Ch. 10 - DNA Structure and Analysis
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- In this chapter, we first focused on the information that showed DNA to be the genetic material and then discussed the structure of DNA as proposed by Watson and Crick. We concluded the chapter by describing various techniques developed to study DNA. Along the way, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, what answers would you propose to the following fundamental questions: How were scientists able to determine that DNA, and not some other molecule, serves as the genetic material in bacteria and bacteriophages?
Problem 1
- In this chapter, we first focused on the information that showed DNA to be the genetic material and then discussed the structure of DNA as proposed by Watson and Crick. We concluded the chapter by describing various techniques developed to study DNA. Along the way, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, what answers would you propose to the following fundamental questions: How do we know that DNA also serves as the genetic material in eukaryotes such as humans?
Problem 1
- How was it determined that the structure of DNA is a double helix with the two strands held together by hydrogen bonds formed between complementary nitrogenous bases?
Problem 1
- How do we know that G pairs with C and that A pairs with T as complementary base pairs are formed?
Problem 1
- Most center around DNA and RNA and their role of serving as the genetic material. Write a short essay that contrasts these molecules, including a comparison of advantages conferred by their structure that each of them has over the other in serving in this role.
Problem 2
- Discuss the reasons proteins were generally favored over DNA as the genetic material before 1940. What was the role of the tetranucleotide hypothesis in this controversy?
Problem 3
- Contrast the contributions made to an understanding of transformation by Griffith and by Avery and his colleagues.
Problem 4
- Given the state of knowledge at the time of the Avery, MacLeod, and McCarty experiment, why was it difficult for some scientists to accept that DNA is the carrier of genetic information?
Problem 5
- When Avery and his colleagues had obtained what was concluded to be the transforming factor from the IIIS virulent cells, they treated the fraction with proteases, RNase, and DNase, followed in each case by the assay for retention or loss of transforming ability. What were the purpose and results of these experiments? What conclusions were drawn?
Problem 5
- Why were ³²P and ³⁵S chosen for use in the Hershey–Chase experiment? Discuss the rationale and conclusions of this experiment.
Problem 6
- Does the design of the Hershey–Chase experiment distinguish between DNA and RNA as the molecule serving as the genetic material? Why or why not?
Problem 7
- What observations are consistent with the conclusion that DNA serves as the genetic material in eukaryotes? List and discuss them.
Problem 8
- What are the exceptions to the general rule that DNA is the genetic material in all organisms? What evidence supports these exceptions?
Problem 9
- Draw the chemical structure of the three components of a nucleotide, and then link the three together. What atoms are removed from the structures when the linkages are formed?
Problem 10
- How are the carbon and nitrogen atoms of the sugars, purines, and pyrimidines numbered?
Problem 11
- Adenine may also be named 6-amino purine. How would you name the other four nitrogenous bases, using this alternative system? (O is indicated by 'oxy-,' and CH₃ by 'methyl.')
Problem 12
- Human adult hemoglobin is a tetramer containing two alpha (α) and two beta (β) polypeptide chains. The α gene cluster on chromosome 16 and the β gene cluster on chromosome 11 share amino acid similarities such that 61 of the amino acids of the α-globin polypeptide (141 amino acids long) are shared in identical sequence with the β-globin polypeptide (146 amino acids long). How might one explain the existence of two polypeptides with partially shared function and structure on two different chromosomes?
Problem 12
- Draw the chemical structure of a dinucleotide composed of A and G. Opposite this structure, draw the dinucleotide composed of T and C in an antiparallel (or upside-down) fashion. Form the possible hydrogen bonds.
Problem 13
- Describe the various characteristics of the Watson–Crick double-helix model for DNA.
Problem 14
- What evidence did Watson and Crick have at their disposal in 1953? What was their approach in arriving at the structure of DNA?
Problem 15
- What might Watson and Crick have concluded had Chargaff's data from a single source indicated the following? A T G C % 29 19 21 31 Why would this conclusion be contradictory to Wilkins's and Franklin's data?
Problem 16
- How do covalent bonds differ from hydrogen bonds? Define base complementarity.
Problem 17
- List three main differences between DNA and RNA.
Problem 18
- What are the three major types of RNA molecules? How is each related to the concept of information flow?
Problem 19
- How is the absorption of ultraviolet light by DNA and RNA important in the analysis of nucleic acids?
Problem 20
- What is the physical state of DNA after it is heated and denatured?
Problem 21
- What is the hyperchromic effect? How is it measured? What does Tₘ imply?
Problem 22
- Why is Tₘ related to base composition?
Problem 23
- What is the chemical basis of molecular hybridization?
Problem 24
- What did the Watson–Crick model suggest about the replication of DNA?
Problem 25
