Supplemental Lecture (98/03/28 update) by Stephen T. Abedon (abedon.1@osu.edu)

  1. Chapter title: Procaryote Cytoplasmic Organelles
    1. A list of vocabulary words is found toward the end of this document
  2. Procaryote [prokaryote]
    1. A procaryote is an organism whose cells:
      1. lack a nuclear membrane surrounding their DNA
      2. lack additional membrane-bounded organelles.
    2. Profound differences:
      1. Though simple enough to state, these differences result in profoundly differently functioning cells (i.e., contrast procaryote with eucaryote).
      2. (Tortora et al., 1995 lists three additional differences between procaryotes and eucaryotes; p. 70; see also Raven & Johnson, 1995, p. 86-87)
    3. Among microorganisms, the following are procaryotes:
      1. bacteria
      2. cyanobacteria
      3. archaeobacteria
      4. mitochondria
      5. cloroplasts
    4. Additional characteristics of procaryotes:
      1. Procaryotic cells have various characteristics, many of which are discussed here.
      2. Note that not all of the characteristics associated with some bacteria are associated with all procaryotes. For example, not all bacteria have:
        1. glycocalyx
        2. flagella
        3. fimbriae
        4. pili
        5. etc.
  3. Cytoplasm [protoplasm]
    1. The inside of a procaryotic (or eucaryotic) cell.
    2. Basically the cytoplasm is a complex water solution full of biologically relevant molecules which is contained by the plasma membrane (which is also known as the cytoplasmic membrane).
  4. Bacterial chromosome [genophore]
    1. The molecule containing the majority of the DNA in the bacterial cell.
    2. Properties:
      1. The Bacterial chromosome has the following properties:
        1. it is circular
        2. it is double-stranded
        3. there is only one copy*
      2. *Unless chromosome replication has gotten ahead of cell replication.
      3. Note that eucaryotes, too, have chromosomes, though the eucaryotic chromosome, other than also consisting of double stranded DNA, is otherwise structurally unrelated to the bacterial chromosome (i.e., eucaryotic chromosomes are linear and often consist of more than one copy per cell).
    3. Most of the proteins found in a bacteria are coded by genes found on the bacterial chromosome.
  5. Plasmid
    1. Bacteria can contain additional circular, double-stranded pieces of DNA. These tend to be much smaller than the bacterial chromosome and have a copy number greater than one.
    2. Plasmid proteins:
      1. Plasmids can code for some cellular proteins.
      2. Plasmid coded proteins tend to be dispensable to the cell, at least in some environments.
    3. Antibiotic resistance:
      1. Significantly, genes that code for antibiotic resistance tend to be carried by plasmids.
      2. Resistance or "R factors present very serious problems for the treatment of infectious diseases with antibiotics. The wide-spread use of antibiotics in medicine and agriculture (many animal feeds contain antibiotics) has led to he preferential survival (selection) of bacteria that have R factors, so populations of resistant bacteria grow larger and larger. The transfer of resistance between bacterial cells of a population, and even between bacteria of different genera, also contributes to the problem." (p. 217, Tortora et al., 1995)
  6. Ribosome
    1. Complex translation machines:
      1. Extremely large, complex protein-RNA structures charged with converting the code contained in messenger RNA into the code contained in polypeptides (translation).
      2. Bacterial ribosomes may be found free-floating in the cytoplasm or as membrane-bound structures.
      3. The latter is analogous to the ribosomes found on the eucaryote rough endoplasmic reticulum, and similarly involved in membrane and secreted protein synthesis.
    2. Ribosomes consist of ribosomal RNA and ribosomal proteins.
    3. Ribosomes are the most expensive multi-copy items found in bacterial cells (cell envelopes and chromosomes are considered to be single-copy items for this argument).
    4. Target for antibiotics:
      1. As a consequence of eucaryote and procaryote ribosomes subtlely differing structurally (they are called 70S and 80S ribosomes, respectively), a variety of antibiotics interfere with bacterial ribosomes but not eucaryotic ribisomes.
      2. Examples of such antibiotics include: Cloramphenicol, cycloheximide, erythromycin, puromycin, streptomycin, and tetracycline.
  7. Inclusions [granules]
    1. Deposits (often in reserve) of a variety of substances.
    2. Certain types of deposits can be relatively visible inside certain types of bacteria thus allowing identification.
    3. Note that some inclusions are actually membrane-bound, though the membranes are single rather than double layered (i.e., not lipid bilayers so technically not considered to be "membrane"-bound organelles).
  8. Links
    1. ribosomes
  9. Vocabulary
    1. bacterial chromosome
    2. cytoplasm
    3. inclusions
    4. plasmid
    5. procaryote
    6. ribosome
    7. See also Lecture: Procaryotic Cellular Anatomy I.
  10. Practice Questions
    1. Which of the following is not true? [PEEK]
      1. procaryotes lack nuclei
      2. cyanobacteria are procaryotes
      3. blue-green algae are procaryotes
      4. mitochondria are procaryotes
      5. all procaryotes have plasma membranes
      6. all of the above are "not true"
      7. none of the above are "not true"
    2. Tetracycline interferes with the action of bacterial ribosomes. Specifically what will a cell fail to produce as a direct consequence of tetracycline activity? (one word answer) [PEEK]
    3. Because of its action on __________, tetracycline (as well as Cloramphenicol) can be toxic to humans. (one word answer) [PEEK]
      1. mitochondria
      2. plasma membranes
      3. DNA
      4. Cytoplasm
      5. glycocalyx
      6. cell walls
    4. Name two differences between a bacterial plasmid and a bacterial chromosome. [PEEK]
    5. What is a plasmid? (define giving three characteristics) [PEEK]
    6. Name a category of gene functions often associated with plasmids, ones that makes knowledge of plasmids especially important to an understanding of modern medical microbiology. [PEEK]
  11. Practice question answers
    1. vii, none of the above are "not true"
    2. proteins.
    3. mitochondria.
    4. The plasmid is smaller, expendable, and transferable, the chromosome is larger, not expendable, and generally much less transferable.
    5. an extrachromosomal, circular piece of DNA found in the cytoplasm of bacteria
    6. antibiotic resistance
  12. References
    1. Black, J.G. (1996). Microbiology. Principles and Applications. Third Edition. Prentice Hall. Upper Saddle River, New Jersey. pp. 78-82, 84-90.
    2. Prescott, L.M., Harley, J.P., Klein, D.A. (1996). Microbiology. Third Edition. Wm. C. Brown Publishers, Dubuque, IA. pp. 40-72.
    3. Tortora, G.J., Funke, B.R., Case, C.L. (1995). Microbiology. An Introduction. Fifth Edition. The Benjamin/Cummings Publishing, Co., Inc., Redwood City, CA, pp. 70-90.