A genetics student was asked to draw the chemical structure of an adenine- and t

Question

A genetics student was asked to draw the chemical structure of an adenine- and thymine-containing dinucleotide derived from DNA. His answer is shown at left.

The student made more than six major errors. One of them is circled, numbered 1, and explained below the diagram.

Part A

Which of the following are other errors that the student made in the drawing?

Identify the six errors.

There are too few bonds between C-5 and C-6 of thymine. There are too many bonds between the N3 and C2 of thymine. The C-1? of the sugar is bonded to the wrong nitrogen in adenine. The phosphate is attached to the C-3? of the sugar rather than the C-2?. There is a hydroxyl group at C-2? on the top sugar (attached to adenine) instead of hydrogen. There is a methyl group missing from the C-5 position of thymine. In the adenine ring, a nitrogen is at position 8 rather than position 9. There is a hydrogen at C-2? on the bottom sugar (attached to thymine) instead of a hydroxyl group. There are too many bonds between the C-6 and N-1 of adenine.

Explanation / Answer

The six erors in the diagram are:

There are too few bonds between C-5 and C-6 of thymine

There are too many bonds between the N3 and C2 of thymine

The C-1? of the sugar is bonded to the wrong nitrogen in adenine

There is a hydroxyl group at C-2? on the top sugar (attached to adenine) instead of hydrogen

There is a methyl group missing from the C-5 position of thymine

In the adenine ring, a nitrogen is at position 8 rather than position 9

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