Question

solving the structure of dna

1. complete the table to describe each scientists contribution to solving the structure of dna.

scientist contribution
erwin chargaff
rosalind franklin
james watson and francis crick

1. complete the table by estimating the percentages of each based on chargaffs rules.

dna sample percent of adenine percent of thymine percent of guanine percent of cytosine
1 31.5
2 30 20
3 17
the double - helix model
for questions 8 - 13, on the lines provided, label the parts of the dna molecule that correspond to the numbers in the diagram.

Explanation:

Question 6:

Step1: Erwin Chargaff

Chargaff analyzed the base composition of DNA from various organisms and found that 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).

Step2: Rosalind Franklin

She used X - ray diffraction techniques on DNA samples. Her famous Photo 51 provided key visual evidence about the helical structure of DNA, including the distance between the bases and the overall dimensions of the molecule.

Step3: James Watson and Francis Crick

Using Chargaff's rules and Franklin's X - ray data, they built a physical model of the DNA double - helix, showing how the two strands are antiparallel and held together by base - pairing.

Question 7:

Step1: For DNA sample 1

According to Chargaff's rules (A=T and G = C), if A = 31.5%, then T = 31.5%. The sum of A + T=63%. So the sum of G + C = 100 - 63=37%. Since G = C, G = C=37/2 = 18.5%

Step2: For DNA sample 2

If T = 30% and G = 20%, then A = 30% (because A=T) and C = 20% (because G = C)

Step3: For DNA sample 3

If C = 17%, then G = 17% (G = C). The sum of G + C = 34%. So the sum of A + T=100 - 34 = 66%. Since A=T, A = T=66/2=33%

Answer:

Question 6:

Scientist	Contribution
Rosalind Franklin	Took X - ray diffraction images of DNA that provided crucial structural information
James Watson and Francis Crick	Proposed the double - helix model of DNA structure

Question 7:

DNA sample	Percent of adenine	Percent of thymine	Percent of guanine	Percent of cytosine
2	30	30	20	20
3	33	33	17	17