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

7. DNA and Chromosome Structure

DNA Structure

Genetics

7. DNA and Chromosome Structure

DNA Structure

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2:44 minutes

Problem 1

Textbook Question

How do we know that G pairs with C and that A pairs with T as complementary base pairs are formed?

Verified step by step guidance

Understand the structure of DNA: DNA is a double-stranded molecule where the two strands are held together by hydrogen bonds between nitrogenous bases. These bases are adenine (A), thymine (T), guanine (G), and cytosine (C).

Learn about Chargaff's rules: Erwin Chargaff discovered that in DNA, the amount of adenine (A) is equal to the amount of thymine (T), and the amount of guanine (G) is equal to the amount of cytosine (C). This observation suggested specific pairing between these bases.

Examine the hydrogen bonding patterns: A and T form two hydrogen bonds, while G and C form three hydrogen bonds. This specific bonding pattern ensures stability and proper alignment of the DNA double helix.

Consider the molecular shapes: The molecular structures of A, T, G, and C allow them to fit together in a complementary manner. A purine (A or G) always pairs with a pyrimidine (T or C) to maintain a uniform width of the DNA double helix.

Review experimental evidence: X-ray diffraction studies by Rosalind Franklin and the Watson-Crick model of DNA confirmed the complementary base pairing, showing that A pairs with T and G pairs with C to form the stable double-helix structure.

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Key Concepts

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

Complementary Base Pairing

Complementary base pairing refers to the specific pairing of nitrogenous bases in DNA and RNA. In DNA, adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). This pairing is due to hydrogen bonding, where A forms two hydrogen bonds with T, and C forms three hydrogen bonds with G, ensuring the stability and integrity of the DNA double helix.

Chargaff's Rules

Chargaff's rules state that in a given DNA molecule, the amount of adenine equals thymine (A=T) and the amount of cytosine equals guanine (C=G). This observation was crucial in understanding the structure of DNA, as it provided evidence for the complementary nature of base pairing, which is fundamental to DNA replication and transcription processes.

DNA Structure

The structure of DNA is a double helix formed by two strands of nucleotides running in opposite directions. Each nucleotide consists of a sugar, a phosphate group, and a nitrogenous base. The specific arrangement of these bases along the strands, with complementary base pairing, allows for the encoding of genetic information and the faithful transmission of this information during cell division.