Cell Growth

6 Key excerpts on "Cell Growth"

• 

  eBook - ePub

  The Molecular Basis of Cancer E-Book

  The Molecular Basis of Cancer E-Book

  • John Mendelsohn, Peter M. Howley, Mark A. Israel, Joe W. Gray, Craig B. Thompson(Authors)
  • 2014(Publication Date)
  • Saunders

    (Publisher)

  12 Cell Growth David A. Guertin and David M. Sabatini What Is Cell Growth? Cell Growth is the process by which cells accumulate mass and increase in physical size. On average, dividing animal cells are approximately 10 to 20 μm in diameter. Terminally differentiated cells have a wide range of sizes, spanning from tiny red blood cells (∼5 μm in diameter) to motor neurons, which can grow to hundreds of micrometers in length. 1 For a typical dividing cell, water accounts for about 70% of the weight of a cell, and macromolecules, such as nucleic acids, proteins, polysaccharides, and lipids constitute most of the remaining mass (∼25%—trace amounts of ions and small molecules make up the difference). The largest contribution to cellular dry mass is typically from proteins, which makes up about 18% of the total cell weight on average. There are many physical, chemical, and biological factors that affect the biosynthesis of macromolecules and therefore final cell size. Intracellular signaling networks that regulate metabolism and control macromolecule biosynthesis are particularly relevant to cancer. As discussed later, deregulation of the cellular circuitry controlling biomass accumulation is associated with a wide spectrum of human cancers. There are many different examples in nature of how cells can grow. In some cases, cell size is proportional to DNA content. For instance, continued DNA replication in the absence of cell division (called endoreplication) results in increased cell size. Megakaryoblasts, which mature into granular megakaryocytes, the platelet-producing cells of bone marrow, typically grow this way. These cells cease division and then undergo multiple rounds of DNA synthesis, increasing from about 20 μm to approximately 100 μm in diameter as a result of the increased DNA content. It is unclear whether increased DNA content simply leads to an increase in total cellular material or whether cells actively grow to cope with the larger genome size

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Two from One

  A Short Introduction to Cell Division Mechanisms

  • Michael Polymenis(Author)
  • 2022(Publication Date)
  • Wiley

    (Publisher)

  2 Cell Growth and Division

  • How do we measure Cell Growth?
  • What is the relationship between Cell Growth and division?
  • When and how do cells grow in the cell cycle?

  2.1 Balanced Growth and Cell Proliferation

  As the unit of life, the cell must carry out all the processes associated with life. Cells are open thermodynamic systems, exchanging both matter and energy with their environment. The entire enterprise of synthesizing a cell encompasses many more processes than those needed to duplicate and segregate the genome. Furthermore, the rate at which cells can divide usually depends not on how fast they can replicate their genome but on how fast they can synthesize everything else that goes into a newborn cell. If “The dream of every cell is to become two cells (Francois Jacob),” it is Cell Growth that makes those dreams come true.

  Imagine an environment where cells have constant nutrients and growth factors, and toxic products do not accumulate. When the number of cells is measured over successive cell cycles in such an environment, Cell Growth and division appear balanced. General cellular properties (e.g., cell size and composition) and cell proliferation rate remain constant. In these situations, cell proliferation behaves like a first‐order autocatalytic reaction. The change in the number of cells (N) over time (t) can be described with a simple equation: dN/dt = kN. The proportionality constant, k, is the specific proliferation rate constant. It solely reflects cells’ intrinsic properties and their ability to grow and divide in that particular environment. The apparent balance of growth and division means that the time it takes to double the number of cells is the same as the amount of time it takes to duplicate every cell component, from chromosomes to individual protein and RNA molecules. A plot of the logarithm of the number of cells over time will be a straight line, with a slope equal to k (Figure 2.1

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  The Physiology of Flowering Plants

  • Helgi Öpik, Stephen A. Rolfe(Authors)
  • 2005(Publication Date)
  • Cambridge University Press

    (Publisher)

  Part II Growth and development Chapter 6 Growth as a quantitative process 6.1 Introduction Growth is one of the most fundamental and conspicuous character-istics of living organisms, being the consequence of increase in the amount of living protoplasm. Externally this is manifested by the growing system getting bigger, and growth is therefore often defined as an irreversible increase in the mass, weight or volume of a living system. The size increase must be permanent; the swelling of a cell in water is not growth, being easily reversed by returning the cell to a solution of lower C . It is, however, possible to consider as growth developmental changes not immediately involving an increase in size. An amphibian embryo, or a Selaginella female gametophyte, for a long time utilizes the nutrient store with which it was released from the parent, to produce many new cells without any increase in over-all size, yet growing in the sense that living protoplasm is increasing at the expense of stored nutrients. Again, if dry mass is measured, a flowering plant seedling loses dry mass while utilizing reserves and growing. Growth is an exceedingly complex process. Every reaction asso-ciated with the synthesis and maintenance of living protoplasm is associated with it, which makes it complicated enough at the cellular level. At the organismal level, it means the coordinated multiplication, size increase and specialization of millions of cells, all arranged in precise positions. Growth processes are also syn-chronized with seasonal changes, plants responding to appropri-ate environmental stimuli to achieve this synchronization. This chapter is an introduction to growth and development of flower-ing plants, discussing the overall process, methods of measure-ment, elementary quantitative analysis of growth patterns, and growth rhythms.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Principles of Cell Proliferation

  • J. R. Heath(Author)
  • 2008(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  In some unicellular organisms (described further in Chapter 6) there is a strict relation-ship between the size of a cell and its position in the cell cycle. In multi-celled organisms, however, the relationship between cell size and cell cycle appears more complicated. Part of the problem is that it is difficult to rigorously define what is meant by cell size: is it the area occupied by a cell? its volume? or net mass? Using any of these criteria, it is evident that different cell types in the body have widely differing ‘masses’. In addition, cells within an otherwise uniform population appear to have differing sizes and shapes (look closely at Fig. 1.8). Experiments aimed at measuring the relationship between the volume of cells and their position in the cycle fail to give any strict correlation between the two parameters. This indicates that observable measures of cell size may indirectly reflect some underlying process such as the rate of protein synthesis. In this light it is clear that all cells, whatever their mass, will require an approximate dou-bling of protein content in the course of one cell cycle but the net amount of protein required may vary from cell to cell. This indicates that part of the mech-anism of progress through the cell cycle must involve a coupling of cell cycle events to general protein synthesis. The cell cycle therefore involves coupling progression to the translation of specific proteins (as manifest at the restriction point) as well as to general protein biosynthesis. Cell transformation and tumours So far we have been concerned with the behaviour of ‘normal’ cells derived from normal tissues. As is the case for much of biology, however, key insights have been obtained from the investigation of abnormal phenomena. In par-ticular, it had been recognised for many years that many of the regulatory cell cycle phenomena described above did not pertain in the case of cells derived from tumours.

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Basic Pathology

  An introduction to the mechanisms of disease

  • Sunil R. Lakhani, Caroline J. Finlayson, Susan A. Dilly, Mitesh Gandhi(Authors)
  • 2016(Publication Date)
  • CRC Press

    (Publisher)

  Pathological assessment of tissues has remained the lynchpin of diagnostic practice for over 100 years. It has become the core science of clinical medical practice, providing data for clinical management and a framework for future correlation of new markers and new therapies. With the current explosion of technology and data, it is important for pathologists and other clinical specialists to embrace and incorporate these changes into their training and practice. Molecular biologists will also benefit from a closer interaction with pathologists.

  This brings us to the end of this section on the cellular events involved in producing the cancer cell. Of course, we have a long way to go before we have full understanding, but our knowledge is advancing at an exciting pace, and a whole new language of tumour terminology is emerging. For the scientist, the battle is the biology; for the clinicians and students trying to understand and apply the new knowledge, it is often the terminology!

  The next question we need to address and one that will be in the forefront of the patient’s mind is: How will a given tumour behave? Passage contains an image

  CHAPTER 14

  THE BEHAVIOUR OF TUMOURS

  Tumour growth How do tumours spread? The biology of metastatic disease The role of the immune system

  The behaviour of a tumour can be considered under a number of headings covering how fast it will grow, whether it is likely to metastasise, which sites are affected, and what symptoms and complications the patient is likely to have.

  TUMOUR GROWTH

  It is often assumed that tumours grow faster than normal tissues because they expand to compress the surrounding structures. However, this does not mean that the cells are dividing more often, but that there is an imbalance between production and loss . The time taken for tumour cell division varies between 20 and 60 hours, with leukaemias having shorter cell cycles than solid tumours but, in general, tumour cells take longer

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  BIOS Instant Notes in Plant Biology

  • Andrew Lack, David Evans(Authors)
  • 2021(Publication Date)
  • Taylor & Francis

    (Publisher)

  Section J - Growth and Development

  J1   FEATURES OF GROWTH AND DEVELOPMENT

  Key Notes

  Growth and development

  Growth involves cell division followed by cell enlargement. Primary meristems produce files of cells in concentric rings, which form the major tissues of the plant. Development occurs when cells and tissues change form and function to give the organs and structures required during the life cycle of a plant. Growth originates with new cells formed by meristems.

  Cell Growth

  Cell Growth occurs when the cell wall is made plastic by enzymes. The driving force for cell expansion is turgor pressure, which pushes the plasma membrane out against the cell wall. The direction of growth is governed by the orientation of cellulose fibers in the wall.

  Embryogenesis

  The fertilized ovule first divides to give an apical and a basal cell. The basal cell forms the suspensor and the root cap; the apical cell gives the root, shoot and cotyledons of the seedling. Cell lineages can be traced from the seedling through the various stages of cell division, the octant stage, the dermatogen stage and the heart-shaped embryo.

  Development of tissues

  The cells laid down in the meristem form all the tissues of the plant. The first stage of development is determination, in which the cell becomes established on a pathway of change. The cell then becomes differentiated to its new function. Determination and differentiation involve altered gene expression.

  Tissue culture and totipotency

  In tissue culture, tissue explants are de-differentiated to form a callus and then redifferentiated by varying hormone or other growth conditions. Single cells in culture can be shown to be totipotent as they can regenerate to form an entire plant.

  Cell-to-cell communication

  Cell-to-cell communication occurs through plasmodesmata connecting rows or blocks of cells symplastically.

  Plant and animal development compared

  Cell walls prevent cell movements that are characteristic of animal development. Plant embryonic tissue is maintained through the life of the plant, whereas animals have a distinct embryonic stage. This gives greater plasticity of plant development. Plant cells show totipotency, the ability for single cells to regenerate an entire organism. Cell-to-cell communication in plants is limited to plasmodesmata.

  Sign up to read

  Learn more about book