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What evidence did Watson and Crick have at their disposal in 1953? What was their approach in arriving at the structure of DNA?
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Ch. 9 - DNA Structure and Analysis
Klug10th EditionEssentials of GeneticsISBN: 9780135588789
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TOC.tableOfContents
- Ch. 1 - Introduction to Genetics16
- Ch. 2 - Mitosis and Meiosis28
- Ch. 3 - Mendelian Genetics37
- Ch. 4 - Modification of Mendelian Ratios53
- Ch. 5 - Sex Determination and Sex Chromosomes32
- Ch. 6 - Chromosome Mutations: Variation in Number and Arrangement37
- Ch. 7 - Linkage and Chromosome Mapping in Eukaryotes36
- Ch. 8 - Genetic Analysis and Mapping in Bacteria and Bacteriophages24
- Ch. 9 - DNA Structure and Analysis38
- Ch. 10 - DNA Replication29
- Ch. 11 - Chromosome Structure and DNA Sequence Organization22
- Ch. 12 - The Genetic Code and Transcription36
- Ch. 13 - Translation and Proteins27
- Ch. 14 - Gene Mutation, DNA Repair, and Transposition34
- Ch. 15 - Regulation of Gene Expression in Bacteria22
- Ch. 16 - Regulation of Gene Expression in Eukaryotes37
- Ch. 17 - Recombinant DNA Technology27
- Ch. 18 - Genomics, Bioinformatics, and Proteomics30
- Ch. 19 - The Genetics of Cancer21
- Ch. 20 - Quantitative Genetics and Multifactorial Traits37
- Ch. 21 - Population and Evolutionary Genetics45
Klug10th EditionEssentials of GeneticsISBN: 9780135588789Non è quello che usi tu?Cambia libro di testo
Capitolo 9, Problema 16
What might Watson and Crick have concluded had Chargaff's data from a single source indicated the following?
Why would this conclusion be contradictory to Wilkins's and Franklin's data?
Guida verificata passo dopo passo1
Step 1: Understand Chargaff's rules, which state that in double-stranded DNA, the amount of adenine (A) equals thymine (T), and the amount of guanine (G) equals cytosine (C). This is because A pairs with T, and G pairs with C in the DNA double helix.
Step 2: Analyze the given nucleotide percentages: A = 29%, T = 19%, G = 21%, and C = 31%. Notice that the percentages of A and T are not equal (29% vs. 19%), nor are G and C equal (21% vs. 31%). This violates Chargaff's rules.
Step 3: Consider what Watson and Crick might conclude from this data. Since the base pairing rules require equal amounts of complementary bases, the unequal percentages would suggest that the DNA is not double-stranded or does not follow the base pairing model they proposed.
Step 4: Compare this conclusion to Wilkins's and Franklin's X-ray diffraction data, which provided evidence for a double helix structure with complementary base pairing. Their data implied equal base pairing, consistent with Chargaff's rules.
Step 5: Recognize the contradiction: if Chargaff's data showed unequal base pairs, it would conflict with the structural evidence from Wilkins and Franklin, challenging the double helix model and the concept of complementary base pairing.
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Chargaff's Rules
Chargaff's rules state that in DNA, the amount of adenine (A) equals thymine (T), and guanine (G) equals cytosine (C). This base pairing is fundamental to the double helix structure, ensuring complementary strands. Deviations from these ratios suggest an unusual or non-standard DNA structure.
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08:44
Genetics Basics
Watson and Crick's DNA Model
Watson and Crick proposed the double helix model where A pairs with T and G pairs with C, explaining Chargaff's equal base ratios. Their model relies on complementary base pairing to maintain consistent width and stability of the DNA molecule.
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09:32History and Experiments
X-ray Diffraction Data from Wilkins and Franklin
Wilkins and Franklin's X-ray diffraction images revealed the helical structure of DNA and consistent spacing between strands. Their data supported the double helix model and implied uniform base pairing, which would be contradicted by unequal base percentages as shown in the table.
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09:32History and Experiments
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