Chapter 3 Cell Structure and Function Essay Questions

3.4 Essay Questions 1) Compare and contrast the characteristics of prokaryotic and eukaryotic cells. Answer: Prokaryotic cells have a nucleoid, a region within the cytoplasm where the DNA is found, but this region is not surrounded by a membrane. Eukaryotic cells, however, have a true nucleus that is surrounded by a nuclear membrane. Additionally, eukaryotic cells have a variety of membranous compartments known as organelles within the cell, whereas prokaryotes do not have membranous organelles. Prokaryotic cells tend to be smaller and less structurally complex in general than eukaryotic cells. Even though the two types of cells may have various structures in common, such as cell walls and flagella, these structures can vary widely in their molecular composition. Bloom's Taxonomy: Application Section: Prokaryotic and Eukaryotic Cells: An Overview Learning Outcome: 3.2 2) Compare and contrast archaea and bacteria, with particular attention to the features that lead to their placement in separate taxa. Answer: Bacterial cell walls are composed of peptidoglycan, whereas archaeal cell walls are composed of a variety of carbohydrate forms but never peptidoglycan. The flagella of the two groups of prokaryotes have several differences, including size, manner of assembly, and function. Although both have fimbriae, archaea have a distinctive attachment structure called a hamus that is somewhat like a barbed grappling hook. Bacterial cytoplasmic membranes may contain hopanoids, archaeal cytoplasmic membranes do not. The ribosomes of archaea and bacteria are of similar size, but some ribosomal components of archaea are more like those of eukaryotic ribosomes than those of bacteria. RNA metabolism in the two prokaryotic groups differs, and the archaeal genetic code is more like that of eukaryotes than that of bacteria. Archaeal phospholipids are different from bacterial and eukaryotic phospholipids in that the glycerol is a stereoisomer, the linkages are ether instead of ester between hydrocarbon chains and glycerol, the hydrocarbon chains are isoprene chains rather than fatty acids, which are branched rather than linear, as the fatty acids are. Bloom's Taxonomy: Analysis Section: Cytoplasm of Archaea Learning Outcome: 3.24, 3.25, 3.26, 3.27, 3.28, 3.29 3) Most antibacterial drugs disrupt or destroy bacterial cellular characteristics that are different from those of eukaryotic cells or that may not even be present in eukaryotic cells, an idea termed 'selective toxicity'. List and describe at least three cellular features of bacteria that could be targeted to inhibit or kill a bacterial pathogen. Answer: 1. Cell wall: The cell wall of almost all bacteria contains peptidoglycan, a molecule absent in eukaryotic cell walls. Gram-negative cell walls contain unique molecules such as lipopolysaccharide and structures such as porins, which are not present in eukaryotic cells. Additionally, human cells do not have a cell wall at all. 21 2. Ribosomes: Bacterial ribosomes have a 70S structure, whereas eukaryotic ribosomes have an 80S structure. This difference is enough to allow some drugs to preferentially affect bacterial ribosomes while leaving eukaryotic ribosomes unharmed. 3. Cellular appendages: Although both prokaryotic and eukaryotic cells can have flagella, the two types of cells use structurally different types of flagella. Furthermore, many bacteria have fimbriae and pili, which are not found on eukaryotic cells. 4. Cell membrane: Most cells use a phospholipid bilayer with inserted proteins as a cell membrane; however, bacterial cell membranes may contain hopanoids, which are absent in eukaryotic cell membranes. Bloom's Taxonomy: Analysis Section: Cytoplasm of Eukaryotes Learning Outcome: 3.31, 3.34, 3.36, 3.40 4) Both mitochondria and chloroplasts have inner membranes with much greater surface area than their outer membranes. Discuss the contribution of the extensive inner membranes to the roles of these organelles. Answer: Both organelles use metabolic processes embedded in lipid membranes to produce cellular energy. The cristae of mitochondria produce ATP. The thylakoids of chloroplasts are the site of light energy capture and conversion to cellular energy. The extensive surface area of the folded inner membranes allows both organelles to produce much more energy than would otherwise be possible. Bloom's Taxonomy: Application Section: Cytoplasm of Eukaryotes Learning Outcome: 3.42 5) Describe how the structure of the bacterial cytoplasmic membrane relates to its function of selective permeability. Answer: The structure and function of the cytoplasmic membrane are explained in the fluid mosaic model. The cytoplasmic membranes of bacterial cells are composed of phospholipids, which create a semipermeable barrier to the cell's outer environment. The only molecules that can easily cross the membrane are small, lipid soluble molecules. Other types of molecules must use the wide variety of transport proteins embedded in the phospholipid bilayer to cross the membrane. In this way, the cell can control the concentration of both its nutrients and its waste products. The cytoplasmic membrane can also be used for energy production and for photosynthesis in prokaryotic cells. Bloom's Taxonomy: Application Section: Bacterial Cytoplasmic Membranes Learning Outcome: 3.15 22