Question

RECALL What are the different terms used to describe the two strands of DNA involved in transcription?

Short answer

The template strand (antisense strand) and the coding strand (sense strand).

Step-by-step solution

- Identify the Process

Understand that transcription is the process of copying a segment of DNA into RNA.

- Naming the Strand that is Transcribed

The strand of DNA that is used as a template for RNA synthesis is called the 'template strand' or 'antisense strand.' It is complementary to the RNA strand that is produced.

- Naming the Non-Transcribed Strand

The strand of DNA that is not used for RNA synthesis is called the 'coding strand' or 'sense strand.' This strand has the same sequence as the RNA transcript (except that RNA contains uracil (U) instead of thymine (T)).

Key concepts

Template Strand

In the context of DNA transcription, the 'template strand' is the DNA strand that is read by RNA polymerase to create the RNA molecule. This strand is also known as the 'antisense strand.'
It serves as a template because its sequence is complementary to the RNA that is synthesized.
This means if the template strand has an adenine (A), the RNA synthesized will have a uracil (U), and if the template strand has a cytosine (C), the RNA will have a guanine (G).
This complementary nature is crucial because it ensures the RNA carries the correct genetic information.

Coding Strand

The 'coding strand' of DNA, also known as the 'sense strand,' is the strand that is not used during RNA synthesis. Despite its name, it does not code for RNA during transcription; instead, it has the same sequence as the RNA transcript that is produced, with the exception that thymine (T) is replaced by uracil (U) in RNA.
The coding strand is considered a 'reference' strand. It provides the same sequence as RNA, which can be crucial when comparing the RNA transcript to the original genetic code found in DNA.

• The coding strand's sequence is directly related to the sequence of amino acids in proteins because the mRNA is translated into proteins during a process called translation.
  This means that the coding strand essentially reflects the product of transcription.

RNA Synthesis

RNA synthesis, also known as transcription, is the process of creating an RNA copy from a DNA template. It occurs in three main stages: initiation, elongation, and termination.
During initiation, RNA polymerase binds to a starting point on the DNA, known as the promoter region. It then unwinds the DNA strands so that one strand can be used as a template.
In the elongation stage, RNA polymerase moves along the template strand, adding RNA nucleotides in the 5' to 3' direction, creating a growing RNA chain that is complementary to the DNA template.

• For example, if the DNA template strand reads ATCG, the growing RNA strand will read UAGC.

Finally, during termination, RNA polymerase reaches a sequence called the terminator, which signals the end of transcription. The RNA polymerase detaches from the DNA template, releasing the newly synthesized RNA. This new RNA strand can then undergo further processing before it is translated into a protein.