Supplemental Lecture (97/01/29 update) by Stephen T. Abedon (abedon.1@osu.edu)

  1. Chapter title: Eucaryote Cellular Anatomy
    1. A list of vocabulary words is found toward the end of this document
    2. Eucaryotic cells are the basic structural motif of multicelled organisms. That is, you, me, anteaters, palm trees, rose bushes, poison ivy, etc. are all multicelled organisms. Because multicelled are highly visible (i.e., they have so damn many cells you can actually see them with unaided eyes) and since we are multicelled organisms, the biology of multicelled organisms is disproportionally represented in introductory biology texts. Nevertheless, the majority of evolutionary diversity is not found among eucaryotes (indeed, the majority of eucaryote evolutionary diversity is not found among multicellular eucaryotes!).
    3. Regardless, eucaryotic cellular anatomy is fascinating if a tad overly complicated. Indeed, a tendency toward complexity is a hallmark of eucaryotes which contrasts starkly with the refinement and much more pronounced tendency toward streamlining exhibited by procaryotic cells. Additionally, it is worth knowing and understanding eucaryotic cellular anatomy, not just for academic reasons, but, as for many of us (particularly those among us with eucaryotic ancestry), practical reasons as well. If nothing else, remember this:
    4. We are eucaryotes and eucaryotes, unlike procaryotes, keep most of their DNA in membraned intracellular enclosures called nuclei (sing. nucleus). In addition, pay attention, as you read about both eucaryotes and procaryotes, to their differences. It is these differences which allow chemotherapeutics such as antibiotics to act against bacteria but not their hosts, and therefore which form the foundation of modern medicine's fight against infectious disease.
    5. Note that additional discussion of eucaryote cellular anatomy (and physiology) can be found in the lecture titled: Endomembrane System.
  2. Eucaryote
    1. An organism whose cells are nucleated.
    2. Membrane-bound organelles:
      1. In addition to a nucleus, eucaryotes may contain a number of membrane-bound organelles including: mitochondria, endoplasmic reticulum, and chloroplasts.
      2. This contrasts with procaryotes which do not contain membrane-bound organelles.
    3. Animals, plants, fungi, protozoa:
      1. Among microorganisms, fungi, protozoa, and algae are eucaryotes.
      2. Humans and other mammals (in fact, all vertebrates, animals, metazoans) are eucaryotes.
      3. See text figures 1085.1 and 1085.2 for depictions of idealized animal and plant cells.
  3. Plasma (cytoplasmic) membrane
    1. Eucaryote equivalent of the bacteria plasma membrane.
  4. Cytoskeleton
    1. The cytoplasm itself of a eucaryotic cell differs from that of a procaryotic cell in that the former contains a network of protein filaments which lend support to the cell as well as to effect cell movement (i.e., other than flagellar or ciliar movement). These filaments collectively go by the name cytoskeleton.
    2. Three protein types:
      1. Altogether, the cytoskeleton consists of three different kinds of filaments each composed a different type of protein.
      2. These proteins include:
        1. microfilaments
        2. intermediate filaments
        3. microtubules
  5. Microfilaments
    1. Microfilaments are thin actin filaments that can be varied in length to effect changes in cell shape.
    2. A commonly known result of microfilament action is the cell shape change known as amoeboid movement.
    3. This involves the extention of the cell as pseudopods</! and is involved in both movement and phagocytosis.
  6. Intermediate filaments
    1. Intermediate filaments are filaments of intermediate width (between that of microtubules, which are the thicker, and microfilaments, which are the more slender).
    2. They maintain cell shape and organelle distribution in the cytoplasm.
  7. Microtubules
    1. Microtubules are hollow, relatively thick (25 nm), and consist of the protein tubulin.
    2. Microtubules are involved in the changing of cell as well as the pulling of chromosomes to opposite ends of the cell during meiosis and mitosis.
  8. Organelle
    1. Subcellular machines:
      1. Complex, specialized, at least somewhat distinct subcellular machines, each having specific duties.
      2. Organelles are made up of proteins and other organic compounds (many of which may be additional non-proteinaceous macromolecules as well as cell membranes).
    2. Organelles in cells are analogous to organs in multi-cellular organisms. With similar analogy, organelles come in many types.
    3. See partial list of organelles below.
  9. Membrane-bound organelle
    1. Unlike procaryotic cells, eucaryotic cells have a variety of membrane-bound organelles including:
      1. the nucleus
      2. mitochondria
      3. chloroplasts
      4. endoplasmic reticulum
      5. Golgi (apparatus) complex
      6. flagella
      7. cilia
      8. lysosomes, vacuoles, etc.
  10. Flagella [sing. Flagellum]
    1. An organelle whose cell membrane covering is continuous with the plasma membrane.
    2. Effect movement:
      1. Eucaryote flagella are used to effect cellular movement.
      2. They are functionally analogous to bacterial flagella.
    3. Not structurally related:
      1. Eucaryote flagella are structurally much more complex than bacterial flagella
      2. They are not evolutionarily related to bacterial flagella.
    4. See text figure 1085.3.
  11. Cilia
    1. A shorter, more numerous (per cell) equivalent of flagella.
    2. Cilia resemble hairs projecting from the cell surface.
  12. Cell wall [pellicle]
    1. Bacteria cell wall analog:
      1. The cell wall of eucaryotes is external to the plasma membrane
      2. Like bacteria cell walls, eucaryote cell walls play roles in resisting osmotic lysis.
    2. A feature only of plants and fungi:
      1. Not all eucaryotes have cell walls (e.g., animals).
      2. In plants and some fungi the cell wall consists of cellulose.
      3. In most fungi the cell wall consists of chitin. The cell walls of yeasts consist of glucan and mannan, both polysaccharides.
      4. Protozoa, which do not have cell walls, instead have a flexible covering called a pellicle.
  13. Chromosome [chromatin]
    1. The majority of DNA of eucaryotes is found in large, linear structures.
    2. Technically, chromosomes are complex protein-linear DNA structures found only at certain points during the cell cycle (i.e., when they are visible).
    3. Eucaryote DNA is called chromatin at other times, i.e., when not visible.
    4. Eucaryote chromosomes are otherwise analogous to bacterial chromosomes.
    5. Note, however that eucaryotic chromosomes are found in an organelle called the cell nucleus.
  14. Nucleus [pl. nuclei, nuclear membrane]
    1. Double-membraned bag:
      1. An organelle surrounded by a double membrane (nuclear membrane).
      2. Encases the majority of the DNA found in eucaryotic cells.
    2. Morphology:
      1. The nucleus is a spherical or oval object in the cell cytoplasm.
      2. The nucleus frequently is very large in relation to the cell itself (though, obviously still smaller since it is contained within the cell).
    3. While most vegetative cells contain only a single nucleus, there are a number of cell types that contain two or (many) more nuclei.
    4. There are also some "cells" which lack nuclei. Terminally differentiated human red blood cells (that is, the red cells circulating in your blood) do not contain nuclei and, in fact, are better described as cellular remnants than as bona fide vegetative cells.
  15. Nuclear pores
    1. Selectively permeable pores (holes) found in the nuclear membrane.
    2. These are the passages through which RNA and ribosomes pass out of the nucleus and nuclear proteins pass in.
  16. Nucleoli [pl. nucleolus]
    1. A highly visible region (or regions) in nuclei consisting of aggregations of ribosomes and representing sites of ribosomes assembly.
    2. Nucleoli are not structures but just regions visible due to high ribosomes concentrations.
  17. Cytoplasm
    1. That part of the cell external to the nucleus and internal to the plasma membrane.
    2. Otherwise analogous to the cytoplasm of bacteria.
  18. Ribosome
    1. Very similar to bacterial ribosomes.
    2. though both larger and structurally more complex.
    3. Differences with the bacterial ribosomes allow some antibiotics to inhibit the functioning of bacterial ribosomes, but not eucaryotic ribosomes, thus killing bacteria but not the eucaryotic organisms they are infecting.
  19. Mitochondria [sing. Mitochondrion]
    1. Common organelle:
      1. Double membraned, all but "free-living" cytoplasmic organelles.
      2. Most eucaryotic cells contain more (sometimes considerably more) than one mitochondria.
    2. Mitochondria are the organelles in which cellular respiration takes place.
    3. Mitochondria more than superficially resemble the gram-negative bacteria from which they apparently evolved.
    4. For example:
      1. Mitochondria are about the size of a bacterial cell.
      2. Mitochondria are structurally similar to bacterial cells.
      3. Mitochondria have their own chromosomes which are independent of those associated with the rest of the cell as well as more similar to bacterial chromosomes than to eucaryote chromosomes.
      4. Mitochondria have their own ribosomes which are independent of those associated with the rest of the cell as well as more similar to bacterial ribosomes than to eucaryote ribosomes.
    5. Characteristics:
      1. Mitochondria display the following anatomical characteristics:
        1. matrix:The interior of mitochondria, cytoplasm equivalent.
        2. inner membrane:The mitochondria plasma membrane equivalent.
        3. crista (pl. cristae):Radical foldings of the mitochondria inner membrane which probably serve to all the packing of more inner membrane proteins into a given mitochondria.
        4. outer compartmentThe mitochondria periplasmic space equivalent.
        5. outer membraneThe mitochondria outer membrane equivalent.
  20. Chloroplast
    1. An organelle analogous to mitochondria except in which photosynthesis occurs (i.e., not cellular respiration).
  21. Vacuole
    1. Various plant membrane-enclosed compartments serving different functions (protein and waste storage, for example) depending on the cell types within which they are found.
  22. Vocabulary
    1. Chloroplast
    2. Chromosome
    3. Cilia
    4. Cytoplasm
    5. Cytoplasmic membrane
    6. Cytoskeleton
    7. Eucaryote
    8. Flagella
    9. Intermediate filaments
    10. Microfilaments
    11. Microtubules
    12. Mitochondria
    13. Nuclear membrane
    14. Nucleus
    15. Organelle
    16. Plasma membrane
    17. Ribosome
    18. Vacuole
    19. See also Lecture: Endomembrane System
  23. Practice questions
    1. In eucaryotic cells, the matrix occupying the volume between the nucleus and the cell membrane is known as the ___________. [PEEK]
    2. Which of the following features is normally found in eukaryotic cells but is never found in bacterial cells? (circle correct answer) [PEEK]
      1. cell wall
      2. cytoplasm
      3. lipids
      4. nuclear membrane
      5. all of the above
      6. none of the above
    3. What is the function of the nucleolus? (circle correct answer) [PEEK]
      1. import of cytoplasmic proteins
      2. regulation of nuclear pores
      3. site of ribosome assembly
      4. storage of inactive DNAs
      5. synthesis of nuclear proteins
      6. all of the above
      7. none of the above
    4. Where do the mitochondria in a living cell come from? (circle correct answer) [PEEK]
      1. division of preexisting mitochondria
      2. elaboration from vesicles produced by ER
      3. engulfing anaerobic bacteria from the environment
      4. Golgi
      5. ribosomes from the nucleus, using nuclear DNA
      6. all of the above
      7. none of the above
    5. Which of the following structures is external to the plasma membrane. (circle one correct answer) [PEEK]
      1. eucaryote flagella.
      2. eucaryote cilia.
      3. mitochondria.
      4. cell wall.
      5. all of the above.
      6. none of the above.
    6. Name two ways bacteria chromosomes differ from eucaryotic chromosomes. [PEEK]
    7. __________ typically pass through nuclear pores. (circle one correct answer) [PEEK]
      1. nucleoli (in toto).
      2. vesicle proteins.
      3. DNA.
      4. mitochondria.
      5. all of the above.
      6. none of the above.
    8. Match the mitochondria and Gram-negative bacteria equivalents by placing the appropriate Roman numeral in each of the blanks below: (a) inner membrane, (b) matrix, (c) outer membrane, (d) cristae, (e) outer compartment: (fill in blanks appropriately; do not use numerals more than once; hint, the periplasm is a volume found between the inner and outer membranes of Gram-negative bacteria) [PEEK]
      1. _____ periplasmic space.
      2. _____ surface-area-increasing folds.
      3. _____ cytoplasm.
      4. _____ inner membrane.
      5. _____ outer membrane.
  24. Practice question answers
    1. cytoplasm
    2. iv, nuclear membrane
    3. iii, site of ribosome assembly
    4. i, division of preexisting mitochondria
    5. iv, cell wall.
    6. eucaryote chromosomes are (i) larger, (ii) linear rather than circular, (iii) are found in greater numbers per cell, (iv) are found in nuclei, (v) are visible through light microscopes at certain times during the cell cycle (bacteria chromosomes are not)
    7. vi, none of the above.
    8. vi, none of the above.
    9. i:e, ii:d, iii:b, iv:a, v:c.
  25. References
    1. Benjamin, C.L., Garman, G.R., Funston, J.H. (1997). Human Biology. The McGraw-Hill companies, New York, pp. 69-70.
    2. Raven, P.H., Johnson, G.B. (1995). Biology (updated version). Third Edition. Wm. C. Brown publishers, Dubuque, Iowa. pp. 85-106.
    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. 90-102.