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Ch. 9 - DNA Structure and Analysis
Klug - Essentials of Genetics 10th Edition
Klug10th EditionEssentials of GeneticsISBN: 9780135588789당신이 사용하는 게 아니라요?교과서 변경
9장, 문제 28

One of the most common spontaneous lesions that occurs in DNA under physiological conditions is the hydrolysis of the amino group of cytosine, converting the cytosine to uracil. What would be the effect on DNA structure of a uracil group replacing cytosine?

검증된 단계별 안내
1
Understand that cytosine normally pairs with guanine in DNA through three hydrogen bonds, maintaining the DNA double helix structure.
Recognize that when cytosine undergoes deamination, it is converted into uracil, which is not a normal base in DNA but is normally found in RNA.
Consider that uracil pairs preferentially with adenine through two hydrogen bonds, unlike cytosine which pairs with guanine.
Analyze how the presence of uracil in DNA would lead to a mismatch during DNA replication, potentially causing a C-G to T-A transition mutation if not repaired.
Conclude that the incorporation of uracil disrupts the normal base pairing and can lead to mutations, which is why cells have repair mechanisms like uracil-DNA glycosylase to remove uracil from DNA.

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주요 개념

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Spontaneous DNA Lesions and Deamination

Spontaneous DNA lesions are natural chemical changes that occur without external influence. Deamination is the removal of an amino group from a base, such as cytosine converting to uracil, which alters the base's identity and can lead to mutations if unrepaired.
추천 영상:
가이드 코스
09:52
Spontaneous Mutations

Base Pairing and DNA Structure

DNA structure relies on specific base pairing: cytosine pairs with guanine via three hydrogen bonds. Replacing cytosine with uracil disrupts this pairing because uracil pairs with adenine, potentially causing mismatches and destabilizing the double helix.
추천 영상:

DNA Repair Mechanisms for Uracil

Cells have repair systems like base excision repair to recognize and remove uracil in DNA, preventing mutations. Uracil-DNA glycosylase excises uracil bases, maintaining DNA integrity by restoring correct cytosine-guanine pairs.
추천 영상:
가이드 코스
05:44
Repair Pathways
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교과서 질문

A primitive eukaryote was discovered that displayed a unique nucleic acid as its genetic material. Analysis provided the following information:

A major hyperchromic shift is evident upon heating and monitoring UV absorption at 260 nm.

437
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교과서 질문

A primitive eukaryote was discovered that displayed a unique nucleic acid as its genetic material. Analysis provided the following information:

About 75 percent of the sugars are deoxyribose, while 25 percent are ribose.

Postulate a model for the structure of this molecule that is consistent with the foregoing observations.

406
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교과서 질문

A primitive eukaryote was discovered that displayed a unique nucleic acid as its genetic material. Analysis provided the following information:

Base-composition analysis reveals four bases in the following proportions: Adenine = 8%; Guanine = 37%; Xanthine = 37%; Hypoxanthine = 18%

412
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교과서 질문

Newsdate: March 1, 2030. A unique creature has been discovered during exploration of outer space. Recently, its genetic material has been isolated and analyzed. This material is similar in some ways to DNA in its chemical makeup. It contains in abundance the 4-carbon sugar erythrose and a molar equivalent of phosphate groups. In addition, it contains six nitrogenous bases: adenine (A), guanine (G), thymine (T), cytosine (C), hypoxanthine (H), and xanthine (X). These bases exist in the following relative proportions:

A =T = H and C = G = X

X-ray diffraction studies have established a regularity in the molecule and a constant diameter of about 30 Å. Together, these data have suggested a model for the structure of this molecule.

Propose a general model of this molecule. Describe it briefly.

541
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교과서 질문

In some organisms, cytosine is methylated at carbon 5 of the pyrimidine ring after it is incorporated into DNA. If a 5-methyl cytosine molecule is then hydrolyzed, what base will be generated?

643
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교과서 질문

Newsdate: March 1, 2030. A unique creature has been discovered during exploration of outer space. Recently, its genetic material has been isolated and analyzed. This material is similar in some ways to DNA in its chemical makeup. It contains in abundance the 4-carbon sugar erythrose and a molar equivalent of phosphate groups. In addition, it contains six nitrogenous bases: adenine (A), guanine (G), thymine (T), cytosine (C), hypoxanthine (H), and xanthine (X). These bases exist in the following relative proportions:

A =T = H and C = G = X

X-ray diffraction studies have established a regularity in the molecule and a constant diameter of about 30 Å. Together, these data have suggested a model for the structure of this molecule.

What base-pairing properties must exist for H and for X in the model?

532
views