Concept explainers
HOW DO WE KNOW?
In this chapter, we focused on how DNA is organized at the chromosomal level. 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:
(a) How do we know that viral and bacterial chromosomes most often consist of circular DNA molecules devoid of protein?
(b) What is the experimental basis for concluding that puffs in polytene chromosomes and loops in lampbrush chromosomes are areas of intense transcription of RNA?
(c) How did we learn that eukaryotic chromatin exists in the form of repeating nucleosomes, each consisting of about 200 base pairs and an octamer of histones?
(d) How do we know that satellite DNA consists of repetitive sequences and has been derived from regions of the centromere?
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ESSENTIALS OF GENETICS-MODIFIED ACCESS
- In the Meselson-Stahl experiment on DNA replication, what fraction of the DNA was composed of one light strand and one heavy strand ("hybrid") after one generation of growth in medium containing 14N? After two generations of growth in a medium containing 14N? What fraction of hybrid DNA is expected after n generations of growth in a medium containing 14N?arrow_forwardWhat are the three models of DNA replication? With the aid of illustrations, show how the Meselson Stahl experiment come to the conclusion of one model of DNA replication. Is DNA replication bidirectional? How did you arrive at this conclusion? Explain the bacterial replication model that supports this conclusion.arrow_forwardIf the bandicoot genome is 3.62 x 109 base pairs, and the "highly repetitive DNA" fraction is composed entirely of copies of sequence 5'TGCGTGTGTGC3' and its complement, how many copies of this sequence are present in the bandicoot genome?arrow_forward
- In terms of new DNA strands that are generated, what are the differences between replication and conventional polymerase chain reactions?arrow_forwardWhy is the replication of DNA referred to as a semiconservative process? What is the experimental evidence for the semiconservative nature of the process? What experimental results would you expect if replication of DNA were a conservative process?arrow_forwardIn terms of the new DNA strands that are generated, what are the differences between replication and conventional polymerase chain reaction?arrow_forward
- Suppose that E. coli synthesizes DNA at a rate of 100,000 nucleotides per minute and takes 40 minutes to replicate its chromosome. (a) How many base pairs are present in the entire E. coli chromosome? (b) What is the physical length of the chromosome in its helical configuration—that is, what is the circumference of the chromosome if it were opened into a circle?arrow_forwardAn article entitled “Nucleosome Positioning at the Replication Fork” states: “both the ‘old’ randomly segregated nucleosomes as well as the ‘new’ assembled histone octamers rapidly position themselves (within seconds) on the newly replicated DNA strands” [Lucchini et al. (2002)]. Given this statement, how would one compare the distribution of nucleosomes and DNA in newly replicated chromatin? How could one experimentally test the distribution of nucleosomes on newly replicated chromosomes?arrow_forwardReferring to Figure 7-20, answer the following questions:a. What is the DNA polymerase I enzyme doing?b. What other proteins are required for the DNApolymerase III on the left to continue synthesizingDNA?c. What other proteins are required for the DNApolymerase III on the right to continue synthesizingDNA?arrow_forward
- On further analysis of the DNA described in conceptual questionC21, you discover that the triplex DNA in this alien organism iscomposed of a double helix with a third strand wound within themajor groove (just like the DNA in Figure shown). How would youpropose that this DNA is able to replicate itself? In your answer,be specific about the base-pairing rules within the double helixand which part of the triplex DNA would be replicated first.arrow_forwardWhen DNA replication was investigated by using heavy, N15 DNA to mark the original molecules, and light, N14 DNA to mark the newly synthesized molecules, one band was found in the middle of the centrifuge column after one round of replication, and two bands were found (middle and top of column) after 2 rounds of replication. Imagine that after 1 round of replication 2 bands were found, one at the bottom and one at the top of the centrifuge column. In that case, what model of DNA replication would have been supported? The dispersive model The conservative model The Franklin model The semi-conservative modelarrow_forwardWhat results would be expected in the experiment outlined in Figure if, during replication, all the original histone proteins remained on one strand of the DNA and new histones attached to the other strand?arrow_forward
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