Ch. 7 - DNA Structure and Replication

Sanders - Genetic Analysis: An Integrated Approach 3rd Edition

Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook

Sanders 3rd Edition

Ch. 7 - DNA Structure and Replication

Problem 35b

Chapter 7, Problem 35b

You are participating in a study group preparing for an upcoming genetics exam, and one member of the group proposes that each of you draw the structure of two DNA nucleotides joined in a single strand. The figures are drawn and exchanged for correction. You receive the accompanying diagram to correct: What is wrong with the way the nucleotides are joined?

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Examine the structure of the two DNA nucleotides in the diagram. Recall that a nucleotide consists of three components: a phosphate group, a deoxyribose sugar, and a nitrogenous base.

Check the connection between the two nucleotides. In a DNA strand, nucleotides are joined by a phosphodiester bond, which forms between the 3' hydroxyl (-OH) group of the sugar in one nucleotide and the 5' phosphate group of the sugar in the next nucleotide.

Verify if the 3' hydroxyl group of the first nucleotide is correctly linked to the 5' phosphate group of the second nucleotide. If the bond is missing or incorrectly formed, this is an error.

Ensure that the orientation of the sugar-phosphate backbone is correct. The backbone should have a 5' to 3' directionality, meaning the first nucleotide's 5' end is free, and the last nucleotide's 3' end is free.

Check for any additional errors, such as mismatched or missing components (e.g., a missing phosphate group, incorrect sugar structure, or nitrogenous base not attached to the correct carbon of the sugar).

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Key Concepts

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

DNA Nucleotide Structure

A DNA nucleotide consists of three components: a phosphate group, a deoxyribose sugar, and a nitrogenous base. The phosphate group connects to the 5' carbon of the sugar, while the nitrogenous base attaches to the 1' carbon. Understanding this structure is crucial for recognizing how nucleotides link together to form DNA strands.

Phosphodiester Bond

Nucleotides in a DNA strand are joined by phosphodiester bonds, which form between the phosphate group of one nucleotide and the hydroxyl group on the 3' carbon of the sugar of another nucleotide. This bond creates a sugar-phosphate backbone, essential for the stability and integrity of the DNA structure.

Antiparallel Orientation

DNA strands have an antiparallel orientation, meaning that one strand runs in the 5' to 3' direction while the complementary strand runs in the 3' to 5' direction. This orientation is critical for the proper pairing of nitrogenous bases and for the functioning of enzymes during DNA replication and transcription.

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Related Practice

Textbook Question

What would be the effects on DNA replication if mutation of DNA pol III caused it to lose each of the following activities?

3′ to 5′ exonuclease activity

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Textbook Question

A sufficient amount of a small DNA fragment is available for dideoxy sequencing. The fragment to be sequenced contains 20 nucleotides following the site of primer binding: 5'-ATCGCTCGACAGTGACTAGC-[primer site]-3' Dideoxy sequencing is carried out, and the products of the four sequencing reactions are separated by gel electrophoresis. Draw the bands you expect will appear on the gel from each of the sequencing reactions.

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Textbook Question

You are participating in a study group preparing for an upcoming genetics exam, and one member of the group proposes that each of you draw the structure of two DNA nucleotides joined in a single strand. The figures are drawn and exchanged for correction. You receive the accompanying diagram to correct: Identify and correct at least five things that are wrong in the depiction of each nucleotide.

Suppose that future exploration of polar ice on Mars identifies a living microbe and that analysis indicates the organism carries double-stranded DNA as its genetic material. Suppose further that DNA replication analysis is performed by first growing the microbe in a growth medium containing the heavy isotope of nitrogen (¹⁴N) that the organism is then transferred to a growth medium containing the light isotope of nitrogen (¹⁴N) and that the nitrogen composition of the DNA is examined by CsCl ultracentrifugation and densitometry after the first, second, and third replication cycles in the ¹⁴N-containing medium. The results of the experiment are illustrated here for each cycle. The control shows the positioning of the three possible DNA densities. Based on the results shown, what can you conclude about the mechanism of DNA replication in this organism?

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Textbook Question

The following diagram shows the parental strands of a DNA molecule undergoing replication.

Draw the daughter strands present in the replication bubble, indicating:

a. The polarity of daughter strands

b. The leading and lagging strands

c. Okazaki fragments

d. The locations of RNA primers

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