Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

8. DNA Replication

Overview of DNA Replication

Genetics

8. DNA Replication

Overview of DNA Replication

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2:41 minutes

Problem 13

Textbook Question

A sample of double-stranded DNA is found to contain 20% cytosine. Determine the percentage of the three other DNA nucleotides in the sample.

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 equals the percentage of guanine in the DNA sample.

Since the DNA is double-stranded, the total percentage of all four nucleotides (C, G, A, T) must add up to 100%.

Given that cytosine (C) makes up 20% of the DNA, guanine (G) must also make up 20% because of the base-pairing rule. Together, cytosine and guanine account for 40% of the DNA.

Subtract the combined percentage of cytosine and guanine (40%) from 100% to determine the combined percentage of adenine (A) and thymine (T).

Divide the remaining percentage equally between adenine (A) and thymine (T), as they pair with each other in equal amounts in double-stranded DNA.

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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 cytosine (C) pairs with guanine (G). This means that the amount of adenine will equal the amount of thymine, and the amount of cytosine will equal the amount of guanine in a double-stranded DNA molecule. Understanding these rules is essential for calculating the percentages of the nucleotides based on the given information.

Complementary Base Pairing

Complementary base pairing refers to the specific pairing of nitrogenous bases in DNA. Since the sample contains 20% cytosine, it must also contain 20% guanine due to their complementary relationship. This concept is crucial for determining the percentages of the other nucleotides in the DNA sample.

Percentage Composition of DNA

The percentage composition of DNA nucleotides can be calculated by knowing the total percentage must equal 100%. Given that cytosine and guanine each account for 20%, the remaining percentage (60%) must be divided equally between adenine and thymine, leading to each being 30%. This concept is fundamental for solving the problem presented.

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