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BIOS 105 Chapter 15
- Who performed classic experiments that supported the semiconservative model of DNA
replication?:
Answer Meselson and Stahl
2. What separates the DNA strands during replication?:
Answer Helicase
3. A new DNA strand elongates only in the 5' to 3' direction because:
Answer DNA polymerase can only add nucleotides to the free 3' end.
- What is the role of DNA ligase in the elongation of the lagging strand during DNA
replication?:
Answer It joins Okazaki fragments together
- In humans, xeroderma pigmentosum (XP) is a disorder of the nucleotide excision repair
- methylation of purines
- thymine dimers
- telomere shortening
mechanism. These individuals are unable to repair DNA dam- age caused by ultraviolet light.Which of the following are the most prominent types of DNA lesions in individuals suffering from xeroderma pigmentosum?
D) mismatch errors:
Answer B) thymine dimers
- For a science fair project, two students decided to repeat the Hershey and Chase
experiment, with modifications. They decided to label the nitrogen of the DNA, rather than the phosphate. They reasoned that each nucleotide has only one phosphate and two to five nitrogens. Thus, labeling the nitrogens would provide a stronger signal than labeling the
phosphates. Why won't this experiment work?:
Answer Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins
7. Semiconservative replication involves a template. What is the template?:
Answer one strand of the DNA molecule 1 / 2
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- Use Figure 16.1 to answer the following question.
In the late 1950s, Meselson and Stahl grew bacteria in a medium containing "heavy" nitrogen (15N) and then transferred them to a medium containing 14N. Which of the results in Figure 16.1
would be expected after one round of DNA replication in the presence of 14N?:
Answer 14N-15N hybrid DNA
- In an analysis of the nucleotide composition of DNA, which of the following will be found?:
Answer A + C = G + T
10. The leading and the lagging strands differ in that .:
Answer the leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction
11. DNA is synthesized through a process known as .:
Answer semiconserv- ative replication
- In trying to determine whether DNA or protein is the genetic material, Hershey and
- DNA contains nitrogen, whereas protein does not.
- RNA includes ribose, whereas DNA includes deoxyribose sugars.
- DNA contains purines, whereas protein includes pyrimidines.
- DNA contains phosphorus, whereas protein does not.
Chase made use of which of the following facts?
E) DNA contains sulfur, whereas protein does not.:
Answer D) DNA contains phospho- rus, whereas protein does not
13. What helps to hold the DNA strands apart while they are being replicated?:
Answer single-strand binding proteins
- Which enzyme catalyzes the elongation of a DNA strand in the 5' --> 3' direction?:
Answer DNA polymerase III
15. What is the function of DNA polymerase III?:
Answer to add nucleotides to the end of a growing DNA strand
16. What is the function of topoisomerase?:
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