Question

The following segment of DNA is from a transcribed region of a chromosome. You know that RNA polymerase moves from left to right along this piece of DNA, that the promoter for this gene is to the left of the DNA shown, and that this entire region of DNA is made into RNA.

5′-GGCATGGCAATATTGTAGTA-3′

3′-CCGTACCGTTATAACATCAT-5′

Given this information, a student claims that the RNA produced from this DNA is:

3′-GGCATGGCAATATTGTAGTA-5′

Give two reasons why this answer is incorrect. (no more than two complete sentences)

Answer 1

5′-GGCATGGCAATATTGTAGTA-3′ ---Coding Strand

3′-CCGTACCGTTATAACATCAT-5′ ---Non-coding/template strand

1. RNA has Uracil in place of thymine. The strand the student claims to be transcribed has ‘T’ which must be replaced with ‘U’.

The correct strand will be 5′-GGCAUGGCAAUAUUGUAGUA-3′

2. Prime ends will be 5’ -> 3’. RNA polymerases synthesize RNA in 5’ to 3’ direction using non-coding strand as template. So the resulting RNA strand will be in 5’ to 3’ direction. A free 3’ end is needed for RNA polymerase to add bases.The bases will be as same as the coding strand (except U in place of T).