this way, OpgH directly gauges nutrient status and modifies cell size through the timing of division. Cell cycle progression is regulated by cell size in all organisms. In bacteria, it has long been postulated that the achievement of a particular cell size triggers chromosomal replication. Chapter 3 of this dissertation describes a comparative study between E. coli and Bacillus subtilis examining whether cell mass determines the timing of initiation of DNA replication. Using mutants defective for cell size, my data confirms that E. coli directly ties the initiation event to cell mass. However, counter to the paradigm, the phenomenon of initiation mass is not conserved to B. subtilis, which appears to coordinate DNA replication through a cell cycle timer device. This dissertation yields several original conclusions. First, the discovery of OpgH as a UDP-glucose-activated antagonist of FtsZ polymerization is a significant advance in the understanding of cell size control in bacteria. However, these results in tandem with the cognate pathway in B. subtilis reveal a remarkable instance of convergent evolution. Based on this, I propose that UDP-glucose and cognate UDP-glucose binding proteins are a widely conserved strategy to direct nutrient-dependent changes in cell size. In addition, the revelation that initiation of DNA replication is cell size-independent in B. subtilis adds to a growing sentiment that mechanisms controlling DNA replication are fundamentally divergent throughout bacteria.
Author: National Research Council
Publisher: National Academies Press
ISBN: 0309066344
Category : Science
Languages : en
Pages : 171
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Book Description
How small can a free-living organism be? On the surface, this question is straightforward-in principle, the smallest cells can be identified and measured. But understanding what factors determine this lower limit, and addressing the host of other questions that follow on from this knowledge, require a fundamental understanding of the chemistry and ecology of cellular life. The recent report of evidence for life in a martian meteorite and the prospect of searching for biological signatures in intelligently chosen samples from Mars and elsewhere bring a new immediacy to such questions. How do we recognize the morphological or chemical remnants of life in rocks deposited 4 billion years ago on another planet? Are the empirical limits on cell size identified by observation on Earth applicable to life wherever it may occur, or is minimum size a function of the particular chemistry of an individual planetary surface? These questions formed the focus of a workshop on the size limits of very small organisms, organized by the Steering .Group for the Workshop on Size Limits of Very Small Microorganisms and held on October 22 and 23, 1998. Eighteen invited panelists, representing fields ranging from cell biology and molecular genetics to paleontology and mineralogy, joined with an almost equal number of other participants in a wide-ranging exploration of minimum cell size and the challenge of interpreting micro- and nano-scale features of sedimentary rocks found on Earth or elsewhere in the solar system. This document contains the proceedings of that workshop. It includes position papers presented by the individual panelists, arranged by panel, along with a summary, for each of the four sessions, of extensive roundtable discussions that involved the panelists as well as other workshop participants.
Author: Monika Glinkowska
Publisher: Springer
ISBN: 3319105337
Category : Science
Languages : en
Pages : 56
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Book Description
This work describes the current knowledge of biochemical mechanisms regulating initiation of DNA replication in Escherichia coli, which focuses on the control of activity of the DnaA protein. Examples of direct linkages between DNA replication and other cellular processes are provided. In addition, similarities of the mechanisms of regulation of DNA replication operating in prokaryotic and eukaryotic cells are identified, and implications for understanding more complex processes, like carcinogenesis are suggested. Studies of recent years provided evidence that regulation of DNA replication in bacteria is more complex than previously anticipated. Multiple layers of control seem to ensure coordination of this process with the increase of cellular mass and the division cycle. Metabolic processes and membrane composition may serve as points where integration of genome replication with growth conditions occurs. It is also likely that coupling of DNA synthesis with cellular metabolism may involve interactions of replication proteins with other macromolecular complexes, responsible for various cellular processes. Thus, the exact set of factors participating in triggering the replication initiation may differ depending on growth conditions. Therefore, understanding the regulation of DNA duplication requires placing this process in the context of the current knowledge on bacterial metabolism, as well as cellular and chromosomal structure. Moreover, in both Escherichia coli and eukaryotic cells, replication initiator proteins were shown to play other roles in addition to driving the assembly of replication complexes, which constitutes another, yet not sufficiently understood, layer of coordinating DNA replication with the cell cycle.
Author: Ole Maaløe
Publisher:
ISBN:
Category : Bacteria
Languages : en
Pages : 306
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Author:
Publisher:
ISBN: 9780815332183
Category : Cells
Languages : en
Pages : 0
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Author: Anne Eliane Chiaramello
Publisher:
ISBN:
Category : DNA
Languages : en
Pages : 300
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Book Description
The initiation of DNA synthesis at the chromosomal replication origin, oriC, in Escherichia coli involves an RNA polymerase-mediated step. The level of synthesis of transcripts moving counterclockwise toward oriC is controlled at two promoters, P1 (asnC) and P2 (mioC), and at two transcription terminator regions, T1 and T2. As shown by S1 mapping, termination at the T2 region occurs to the right of oriC at nucleotides 297-299 and 306-310, while major termination events in the T1 region occur in and near the mioC promoter. The majority of transcripts entering oriC originates from the mioC promoter. Transcription from the mioC promoter has been shown to enhance the frequency of initiation of DNA replication of oriC containing plasmids, and to stabilize these plasmids in the host cells. The mioC promoter, which is stringently controlled, is also growth rate regulated. The amount of mioC transcripts relative to the amount of total RNA was inversely correlated with growth rate. This transcript is characterized by a short half-life (1.5 min). The mioC promoter, which contains a DnaA protein binding site, was much less susceptible to repression by DnaA protein when located in the chromosome, than when located in a plasmid. Only a very high concentration of DnaA protein repressed the mioC promoter. The DnaA protein, which is required for initiation of DNA replication from oriC, is growth rate regulated. As shown by RNase protection, this regulation is exerted at the transcriptional level, affecting both promoters, dnaAp1 and dnaAp2. Transcription from these two promoters is also stringently controlled. The amount of DnaA protein in spoT mutants, which are deficient in ppGpp pyrophosphorylase activity, decreases as the severity in the mutation increases. Thus, the intracellular concentration of ppGpp influences the expression of the dnaA gene. In conclusion, the growth rate regulation and stringent control of the dnaA gene suggest that one way in which DNA replication is coordinated with the growth rate is via ppGpp synthesis at the ribosome.
Author: J. M. Mitchison
Publisher: CUP Archive
ISBN: 9780521082518
Category : Science
Languages : en
Pages : 324
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Author: Andrei Kuzminov
Publisher: Landes Bioscience
ISBN:
Category : Medical
Languages : en
Pages : 234
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Author: Jan Löwe
Publisher: Springer
ISBN: 331953047X
Category : Science
Languages : en
Pages : 457
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Book Description
This book describes the structures and functions of active protein filaments, found in bacteria and archaea, and now known to perform crucial roles in cell division and intra-cellular motility, as well as being essential for controlling cell shape and growth. These roles are possible because the cytoskeletal and cytomotive filaments provide long range order from small subunits. Studies of these filaments are therefore of central importance to understanding prokaryotic cell biology. The wide variation in subunit and polymer structure and its relationship with the range of functions also provide important insights into cell evolution, including the emergence of eukaryotic cells. Individual chapters, written by leading researchers, review the great advances made in the past 20-25 years, and still ongoing, to discover the architectures, dynamics and roles of filaments found in relevant model organisms. Others describe one of the families of dynamic filaments found in many species. The most common types of filament are deeply related to eukaryotic cytoskeletal proteins, notably actin and tubulin that polymerise and depolymerise under the control of nucleotide hydrolysis. Related systems are found to perform a variety of roles, depending on the organisms. Surprisingly, prokaryotes all lack the molecular motors associated with eukaryotic F-actin and microtubules. Archaea, but not bacteria, also have active filaments related to the eukaryotic ESCRT system. Non-dynamic fibres, including intermediate filament-like structures, are known to occur in some bacteria.. Details of known filament structures are discussed and related to what has been established about their molecular mechanisms, including current controversies. The final chapter covers the use of some of these dynamic filaments in Systems Biology research. The level of information in all chapters is suitable both for active researchers and for advanced students in courses involving bacterial or archaeal physiology, molecular microbiology, structural cell biology, molecular motility or evolution. Chapter 3 of this book is open access under a CC BY 4.0 license.
