Biology 9700 · AS & A Level · Structure of nucleic acids and replication of DNA

Structure of nucleic acids and replication of DNA — practice question

In 1953, James Watson and Francis Crick published information on the structure of DNA. They drew on experimental findings from other scientists to help determine the structure, then constructed a model of part of a DNA molecule using wire and metal pieces, with clamp stands supporting the model. This is shown in Fig. 2.1.
(a(i))[2]

Watson and Crick made use of findings from work done by Erwin Chargaff. He discovered that the proportions of the bases A, T, C and G differed between species, but within any one species: the proportion of A matched the proportion of T, and the proportion of G matched the proportion of C. Name the bases A, T, G and C.

(a(ii))[3]

Suggest and explain how Chargaff’s findings assisted Watson and Crick in working out the structure of DNA.

(b)[1]

Phoebus Levene separated the nucleotides of DNA and identified the carbohydrate part of each nucleotide. State the name of this carbohydrate component.

(c)[2]

Before the structure of DNA was discovered as the molecule of inheritance, scientists thought that proteins were the most likely molecules to carry information. Suggest how the structure of proteins made scientists think that these were the molecules that carried information.

Worked solution & mark scheme

This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: A=adenine, T=thymine, G=guanine, C=cytosine; every one correct for full marks.

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