Question

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erwin chargaff (1905 - 2002), an austrian - american biochemist, investigated the ratio of nucleotide
bases found in the dna from a variety of organisms. from his research, as well as research by
rosalind franklin and maurice wilkins, watson and crick developed the complementary base - pair
rule during their race to discover the structure of dna. the complementary base - pair rule states that
adenine and thymine form pairs across two strands, and guanine and cytosine form pairs across two
strands.

1. fill in the complementary bases on the strand below according to the base - pair rule.

a t c c a g

1. the ladder model of dna is a simplified representation of the actual structure and shape of a

dna molecule. in reality, the strands of dna form a double helix. refer to the double helix
diagram in model 1 and describe its shape using a complete sentence.
18 dna structure and replication - s.docx
page 2

Explanation:

Step1: Recall base - pair rules

In DNA, adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G).

Step2: Fill in complementary bases

Given the sequence \(A\ T\ C\ C\ A\ G\), for each base:

• \(A\) pairs with \(T\)
• \(T\) pairs with \(A\)
• \(C\) pairs with \(G\)
• \(C\) pairs with \(G\)
• \(A\) pairs with \(T\)
• \(G\) pairs with \(C\)

Answer:

\(T\ A\ G\ G\ T\ C\)