Question

During transcription, the template strand is the one with the polarity:

• A. Always 3' to 5' as the template strand
• B. Always 5' to 3' as the template strand
• C. Any of the strands can become template strand.
• D. Alternatively both strand work as template strand.

Answer 1

Answer: (A)

Transcription occurs in only one direction. Thus the strand that has the polarity $3^{\prime }\to 5^{\prime }acts$ as the template strand. The other strand which has the polarity $5^{\prime }\to 3^{\prime }$ is referred to as the coding strand.
Transcription whether prokaryotic or eukaryotic has three main events.
$\cdot$ Initiation - Binding of RNA polymerase to double-stranded DNA; this step involves a transition to single strandedness in the region of binding; RNA polymerase binds at 5’ end on a sequence of DNA called the promoter. Initiation is the most important step in gene expression.
$\cdot$ Elongation - The covalent addition of nucleotides to the 3' end of the growing polynucleotide chain. This involves the development of a short stretch of DNA that is transiently single-stranded.
$\cdot$ Termination - The recognition of the transcription termination sequence and the release of RNA polymerase. The promoter and terminator flank the structural gene in a transcription unit.