Binary Fission in Bacteria

4 Key excerpts on "Binary Fission in Bacteria"

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  eBook - ePub

  Bacteria and Viruses

  • Britannica Educational Publishing, Kara Rogers(Authors)
  • 2010(Publication Date)
  • Britannica Educational Publishing

    (Publisher)

  Asexual reproduction, in the form of binary fission, budding, or sporulation, represents the primary mode of reproduction utilized by bacteria. Asexual reproduction is augmented by genetic exchange, which occurs via three different mechanisms: transformation, transduction, or conjugation. In these processes, bacteria may take up genetic material freely (transformation), may receive genetic material from a special type of bacteria-infecting virus (transduction), or may temporarily combine physically with other bacterial cells to swap genes (conjugation).

  BINARY FISSION

  Most prokaryotes reproduce by a process of binary fission, in which the cell grows in volume until it divides in half to yield two identical daughter cells. Each daughter cell can continue to grow at the same rate as its parent. For this process to occur, the cell must grow over its entire surface until the time of cell division, when a new hemispherical pole forms at the division septum in the middle of the cell. In Gram-positive bacteria the septum grows inward from the plasma membrane along the midpoint of the cell; in Gram-negative bacteria the walls are more flexible, and the division septum forms as the side walls pinch inward, dividing the cell in two. In order for the cell to divide in half, the peptidoglycan structure must be different in the hemispherical cap than in the straight portion of the cell wall, and different wall cross-linking enzymes must be active at the septum than elsewhere.

  BUDDING

  A group of environmental bacteria reproduces by budding. In this process a small bud forms at one end of the mother cell or on filaments called prosthecae. As growth proceeds, the size of the mother cell remains about constant, but the bud enlarges. When the bud is about the same size as the mother cell, it separates. This type of reproduction is analogous to that in budding fungi, such as brewer’s yeast (Saccharomyces cerevisiae ). One difference between fission and budding is that, in the latter, the mother cell often has different properties from the offspring. In some Pasteuria strains, the daughter buds have a flagellum and are motile, whereas the mother cells lack flagella but have long pili and holdfast appendages at the end opposite the bud. The related Planctomyces , found in plankton, have long fibrillar stalks at the end opposite the bud. In Hyphomicrobium

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  eBook - ePub

  Biology

  A Self-Teaching Guide

  • Steven D. Garber(Author)
  • 2020(Publication Date)
  • Jossey-Bass

    (Publisher)

  3 Cell Division

  CELLULAR REPRODUCTION

  To create more cells and more living organisms, cells reproduce. However, simply dividing in half is not sufficient. Since it is imperative that each cell passes along its genetic information to succeeding generations of cells when a cell reproduces, each daughter cell must receive more than just a portion of the vital information; a complete copy of all the essential genetic material is necessary.

  Some mechanism is needed to pass on all a cell's chromosomal information to its daughter cells. Therefore, before dividing, the parent cell must produce a copy of all the required information. This duplication is also called replication; both words are used interchangeably when discussing cell division.

  Cells, though similar, aren't all identical, and neither are the mechanisms they use to divide. Prokaryotes are thought to represent the most primitive living forms of cells. They divide in a manner that is less complex than the more advanced eukaryotes.

  Prokaryotic Cell Division: Binary Fission

  Prokaryotic cells have one circular chromosome. When the chromosome duplicates, each of the resulting copies moves to a separate end of the cell, and a membrane forms in the middle of the parent cell, dividing it into two parts. Those two parts then separate, creating two daughter cells; each daughter cell contains an entire set of genetic material. This process of prokaryotic cell division is called binary fission (see Figure 3.1 ).

  Eukaryotic Cell Division

  Eukaryotic cell division involves a series of steps that are distinct from the process that occurs in prokaryotes. These steps include the division of the nucleus, known as karyokinesis, as well as the division of the rest of the cell, which is called cytokinesis.

  Before the cell begins to divide, the genetic information located in the nucleus in the form of chromosomes must be duplicated. The chromosomes are the structures in the cells that contain the greens. All the instructions concerning the life processes of a cell emanate from the chromosomes. At the ends of the chromosomes are regions of repetitive DNA called telomeres

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  Environmental Microbiology for Engineers

  • Volodymyr Ivanov(Author)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)

  8

  Reproduction, Proliferation, and Growth

  Reproduction of Viruses

  The reproduction of viruses is defined as an increase in the number of viral particles. There are six basic stages in viral reproduction:

  1. 1. attachment: a specific binding between virus and host cell, determining the host range of the virus
  2. 2. penetration: when the attached virus enters the host cell
  3. 3. uncoating: when the viral envelope is degraded, thus releasing the viral nucleic acid
  4. 4. replication: synthesis of viral nucleic acid and protein
  5. 5. self-assembly of the virus particles
  6. 6. lysis of the host cell and the release of viruses

  Reproduction of Prokaryotes

  Reproduction is defined as an increase in the number of cells. Growth is defined as an increase in biomass.

  The most common method of cell reproduction in Bacteria and Archaea groups is an increase in cell volume, followed by the binary fission of the adult cell to two almost equal daughter cells (Figure 8.1 ).

  FIGURE 8.1 Reproductive cycles of (a) rod-shaped and (b) spherical prokaryotic cell by binary fission.

  Other, less common methods of cell reproduction include multiple fission or budding (Figure 8.2 ). In this case, mother and daughter cells have quite different sizes, shapes, and other properties.

  FIGURE 8.2 Reproductive cycles of prokaryotic cells with multiple fission (a and b) or budding (c). The bud is formed on a mother cell. The bud then grows and is transformed into a daughter cell that is separated from the mother cell.

  Vegetative Reproduction of Microscopic Eukaryotes

  The reproduction of microscopic eukaryotes is either performed by vegetative reproduction, which starts with the growth of cell biomass and is followed by the separation of mother and daughter cells, or by other methods of asexual and sexual reproduction.

  For example, vegetative reproduction of mycelial fungi takes place by the elongation and separation of cells at the tip of the hyphae. The network of hyphae, mycelium, is an effective structure for penetrating the soil and adsorbing nutrients from the terrestrial environment. Mycelial fungi grow by the elongation of the hyphae at their tips. Nutrients adsorbed by mycelium are distributed between the cells of the mycelium.

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  Molecular Biology

  • David P. Clark(Author)
  • 2009(Publication Date)
  • Academic Cell

    (Publisher)

  Chapter Eighteen

  Bacterial Genetics

  Reproduction versus Gene Transfer Fate of the Incoming DNA after Uptake Transformation is Gene Transfer by Naked DNA Transformation as Proof that DNA is the Genetic Material Transformation in Nature Gene Transfer by Virus—Transduction Generalized Transduction Specialized Transduction Transfer of Plasmids between Bacteria Transfer of Chromosomal Genes Requires Plasmid Integration Gene Transfer among Gram-Positive Bacteria Archaebacterial Genetics Whole Genome Sequencing

  Reproduction versus Gene Transfer

  Sex and reproduction are not at all the same thing in all organisms. In animals, reproduction normally involves sex, but in bacteria, and in many lower eukaryotes, these are two distinct processes. Bacteria divide by binary fission . First they replicate their single chromosome and then the cell elongates and divides down the middle. No resorting of the genes between two individuals (that is, no sex) is involved and so this is known as asexual or vegetative reproduction .

  In bacteria, cell division and the re-assortment of genetic information are completely separate processes.

  From a biological perspective, sexual reproduction serves the purpose of reshuffling genetic information. This will sometimes produce offspring with combinations of genes superior to those of either parent. Although bacteria normally grow and divide asexually, gene transfer may occur between bacterial cells. During sexual reproduction in higher organisms, germ line cells from two parents fuse to form a zygote that contains equal amounts of genetic information from each parent. In contrast, in bacteria gene transfer is normally unidirectional and cell fusion does not occur. Genes from one bacterial cell are donated to another. We thus have a donor cell that donates DNA and a recipient cell that receives the DNA.

  The transfer of genes between bacteria fulfils a similar evolutionary purpose to the mingling of genes during sexual reproduction in higher organisms. However, mechanistically it is very different. Consequently, some scientists regard bacterial gene transfer as a primitive or aberrant form of sex, whereas others believe that it is quite distinct and that use of the same terminology is misleading.

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