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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
All textbooksSanders 3rd EditionCh. 7 - DNA Structure and ReplicationProblem 35c
Chapter 7, Problem 35c

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: Draw this single-stranded segment correctly.

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1
Identify the basic structure of a DNA nucleotide, which consists of three components: a phosphate group, a deoxyribose sugar, and a nitrogenous base (adenine, thymine, cytosine, or guanine).
Understand how two nucleotides are joined in a single strand of DNA: the phosphate group of one nucleotide forms a phosphodiester bond with the 3' hydroxyl group (-OH) of the deoxyribose sugar in the next nucleotide.
Ensure the orientation of the strand is correct: DNA strands have directionality, with a 5' end (phosphate group) and a 3' end (hydroxyl group). Verify that the phosphate group is attached to the 5' carbon of the sugar and the hydroxyl group is on the 3' carbon of the sugar.
Check the nitrogenous bases: confirm that each nucleotide has one nitrogenous base attached to the 1' carbon of the deoxyribose sugar. The bases should not be directly bonded to each other in a single strand.
Redraw the structure if necessary, ensuring the correct sequence of components: phosphate group, deoxyribose sugar, and nitrogenous base, with proper phosphodiester bonds between the nucleotides and the correct 5' to 3' orientation.

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Key Concepts

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

Structure of DNA Nucleotides

DNA nucleotides consist of three components: a phosphate group, a deoxyribose sugar, and a nitrogenous base (adenine, thymine, cytosine, or guanine). The phosphate group and sugar form the backbone of the DNA strand, while the nitrogenous bases extend from the sugar and are responsible for base pairing in double-stranded DNA.
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Single-Stranded DNA

Single-stranded DNA (ssDNA) refers to a form of DNA that consists of only one strand of nucleotides, as opposed to the double helix structure of double-stranded DNA (dsDNA). In ssDNA, the nucleotides are linked together by phosphodiester bonds, and the sequence of bases along the strand encodes genetic information.
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Phosphodiester Bond

A phosphodiester bond is a type of covalent bond that links the phosphate group of one nucleotide to the hydroxyl group on the sugar of another nucleotide. This bond forms the backbone of the DNA strand, allowing for the formation of long chains of nucleotides, which are essential for the structural integrity and function of DNA.
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Related Practice
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.

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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: What is wrong with the way the nucleotides are joined?

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Textbook Question

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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Textbook Question

Go to the OMIM website (https://www.ncbi.nlm.nih.gov/omim) and type 'dyskeratosis congenita autosomal dominant 1' (DKCA1) into the search bar. The result will include a clickable link to the disorder that has an OMIM number of 127550. Review the OMIM information you retrieve and notice that this disorder is caused by a mutation of a telomerase gene that results in abnormally rapid shortening of telomeres and the appearance of disease symptoms at progressively younger ages in successive generations of the affected families. Use this and other information on OMIM to assist with this problem. Go to reference number 15 at the bottom of the OMIM page for a link to a 2004 paper by Tom Vulliamy and colleagues that appeared in the journal Nature Genetics. Click on the 'Full text' option and download a copy of the paper. Look at Table 1 of the paper on page 448. This table lists the lengths of telomeres measured in members of the families in this study. Telomeres shorten with age, and the telomere lengths in Table 1 are age-adjusted. The negative numbers for telomere lengths in the table indicate that telomeres are shorter than average for age, and the more negative the number, the shorter the telomere. Based on Table 1, the discussion in the Vulliamy et al. (2004) paper, and information available on OMIM, answer the following:

How do telomere lengths in children compare with telomere lengths of their parents?

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