How to determine which strand of DNA is transcribed into mRNA?

The template strand of DNA is read in the 3' to 5' direction. The newly synthesized RNA strand is formed in the 5' to 3' direction; it runs in the opposite direction of the template strand. Hence, if the newly synthesized strand is synthesize in the 5' to 3' direction, the template strand is read in the 3' to 5' direction.

And contra another of his claims, the coding strand is not the strand that gets transcribed into RNA, the template strand does. The DNA strand that is not transcribed is called the coding strand because, except for DNA having T and RNA having U, that DNA strand's sequence is the same as the primary RNA transcript's sequence, since they are both complementary to the template strand.


You don't have to take my word for it (even though unlike our person who doesn't know biology but claims to be a professor from Harvard, I actually do have a degree in biology), here's an undergrad cell biology text confirming what I said ...

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“(1) In contrast to DNA replication, where both DNA strands are copied, only one of the two DNA strands – the template strand – serves as a template for mRNA formation during transcription. The nontemplate DNA strand, although not directly involved in transcription, is by convention called the coding strand because it is similar in sequence to the single-stranded mRNA molecules that carry the coded message. … During DNA replication the base A pairs with T, whereas in transcription the base A pairs with U. Hence the sequence of the mRNA molecules is not exactly the same as the DNA coding strand, in the mRNA contains the base U anywhere the coding DNA strand has the base T.