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3-11 Summary

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We have moved from within prokaryotic and eukaryotic cells to the outside, and this should provide a framework for thinking about the make-up of microbes. Some ideas that you should take away from this chapter are:

  1. While not obvious in the microscope, the prokaryotic cell is organized into functional units: (i) The nucleoid organizes, manages, and replicates the DNA. (ii) The cytoplasm carries out many of the reactions of the cell including biosynthesis and catabolism. (iii) The ribosomes are the site of protein synthesis. (iv) The membrane defines the borders of the cell and serves as a barrier to most molecules. (v) The cell wall defines a microbes shape and helps protect it from the environment.
  2. The building blocks that make up the average prokaryote are also found in all living things on this planet. We share more things in common with microbes than there are features that distinguish us.
  3. Although prokaryotes are small, they have a huge amount of molecular complexity. In a sense, multicellular organisms deal with different problems by forming different cell types, but prokaryotes must adapt each cell to specific environmental conditions. They are stunningly clever little machines.

In subsequent chapters, we will learn what all these various parts are doing.

If you enjoyed this free chapter on the structure of microbes, consider buying the book, for only $30.

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Quickcheck 3-10

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1. Create a venn diagram for cell structure. Divide the diagram into cytoplasm, periplasm, and outer cell. Place as many structures in the diagram as possible. How many overlap and exist in more than one area?

2. Create a second venn diagram listing the various domains, Archaea, Bacteria, and Eukarya. Places as many structures as you can think of inside the diagram. Some of the structures will be unique to certain domains, others will span several.

3. List structures that are universal to all domains of life. Do you think this implies anything about how these cell types evolved?

4. In contrast to eukaryotes, the DNA of prokaryotes is unorganized.

  1. True
  2. False

5. Coupling of transcription and translation in prokaryotes is one reason they can respond so quickly to changes in their environment.

  1. True
  2. False

6. The ribosome is made mostly of protein

  1. True
  2. False

7. Most RNA in the cell is

  1. mRNA
  2. tRNA
  3. rRNA
  4. it depends upon cell conditions
  5. regulator RNA

8. Which of the following inclusions is involved in storing nutrients for the cell?

  1. sulfur globules
  2. polyhydroxyalkanoate
  3. gas vesicles
  4. phosphate granules
  5. magnetosomes

9. The functions of the membrane include

  1. transport
  2. motility
  3. energy generation
  4. attachment
  5. DNA synthesis

10. Explain why lipids form a membrane

11. Intracytoplasmic membranes are separate spherical blebs of membrane, not contiguous with the cell membrane, that carry out photosynthesis and other functions.

  1. True
  2. False

12. Peptidoglycan is only found in gram-positive bacteria.

  1. True
  2. False

13. LPS is only found in gram-negative cell walls

  1. True
  2. False

14. The outer membrane is a selective barrier similar to the cytoplasmic membrane.

  1. True
  2. False

15. Which of the following is not an enzyme found in the periplasm

  1. endonucleases
  2. proteases
  3. binding proteins
  4. detoxifying enzymes
  5. metabolic enzymes

16. Match the surface structure with its function

  • motility
  • attachment
  • DNA exchange
  • capsule and fimbriae
  • flagella
  • pili

17. Which of the following are resting structures that microbes create

  1. endospores
  2. cysts
  3. globules
  4. spores
  5. pancakes

18. Compare and contrast a cyst, a spore and an endospore

19. A heterocyst is a resting structure made by some cyanobacteria.

  1. True
  2. False

20. Which of the following cellular traits are only found in Archaea.

  1. Ether-linked lipids
  2. RNA polymerase has 4 proteins
  3. Pseudopeptidoglycan
  4. Cellulose in cell walls
  5. Formyl methionine as start amino acid

21. A tetraether lipid are often found in thermophilic archaea since they are stable at higher temperatures.

  1. True
  2. False

22. Match the eukaryotic structure with its function

  • photosynthesis
  • catabolism, energy generation
  • protein maturation and secretion
  • DNA replication and RNA transcription.
  • movement of parts of the cell
  • Mitochondrion
  • golgi apparatus
  • microfilaments
  • nucleus
  • Chloroplast