Ch.11 Nucleic Acids Big Molecules with a Big Role

Frost - General, Organic and Biological Chemistry 4th Edition

Frost4th EditionGeneral, Organic and Biological ChemistryISBN: 9780134988696Not the one you use?Change textbook

Frost 4th Edition

Ch.11 Nucleic Acids Big Molecules with a Big Role

Problem 86b

Chapter 7, Problem 86b

If the DNA chromosomes of humans contain 20% cytosine, what is the percent of guanine, adenine, and thymine?

Verified step by step guidance

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

Since cytosine makes up 20% of the DNA, guanine must also make up 20% of the DNA. This is due to the complementary base pairing rule.

The total percentage of cytosine and guanine combined is 20% + 20% = 40%. This leaves 60% of the DNA to be composed of adenine and thymine.

Divide the remaining 60% equally between adenine and thymine, as they are complementary pairs. This means adenine makes up 30% and thymine makes up 30%.

Summarize the percentages: Cytosine = 20%, Guanine = 20%, Adenine = 30%, Thymine = 30%. These percentages should add up to 100%.

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Key Concepts

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

Chargaff's Rules

Chargaff's Rules state that in DNA, the amount of adenine (A) is equal to thymine (T), and the amount of cytosine (C) is equal to guanine (G). This means that if you know the percentage of one base, you can determine the percentage of its complementary base. For example, if cytosine is 20%, then guanine must also be 20%.

Base Pairing in DNA

Base pairing in DNA refers to the specific pairing of nitrogenous bases: adenine pairs with thymine, and cytosine pairs with guanine. This complementary base pairing is crucial for the structure of the DNA double helix and ensures accurate replication and transcription of genetic information. Understanding this concept 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, cytosine, and guanine in a DNA molecule. Since the total percentage of all four bases must equal 100%, knowing the percentage of one base allows for the calculation of the others. In this case, if cytosine is 20%, then guanine is also 20%, leaving 60% for adenine and thymine combined, which must be equally divided between them.

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Textbook Question

Alpha-melanocyte stimulating hormone (α-MSH) is a 13-amino-acid peptide hormone responsible for pigmentations in hair and skin. Its peptide sequence is shown.

SYSMQHFRWGKPV

a. How many nucleotides would be found in the mRNA for this protein?

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Textbook Question

Alpha-melanocyte stimulating hormone (α-MSH) is a 13-amino-acid peptide hormone responsible for pigmentations in hair and skin. Its peptide sequence is shown.

SYSMQHFRWGKPV

b. Suggest an mRNA sequence for the peptide. Show the 5' and 3' ends.

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Textbook Question

Alpha-melanocyte stimulating hormone (α-MSH) is a 13-amino-acid peptide hormone responsible for pigmentations in hair and skin. Its peptide sequence is shown.

SYSMQHFRWGKPV

c. Suggest a complementary template DNA sequence based on the mRNA sequence suggested in part b.

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Textbook Question

A protein contains 35 amino acids. How many nucleotides would be found in the mRNA code for this protein?

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Textbook Question

The DNA double helix can unwind, or denature, at temperatures between 90 °C and 99 °C. Denaturing occurs when H bonds are broken. Which of the following strands of DNA would be expected to denature at a higher temperature? Provide an explanation.

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