Multiple Choice
Which of the following best describes a DNA molecule?
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7. DNA and Chromosome Structure
DNA Structure
2:44 minutesProblem 1d
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 guidance1
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.
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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.
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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.
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