Multiple Choice
Which of the following is not a component of a nucleotide?
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7. DNA and Chromosome Structure
DNA Structure
2: minutesProblem 1c
Textbook Question
How was it determined that the structure of DNA is a double helix with the two strands held together by hydrogen bonds formed between complementary nitrogenous bases?
Verified step by step guidance1
Understand the historical context: Scientists in the early 20th century knew DNA was the genetic material, but its structure was unknown. Key contributions came from multiple researchers, including Rosalind Franklin, James Watson, Francis Crick, and Maurice Wilkins.
Examine Rosalind Franklin's X-ray diffraction data: Franklin used X-ray crystallography to study the structure of DNA. Her famous 'Photo 51' revealed an X-shaped diffraction pattern, indicating a helical structure with repeating patterns.
Incorporate Chargaff's rules: Erwin Chargaff discovered that the amount of adenine (A) in DNA equals the amount of thymine (T), and the amount of cytosine (C) equals the amount of guanine (G). This suggested base pairing between A-T and C-G.
Analyze Watson and Crick's model-building approach: Using Franklin's data and Chargaff's rules, Watson and Crick proposed a double-helix model where two strands of DNA run in opposite directions (antiparallel) and are held together by hydrogen bonds between complementary bases (A-T with 2 hydrogen bonds, C-G with 3 hydrogen bonds).
Verify the model through experimental evidence: The double-helix model explained how DNA could replicate and store genetic information. Subsequent experiments confirmed the model's accuracy, solidifying the understanding of DNA's structure.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Double Helix Structure
The double helix is the three-dimensional shape of DNA, resembling a twisted ladder. This structure consists of two long strands of nucleotides that run in opposite directions, with the sugar-phosphate backbone on the outside and the nitrogenous bases on the inside. The helical shape is crucial for DNA's stability and function, allowing it to store genetic information efficiently.
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Complementary Base Pairing
Complementary base pairing refers to the specific pairing of nitrogenous bases in DNA: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). This pairing is essential for the accurate replication of DNA and the transmission of genetic information. The hydrogen bonds formed between these pairs stabilize the double helix structure.
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Hydrogen Bonds
Hydrogen bonds are weak interactions that occur between the hydrogen atom of one molecule and an electronegative atom of another, such as oxygen or nitrogen. In DNA, these bonds form between the nitrogenous bases of the two strands, providing the necessary stability to hold the strands together while allowing them to separate during processes like replication and transcription.
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