the common progenitor of these groups existed very early in evolution. Analysis and classification of the archaea has fundamentally changed how biologists think about organismal diversity. Key Takeaways 1. Archaea are a different life form, as different from bacteria as we are from E. coli . 2. Archaea share traits that are similar to eukaryotes. The RNA polymerase of Archaea and the promoter structure is similar to eukaryotes. 3. In addition, translation of proteins inserts a methionine as do eukaryotes, instead of a formylmethionine, as bacteria do. 4. Archaea do have some unique traits, including ether-linked lipids and unique cell wall structures that can be formed from pseudopeptidoglycan or an S-layer. Chapter 3-9 Eukaryotic cells have a lot in common with Prokaryotic cells
This section will focus on describing some of the differences between Bacteria and Eukarya. It will not be an exhaustive review of eukaryotic structure, as you have learned this material in your high school or college biology class. After the recent journey through the bacterial cell, you may have started to wonder about your own cells or other eukaryotic cells. How many properties do we share with bacteria? How are we different? It turns out, as you might expect, we share some basic things in common, but other structures are very different. Figure 3.40. Comparison of cytochrome oxidase from bacteria and bovine. . Molecular models of cytochrome oxidase from Rhodobacter sphaeroides (A) and bovine (B) are compared. Each protein is a complex of several distinct proteins, but the four polypeptides shown in color have a high degree of similarity in both their sequence (see Figure 3.41) and structure. The structural similarity should be obvious in this view. Such structurally similarity cannot have arisen by chance, but must reflect the evolution of each from a single ancestor. The gray polypeptides in the bovine cytochrome oxidase are not found in the bacterial protein. The basic building blocks of the cell, such as nucleic acids, amino acids and sugars are identical. Macromolecular organizations such as chromosomes and membranes have many similarities. Many proteins in eukaryotes, especially those that carry out essential cell functions, have homologs in bacteria that share a high degree of sequence and structural similarity. An example that illustrates this point is the respiratory enzyme cytochrome oxidase. As shown in Figures 3.40 and 3.41, a comparison of cytochrome oxidase from the bovine and Rhodobacter sphaeroides reveals a near identical arrangement of the catalytic proteins and high sequence similarity. However, the cytochrome oxidase in the bovine has a number of other polypeptides that serve a structural role.
Figure 3.41. Sequence comparison of cytochrome oxidase from three species . A sequence comparison of cytochrome oxidase showing the high degree of identical amino acids between these very different species: cows and two different bacteria. The colored boxed indicate where the amino acids are identical or similar among the three sequences and the different colors refer to different classes of amino acids.
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- Spring '08