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Chapter 17

Chapter Study Questions

Chapter Study Questions


This activity contains 18 questions.

	Match the key terms in this chapter listed below with the phrase that is the best match for it. Using the pull-down menus, match each item in the left column to the corresponding item in the right column. RNA World lateral, or horizontal, gene transfer cenancestor, or LUCA, or last universal common ancestor Oparin-Haldane model ribozyme 1.1 the last common ancestor of all living organisms A B C D E 1.2 an enzyme that is made of RNA rather than of protein A B C D E 1.3 a hypothetical time when life on Earth was based on RNA A B C D E 1.4 a model that proposes that the early Earth possessed all the necessary ingredients for the origins of life. A B C D E 1.5 movement of a gene from one species or lineage to another A B C D E

	Some of the following statements represent evidence that early life was once based on RNA. Which ones?   The most highly conserved component of metabolic machinery is the ribosome, which is built on an RNA framework. In modern cells, the basic currencies for biological energy are deoxyribonucleoside triphosphates. In modern cells, RNA catalyzes protein synthesis. In modern cells, RNA catalyzes the replication of DNA. RNA is the only known molecule that carries genetic information and also can catalyze chemical reactions.

	What were the first self-replicating entities on Earth probably made of?   proteins RNA (the "RNA World") thioesters, clays, or some other simple replicating system that preceded the RNA World self-replicating phospholipid membranes DNA

	Why are neither proteins nor DNA considered likely to have been the first life forms?   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.

	RNA populations in the lab have evolved all of the following abilities except one. Which one?   replicate themselves form peptide bonds catalyze carbon-carbon bonds bind tightly to certain other molecules cleave DNA link a pair of adjacent RNA molecules

	Which statements are reasonable conclusions from the data shown in this figure representing Bartel and Szostak's experiment on RNA evolution?   Ten rounds of selection caused a ten-million-fold increase in catalytic rate. RNA molecules can evolve in solution. This experiment proves that it is possible for RNA molecules to evolve to replicate themselves. The increase shown was probably due to genetic drift. This experiment proves that it is possible for RNA molecules to evolve the ability to catalyze bonds between adjacent RNA subunits.

	Which statements are correct?   The oldest rocks that contain any signs of life are 3.7-3.85 billion years old. The oldest fossils ever found are 2 billion years old and appear similar to embryos. The oldest fossils ever found, though they are controversial, may be 3.2-3.5 billion years old. Few rocks older than 2.5 billion years still exist on Earth; any fossils from before that time are unlikely to have survived. The oldest fossils ever found appear similar to bacteria and are 3.85 billion years old. The oldest signs of life found in any rocks are microscopic crystals with distinctive oxygen isotope ratios that are characteristic of living organisms.

	It has been difficult to determine the relationships of the three domains of life to each other, due to the occurrence of extensive horizontal gene transfer. However, the best guess, based on analyses of whole genomes is that the domains _______ and ______ are more closely related to each other than either is to the domain _______.   Bacteria; Eukarya; Archaea Archaea; Bacteria; Eukarya Eukarya; Archaea; Bacteria

	Why is the last recent common ancestor now considered to have been a community of interbreeding species, and not a single species?   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.

	Match each hypothesis listed below with the description that is the best match for it. Using the pull-down menus, match each item in the left column to the corresponding item in the right column. universal gene-exchange pool hypothesis three viruses, three domains hypothesis ring of life hypothesis chronocyte hypothesis 10.1 Modular genomes exchanged genes and proteins readily with each other; organisms assembled their genomes piecemeal from the environment, not by self-replication. A B C D 10.2 The first eukaryote arose as a fusion of an archaean with a bacterium. A B C D 10.3 The first eukaryote was a member of a long-vanished lineage that ate an archaean, which became the nucleus. A B C D 10.4 Bacteria, archaeans and eukaryotes all used to use RNA; they were converted to DNA by different viruses. A B C D

	Spiegelman et al. demonstrated that QB RNA changed over the course of many serial transfers from one test tube system to another. Given all their findings, which of the following best explains the changes they observed?   Selection favored changes in the RNA that allowed it to be replicated more quickly. Because only a small amount of RNA was transferred at a time, genetic drift (sampling error) is most likely responsible for the differences observed. The experimental protocol allowed mutations to take place. Therefore, mutation-selection balance is the best explanation. The first two choices are both correct.

	In what important way did Beaudry and Joyce extend the work done on RNA evolution by Spiegelman and colleagues?   Because of the nature of their experimental system, they were able to identify the specific mutations that increased fitness in their experimental RNA populations. They were able to impose selection pressure on their RNA molecules, where Spiegelman et al. were not. They were able to demonstrate that spontaneously mutating RNA could catalyze the formation of double-stranded DNA molecules. The first three choices are all correct.

	In one or two brief sentences, give your own interpretation of what Gerald Joyce meant when he wrote that "Once an RNA enzyme with RNA replicase activity is in hand, the dreaming stops and the fun begins."   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.

	The interpretation that the amino acids found in the Murchison meteorite were, in fact, extra-terrestrial in origin came from what line(s) of evidence?   The scientists who studied the amino acids cracked the meteorites in the lab and took samples only from the interior. Thus, they were sure their samples weren't contaminated by amino acids picked up after the meteorite landed. The amino acids sampled occurred in both isomeric forms in about the same proportions, whereas amino acids in living things occur only in one form. Two of the amino acids aren't found in any organism on Earth. Thus, they must have been produced elsewhere. The first two choices are both correct.

	Although chemists have had some success in identifying plausible mechanisms for the prebiotic synthesis of amino acids, sugars, and nitrogenous bases, the "warm little pond" that molecular biologists dream about is still a "prebiotic chemist's nightmare." Why?   Prebiotic synthesis of these building blocks produces both mirror-image isomers of each kind of chemical; living things use only one isomer. The building blocks that form polymers must be chemically charged, or activated, before they can be joined into a polymer; this requires a source of chemical energy. The ribose sugar currently used by RNA forms a very small percentage of the sugars that can form from formaldehyde condensation (the prebiotic pathway proposed for the production of ribose). The first three choices are all correct.

	The second step in the Oparin-Haldane model is the formation of biological polymers from building blocks in the prebiotic soup. Although polymer synthesis can happen in water, so does _____. Ferris et al. have proposed a solution to this problem by demonstrating that _____ can act as a catalyst, speeding up the rate of polymer formation.   hydrolysis/clay enzymatic breakdown/clay mutation/enzymes condensation/clay

	The figure illustrates a universal phylogeny based on the HMGCoA reductase gene. Archaeoglobus fulgidus is unambiguously an archaean, but it is placed in the Bacteria based on its HMGCoA sequence. The most parsimonious explanation for this pattern is that A. fulgidus acquired a bacterial HMGCoA gene by .

	Based on the dates of the oldest known fossils of eukaryotes and cyanobacteria, the first branching in the universal phylogeny most likely took place no more recently than   2 million years ago. 1 million years ago. 200,000 years ago. 2 billion years ago.

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