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Ch. 1 - The Molecular Basis of Heredity, Variation, and Evolution
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
All textbooksSanders 3rd EditionCh. 1 - The Molecular Basis of Heredity, Variation, and EvolutionProblem 29a
Chapter 1, Problem 29a

Consider the following segment of DNA:
    5'-...ATGCCAGTCACTGACTTG...-3'
    3'-...TACGGTCAGTGACTGAAC...-5'
How many phosphodiester bonds are required to form this segment of double-stranded DNA?

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1
Identify the number of nucleotides in the given DNA sequence. Count the number of bases in one strand (e.g., the 5'-3' strand) since both strands are complementary and will have the same number of nucleotides.
Recall that each nucleotide in a DNA strand is connected to the next nucleotide by a phosphodiester bond. Therefore, the number of phosphodiester bonds in a single strand is equal to the number of nucleotides minus one.
Since the DNA is double-stranded, calculate the total number of phosphodiester bonds by multiplying the number of bonds in one strand by two (as each strand has its own set of phosphodiester bonds).
Note that the phosphodiester bonds are only within each strand and not between the two strands. The two strands are held together by hydrogen bonds between complementary bases, not phosphodiester bonds.
Combine the results to determine the total number of phosphodiester bonds required to form the double-stranded DNA segment.

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Key Concepts

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

Phosphodiester Bonds

Phosphodiester bonds are covalent linkages that connect the 5' phosphate group of one nucleotide to the 3' hydroxyl group of another nucleotide in a DNA strand. These bonds form the backbone of the DNA molecule, providing structural integrity and allowing for the formation of long chains of nucleotides. Each bond is crucial for maintaining the continuity of the DNA strand.
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DNA Structure

Double-Stranded DNA Structure

Double-stranded DNA consists of two complementary strands that run in opposite directions, known as antiparallel orientation. Each strand is made up of nucleotides, which pair specifically (adenine with thymine, and cytosine with guanine) through hydrogen bonds. Understanding this structure is essential for determining how many phosphodiester bonds are present, as each strand contributes to the overall length of the DNA segment.
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Counting Nucleotides

To determine the number of phosphodiester bonds in a DNA segment, one must count the nucleotides in each strand. Each nucleotide, except for the terminal ones, is linked to its neighbor by a phosphodiester bond. Therefore, the total number of bonds is equal to the total number of nucleotides minus one for each strand, as the ends do not form bonds with additional nucleotides.
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Multiple Cross Overs and Interference
Related Practice
Textbook Question

Four nucleic-acid samples are analyzed to determine the percentages of the nucleotides they contain. Survey the data in the table to determine which samples are DNA and which are RNA, and specify whether each sample is double-stranded or single-stranded. Justify each answer.

[A table of nucleotide percentages appears below the problem]

        

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Textbook Question

What is meant by the term homology? How is that different from the meaning of homoplasmy?

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Textbook Question

If one is constructing a phylogeny of reptiles using DNA sequence data, which taxon (birds, mammals, amphibians, or fish) might be suitable to use as an outgroup?

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Textbook Question

Consider the following segment of DNA:

    5'-...ATGCCAGTCACTGACTTG...-3'

    3'-...TACGGTCAGTGACTGAAC...-5'

How many hydrogen bonds are present in this DNA segment?

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Textbook Question

Consider the following segment of DNA:

    5'-...ATGCCAGTCACTGACTTG...-3'

    3'-...TACGGTCAGTGACTGAAC...-5'

If the lower strand of DNA serves as the template transcribed into mRNA, how many peptide bonds are present in the polypeptide fragment into which the mRNA is translated?

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Textbook Question

Ethical and social issues have become a large part of the public discussion of genetics and genetic testing. Choose two of the propositions presented here and prepare a list of arguments for and against them.

The results of genetic testing for susceptibility to cancer, heart disease, and diabetes should be available to insurance companies and current or prospective employers to provide more information for decision-making.

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