The following DNA fragment was isolated from the beginning of a gene.

G G G A T G C G G A A A G T C C A A

C C C T A C G C C T T T C A G G T T

Determine which strand is transcribed, indicate the polarity of the two DNA strands, and then give the sequence of bases in the resulting mRNA and its polarity.

A strand that is transcribed is called a template strand, the other one is called a coding strand. The template strand is in 3'-5' direction, and the coding strand is in 5'-3' direction. mRNA is transcribed from 3'-5' template DNA strand, so it is in 5' to 3' direction. The first codon of mRNA is called start codon and usually it is AUG.

Knowing this, we can answer the questions:

The transcribed strand must contain three nucleotide sequence complementary to AUG codon. According to the base pairing rules, it must be TAC. The strand that contains TAC, and, thus, is transcribed is

C C C T A C G C C T T T C A G G T T.

This template strand is in 3'-5' direction and the other one is 5'-3'.

mRNA transcription begins from the DNA sequence complementary to AUG codon:

DNA sequence: 3' C C C T A C G C C T T T C A G G T T 5'

mRNA sequence: 5' A U G C G G A A A G U C C A A 3'

mRNA sequence is in 5'-3' direction.