Victory for the ACT Student Text 15e

130 • R EADING transformation was a stable genetic change. ˜‡”› ƒ† Š‹•…‘Ǧ™‘”‡”• ’—”‹ϐ‹‡† –Š‡ contents of cells in detergent after their disruption and found that among the …‘–‡–• ‘ˆ –Š‡…‡ŽŽ•ǡ ‘Ž› –Š‡ ’—”‹ϐ‹‡† was capable of causing the transformation. As a result of these and future experiments, it was determined that in order for transformation to occur, DNA fragments entered the recipient cell intact and substituted in the bacterial chromosome for the original DNA, which was eliminated. This process resulted in the creation of a genetically different microorganism. ‹• ƒ ˜‡”› Ž‘‰ǡ ϐ‹„”‘—• ‘Ž‡…—Ž‡ with a backbone composed of alternate sugar and phosphate groups joined by 3’-5’-phosphodiester linkages. Attached to each sugar is one of four possible nitrogenous bases. There are two types of bases: the pyrimidines, cytosine (C) and thymine (T); and the purines, adenine (A) and guanine (G). The amount of purine equals the amount of pyrimidine, and, more •’‡…‹ϐ‹…ƒŽŽ›ǡ –Š‡ ƒ‘—– ‘ˆ ƒ†‡‹‡ ‡“—ƒŽ• the amount of thymine, and the amount of guanine equals the amount of cytosine. In 1953, Franklin, Watson, and Crick proposed that DNA was made of two chains of nucleotides coiled around a common axis, with the sugar-phosphate backbone on the outside and the bases pointing in toward the axis, and that the two chains were held together by hydrogen bonds. The hydrogen bonds occur between each base of one chain and an associated base on the other chain. Based on the 20-angstrom width of –Š‡ ϐ‹„‡”ǡ ƒ ’›”‹‹†‹‡ ˆ”‘ ‘‡…Šƒ‹ ‹• always paired with a purine from the other chain. Adenine is the only purine capable of bonding to thymine and guanine is the only purine capable of bonding to cytosine. Franklin, Watson, and Crick proposed that the information in DNA was coded for by the linear sequence of the base pairs. They theorized that a mutation could be accounted for by a chance mistake in the formation of the sequence during duplication. Another major aspect of the Watson and Crick model was the proposed complementarity between hydrogen- bonded nucleotides. For example, adenine is complementary to thymine, AGC is complementary to TCG, and one chain is complementary to the other. If the base sequence of one chain is known, then 60 65 70 75 80 85 90 95 100 105 110 Map It Out If you are a visual learner, mapping out or diagramming the relationships or things described in a Natural Science passage can help you organize your thoughts and clarify your understanding of the passage. These diagrams will become especially helpful for explicit detail or simple inference questions which may refer back to the relationships or things described. Passage Perfect In questions like item #28, you must pay attention to all of the “—ƒŽ‹ϐ‹…ƒ–‹‘• listed in the question. The correct answer choice will both ͳȌ ”‡ϐŽ‡…– ƒ departure in ’ƒ”ƒ‰”ƒ’Š ϐ‹˜‡ from the paragraphs preceding it and 2) describe the primary intention ‘ˆ ’ƒ”ƒ‰”ƒ’Š ϐ‹˜‡Ǥ DO NOT select an answer choice that only meets one of these “—ƒŽ‹ϐ‹…ƒ–‹‘•Ǥ

the base sequence of the complementary chain can be derived. The concept of complementarity of nucleic acids in DNA and RNA chains is the basis of most research in which these classes of molecules are involved. 23. Mendel conducted his studies using the method known as: A. cloning. B. genetic mapping. C. cross-pollination. D. transformation. 24. ‡†‡Žǯ• ϐ‹†‹‰• ™‡”‡ ‹’‘”–ƒ– „‡…ƒ—•‡ they indicated which of the following? I. DNA fragments can replace original DNA. Ǥ ’‡…‹ϐ‹…—‹–•ǡ Šƒ†‡† †‘™ from one generation to the next, govern traits in organisms. III. Proteins are composed of approximately 20 different amino acids. F. I only G. II only H. I and III only J. I, II, and III 25. Contrary to earlier beliefs, Avery et al. discovered that: A. there are only four nucleotides in DNA. B. pneumonia can be passed from host to host. C. genes can mutate. D. DNA, not protein, carries genetic information. 26. If you infected R strain pneumococcus with S extract and saw a few R strain pneumococcus transformed to S strain, you would expect: F. the remaining R strain pneumococcus to transform later. G. only the new S strain cells to survive. H. offspring of those transformed cells to be S strain as well. J. a few S strain pneumococcus to transform to R strain. 115