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Ch. 11 - DNA Replication and Recombination
All textbooksKlug 12th EditionCh. 11 - DNA Replication and RecombinationProblem 28
Chapter 11, Problem 28

Assume that the sequence of bases shown below is present on one nucleotide chain of a DNA duplex and that the chain has opened up at a replication fork. Synthesis of an RNA primer occurs on this template starting at the base that is underlined. If the RNA primer consists of eight nucleotides, what is its base sequence?

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1
Identify the DNA sequence provided and locate the underlined base where the RNA primer synthesis starts.
Determine the direction of synthesis for the RNA primer, which is 5' to 3'.
Identify the complementary RNA bases for the DNA template starting from the underlined base. Remember that in RNA, adenine (A) pairs with uracil (U), thymine (T) pairs with adenine (A), cytosine (C) pairs with guanine (G), and guanine (G) pairs with cytosine (C).
Write down the sequence of the RNA primer by selecting the first eight nucleotides that are complementary to the DNA template starting from the underlined base.
Ensure that the RNA primer sequence is written in the 5' to 3' direction.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

DNA Structure

DNA is composed of two strands forming a double helix, with each strand made up of nucleotides. Each nucleotide consists of a phosphate group, a sugar, and a nitrogenous base (adenine, thymine, cytosine, or guanine). The sequence of these bases encodes genetic information, and during replication, the strands separate to allow for the synthesis of new complementary strands.
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RNA Primer Synthesis

During DNA replication, an RNA primer is synthesized by the enzyme primase. This primer is essential for DNA polymerase to initiate DNA synthesis, as it provides a free 3' hydroxyl group for the addition of DNA nucleotides. The RNA primer is complementary to the DNA template strand and is typically shorter than the DNA strands being synthesized.
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Base Pairing Rules

Base pairing rules dictate how nucleotides pair in DNA and RNA. In DNA, adenine pairs with thymine (A-T) and cytosine pairs with guanine (C-G). In RNA, uracil replaces thymine, pairing with adenine (A-U). Understanding these rules is crucial for determining the sequence of the RNA primer based on the DNA template strand.
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Related Practice
Textbook Question
At the end of the short arm of human chromosome 16 (16p), several genes associated with disease are present, including thalassemia and polycystic kidney disease. When that region of chromosome 16 was sequenced, gene-coding regions were found to be very close to the telomere-associated sequences. Could there be a possible link between the location of these genes and the presence of the telomere-associated sequences? What further information concerning the disease genes would be useful in your analysis?
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Textbook Question
DNA polymerases in all organisms add only 5' nucleotides to the 3' end of a growing DNA strand, never to the 5' end. One possible reason for this is the fact that most DNA polymerases have a proofreading function that would not be energetically possible if DNA synthesis occurred in the 3' to 5' direction. Sketch the reaction that DNA polymerase would have to catalyze if DNA synthesis occurred in the 3' to 5' direction.
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Textbook Question
DNA polymerases in all organisms add only 5' nucleotides to the 3' end of a growing DNA strand, never to the 5' end. One possible reason for this is the fact that most DNA polymerases have a proofreading function that would not be energetically possible if DNA synthesis occurred in the 3' to 5' direction. Consider the information in your sketch and speculate as to why proofreading would be problematic.
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Textbook Question
Assume that the sequence of bases shown below is present on one nucleotide chain of a DNA duplex and that the chain has opened up at a replication fork. Synthesis of an RNA primer occurs on this template starting at the base that is underlined. In the intact RNA primer, which nucleotide has a free 3'-OH terminus? 3'.......GGCTACCTGGATTCA....5'
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Textbook Question
Reiji and Tuneko Okazaki conducted a now classic experiment in 1968 in which they discovered a population of short fragments synthesized during DNA replication. They introduced a short pulse of ³H-thymidine into a culture of E. coli and extracted DNA from the cells at various intervals. In analyzing the DNA after centrifugation in denaturing gradients, they noticed that as the interval between the time of ³H-thymidine introduction and the time of centrifugation increased, the proportion of short strands decreased and more labeled DNA was found in larger strands. What would account for this observation?
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