Life: The Science of Biology
Life: The Science of Biology
11th Edition
ISBN: 9781319010164
Author: David E. Sadava, David M. Hillis, H. Craig Heller, Sally D. Hacker
Publisher: W. H. Freeman
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Chapter 13, Problem 1Q
Summary Introduction

To analyze:

The time taken by the DNA polymerase to complete the replication process of the entire DNA molecule of the shortest chromosome, by moving uninterruptedly from one end to the other end. Also figure out whether DNA replication involves one starting point or follows an alternate hypothesis.

Given:

The DNA polymerase proceeds uninterruptedly on the DNA strand, from one end to the other end to synthesize the new DNA strand. Addition of nucleotides on the new DNA strand occurs at the rate of 50 base pairs per second (bp/s). The replication is limited to the S or the synthesis phase of the cell cycle. The shortest chromosome is 21st chromosome in humans and its length is 50×106 bps.

Introduction:

The division of cells in a cell cycle involves two phases: interphase and mitotic phase. Replication of the genetic material takes place during synthesis phase or S phase of the interphase. DNA polymerase is responsible for DNA replication in both eukaryotes and prokaryotes.

Expert Solution & Answer
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Explanation of Solution

The rate at which DNA polymerase proceeds the formation of new DNA strand is 50 bp/s. Therefore, to replicate a DNA strand of 50×106 bps, the enzyme DNA polymerase will take 106 seconds, which is approximately 278 hours.

The synthesis phase of a mammalian cell is 8 hours long, and the entire replication process occurs during this time. This indicates that there must be multiple DNA polymerase complexes involved in this process. Hence more than one replication origin sites must be there, where the enzyme would attach itself to synthesize a new strand.

Conclusion

Therefore, it can be concluded that there are many replication origin sites where DNA polymerase enzyme work simultaneously, to complete the synthesis of new DNA strand.

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Below is a diagram of DNA replication as currently believed to occur in E. coli. Arrows start from numbers and end at specific points. Answer the questions relating to the locations specified by the numbers (1) Which end (5' or 3') of the molecule is here?   (2) Which enzyme is probably functioning here to deal with supercoils in the DNA?   (3) Which enzyme is probably functioning here to unwind the DNA?
Below is a diagram of DNA replication as currently believed to occur in E. coli. From specific points, arrows are provided that lead to numbers.   Answer the questions below relating to the locations specified by the numbers.                                                                              (02)  What end (5’ or 3’) of the molecule is here? (State which) What enzyme is probably functioning here to deal with supercoils in the DNA? What enzyme is probably functioning here to unwind the DNA? What nucleic acid is probably depicted here? What are these short DNA fragments usually called? What enzyme probably functions here to couple these two newly synthesized fragments of DNA? Is this strand the leading or lagging strand? What end (5’ or 3’) of the molecule is here? (State which)
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