Ch09 - Chapter 9 9.1(a How did the transformation experiments of Griffith differ from those of Avery and his associates(b What was the significant

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Chapter 9 9.1 (a) How did the transformation experiments of Griffith differ from those of Avery and his associates? (b) What was the significant contribution of each? (c) Why was Griffith’s work not evidence for DNA as the genetic material, whereas the experiments of Avery and coworkers provided direct proof that DNA carried the genetic information? ANS: (a) Griffith’s in vivo experiments demonstrated the occurrence of transformation in pneumococcus. They provided no indication as to the molecular basis of the transformation phenomenon. Avery and colleagues carried out in vitro experiments, employing biochemical analyses to demonstrate that transformation was mediated by DNA. (b) Griffith showed that a transforming substance existed; Avery et al. defined it as DNA. (c) Griffith’s experiments did not include any attempt to characterize the substance responsible for transformation. Avery et al . isolated DNA in “pure” form and demonstrated that it could mediate transformation. Feedback: 9.1 Difficulty: easy 9.2 A cell-free extract is prepared from Type IIIS pneumococcal cells. What effect will treatment of this extract with (a) protease, (b) RNase, and (c) DNase have on its subsequent capacity to transform recipient Type IIR cells to Type IIIS? Why? ANS: (a) no effect; (b) no effect; (c) DNase will destroy the capacity of the extract to transform type IIR cells to Type IIIS by degrading the DNA in the extract. Protease and RNase will degrade the proteins and RNA, respectively, in the extract. They will have no effect, since the proteins and RNA are not involved in transformation. Feedback: 9.1 Difficulty: easy 9.3 How could it be demonstrated that the mixing of heat-killed Type III
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pneumococcus with live Type II resulted in a transfer of genetic material from Type III to Type II rather than a restoration of viability to Type III by Type II? ANS: Purified DNA from Type III cells was shown to be sufficient to transform Type II cells. This occurred in the absence of any dead Type III cells. Feedback: 9.1 Difficulty: medium 9.4 What is the macromolecular composition of a bacterial virus or bacteriophage such as phage T2? ANS: About ½ protein, ½ DNA. A single long molecule of DNA is enclosed within a complex “coat” composed of many proteins. Feedback: 9.1 Difficulty: easy 9.5 (a) What was the objective of the experiment carried out by Hershey and Chase? (b) How was the objective accomplished? (c) What is the significance of this experiment? ANS: (a) The objective was to determine whether the genetic material was DNA or protein. (b) By labeling phosphorus, a constituent of DNA, and sulfur, a constituent of protein, in a virus, it was possible to demonstrate that only the labeled phosphorus was introduced into the host cell during the viral reproductive cycle. The DNA was enough to produce new phages. (c)
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This note was uploaded on 11/26/2011 for the course BIOLOGY 2c03 taught by Professor Dej during the Spring '11 term at McMaster University.

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Ch09 - Chapter 9 9.1(a How did the transformation experiments of Griffith differ from those of Avery and his associates(b What was the significant

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