Ch.17 Nucleic Acids and Protein Synthesis

Timberlake - Chemistry: An Introduction to General, Organic, and Biological Chemistry 14th Edition

Timberlake14th EditionChemistry: An Introduction to General, Organic, and Biological ChemistryISBN: 9781292472249Not the one you use?Change textbook

Timberlake 14th Edition

Ch.17 Nucleic Acids and Protein Synthesis

Problem 103

Chapter 17, Problem 103

If the DNA double helix in salmon contains 28% adenine, what is the percentage of thymine, guanine, and cytosine?

Verified step by step guidance

Understand the base pairing rules in DNA: Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C). This means the percentage of adenine is equal to the percentage of thymine, and the percentage of guanine is equal to the percentage of cytosine.

Since adenine makes up 28% of the DNA, thymine must also make up 28% due to the base pairing rule.

The total percentage of adenine and thymine combined is 28% + 28% = 56%.

The remaining percentage of the DNA is composed of guanine and cytosine. Subtract the combined percentage of adenine and thymine from 100%: 100% - 56% = 44%.

Divide the remaining percentage equally between guanine and cytosine, as they pair together and are present in equal amounts: 44% ÷ 2 = 22% for guanine and 22% for cytosine.

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Key Concepts

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

Base Pairing Rules

In DNA, the base pairing rules dictate that adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). This means that the amount of adenine in a DNA molecule is always equal to the amount of thymine, while the amount of guanine equals the amount of cytosine. Understanding these rules is essential for calculating the percentages of the other bases when one is known.

Percentage Composition of DNA Bases

The percentage composition of DNA bases refers to the relative amounts of adenine, thymine, guanine, and cytosine in a DNA molecule. In a double-stranded DNA molecule, the total percentage of A and T combined will equal the total percentage of G and C combined. This concept is crucial for solving problems related to the composition of DNA when given partial information.

Complementary Base Pairing

Complementary base pairing is the principle that explains how the bases in DNA strands align with each other. Since adenine pairs with thymine and guanine pairs with cytosine, knowing the percentage of one base allows for the deduction of its complementary base's percentage. This concept is fundamental in determining the overall base composition of DNA when only a subset of data is provided.