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Chapter 18: Problem 7

How do alkylating agents, nitrous acid, and hydroxylamine produce mutations?

Short Answer

Expert verified
Alkylating agents add alkyl groups to DNA; nitrous acid deaminates bases; hydroxylamine modifies cytosine to pair with adenine, all causing mutations.

Step by step solution

01

Understanding Alkylating Agents

Alkylating agents produce mutations by adding alkyl groups to the DNA molecule. This process can cause the formation of cross-links between the DNA strands or the distortion of the DNA helix, leading to base mispairing during DNA replication. The result is that incorrect bases may be incorporated into the DNA sequence, causing mutations.
02

The Effect of Nitrous Acid

Nitrous acid induces mutations by deaminating bases in DNA. Specifically, it converts cytosine to uracil and adenine to hypoxanthine. These conversions lead to mispairing of bases during DNA replication. For example, uracil pairs with adenine instead of guanine, and hypoxanthine pairs with cytosine instead of thymine, leading to mutations.
03

Understanding Hydroxylamine's Mechanism

Hydroxylamine specifically acts on cytosine bases, converting them to hydroxylaminocytosine. This modified base pairs with adenine instead of guanine during DNA replication. As a result, C-G (cytosine-guanine) pairs are converted to T-A (thymine-adenine), thereby generating mutations in the DNA sequence.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Alkylating Agents
Alkylating agents are a class of chemicals capable of transferring alkyl groups to DNA molecules. This process leads to mutations that can disrupt normal cellular function. These agents interact with DNA by attaching alkyl groups, often to the nitrogen atom of a nucleotide base. This can alter the structural integrity of DNA in several ways.
  • They can create cross-links between strands of DNA, making it difficult for the DNA to unwind and replicate.
  • An alkylated base might mispair during replication. For instance, a guanine alkylated by an alkylating agent might pair incorrectly with thymine.

These structural changes can lead to errors when the cell replicates its DNA, potentially causing a variety of mutations. Alkylating agents are used in chemotherapy due to their ability to hinder rapidly dividing cancer cells, but they can also introduce mutations that may lead to secondary cancers.
Nitrous Acid
Nitrous acid is a potent mutagen that works through a process called deamination. Deamination is the removal of an amino group from a molecule, and when applied to DNA, it can change the base's identity.
  • When cytosine is deaminated by nitrous acid, it becomes uracil, which can pair incorrectly during DNA replication.
  • Adenine, when deaminated, becomes hypoxanthine, leading to yet another mismatch when paired.

These changes in base pairing can cause the introduction of errors into newly synthesized DNA strands because the modified bases partner incorrectly. For example, uracil will pair with adenine instead of the intended guanine, causing a mutation during cellular replication. These mutations can affect protein synthesis and function extensively if not corrected by DNA repair mechanisms.
Hydroxylamine
Hydroxylamine is a chemical that specifically reacts with cytosine bases in DNA, converting them into hydroxylaminocytosine. This modification distorts the base pairing rules.
  • Hydroxylaminocytosine will mispair with adenine during DNA replication instead of its usual partner, guanine.
  • This swapping leads from a C-G pair to a T-A pair, effectively inducing a mutation.

These conversions can significantly affect the evolutionary properties of an organism's genome by introducing errors that, if left unrepaired, persist through generations of cellular division. While hydroxylamine itself is not used directly in medical treatments, understanding its mechanisms provides insight into mutation processes and the ways environmental agents can alter DNA.

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Most popular questions from this chapter

In many eukaryotic organisms, a significant proportion of cytosine bases are naturally methylated to 5 -methylcytosine. Through evolutionary time, the proportion of AT base pairs in the DNA of these organisms increases. Can you suggest a possible mechanism for this increase?

What are the two major mechanisms for the repair of double-strand breaks? How do they differ?

White eyes in Drosophila melanogaster result from an X-linked recessive mutation. Occasionally, white-eyed mutants give rise to offspring that possess white eyes with small red spots. The number, distribution, and size of the red spots are variable. Explain how a transposable element could be responsible for this spotting phenomenon.

Draw the structure of a typical insertion sequence and identify its parts.

What general characteristics are found in many transposable elements?
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