Question

analyzing data
chargaff’s rule
erwin chargaff was interested in the work of avery and did additional research on the structure of dna. one set of results from his experiments is shown in the data table. use the information to answer the questions.
percentages of bases in five organisms

source of dna	a	t	g	c
yeast	31.3	32.9	18.7	17.1
herring	27.8	27.5	22.2	22.6
human	30.9	29.4	19.9	19.8
e. coli	24.7	23.6	26.0	25.7

1. identify patterns what pattern do you identify in the data?

1. calculate if a species has 35 percent adenine in its dna, what is the percentage of the other three bases?

1. develop models all dna is composed of the four bases shown in the table. how is the pattern in the data useful for developing a model of dna?

Explanation:

1. For the pattern: The data shows that the percentage of adenine (A) is nearly equal to the percentage of thymine (T), and the percentage of guanine (G) is nearly equal to the percentage of cytosine (C) across all organisms.
2. For the calculation: Use Chargaff's Rule, where %A = %T, and %G = %C, with all bases summing to 100%.
3. For the model use: The consistent base pairing pattern (A-T, G-C) provides evidence that DNA has a complementary, double-stranded structure, where each base on one strand pairs with a specific base on the other strand.

Answer:

1. The percentage of adenine (A) is approximately equal to the percentage of thymine (T), and the percentage of guanine (G) is approximately equal to the percentage of cytosine (C) in each organism's DNA.
2. - Thymine (T): 35% (since %A = %T)

• Total of G + C: $100\% - (35\% + 35\%) = 30\%$
• Guanine (G): 15%
• Cytosine (C): 15%

1. The consistent base pairing pattern (A ≈ T, G ≈ C) supports the idea that DNA is a double-stranded molecule where adenine pairs only with thymine, and guanine pairs only with cytosine, which was critical for developing the double-helix model of DNA.