What are Template Strand and Coding Strand?
The strand of DNA from which mRNA is formed after transcription is known as the template strand or the antisense strand. The template strand is usually directed 3’ to 5’ in direction. The coding strand or the sense strand corresponds to the same sequence as that of the mRNA strand.
The coding strand is not used as a template and it is reported to have 3 letter codons that code for amino acids. The amino acid sequence is then assembled to form protein. Keeping the similarities aside, the coding strand and the newly synthesized mRNA has a single difference i.e, thymine is present in the coding strand and uracil takes its place in the mRNA strand.
What is Meant by Antisense Strand?
The non-coding DNA strand of a particular gene is known as the antisense strand. The anti-sense strand serves as the template for transcription, which is a process of synthesis of mRNA that occurs in the nucleus of the cell. The mRNA formed then moves from the nucleus to the cytosol where the protein synthesis machinery comes into play and produces protein from the mRNA. This process is called translation. The anti-sense strand is meant by the strand that is complementary to the synthesizing mRNA and sense strand. It is also reported to contain anticodons. The DNA strand that is not used as a template in the transcription process is known as the sense strand.
Difference Between Template Strand and Coding Strand
Template strands and coding strands are discrete strands of the structure of DNA that differ by a few characteristics mentioned below.
Coding and Non-Coding Strand
The strand of DNA whose base sequence is similar to its primary transcript is known as the coding strand or the informational strand. This strand is reported to contain codons.
The non-coding strand or the transcribed strand, on the other hand, contains anticodons. RNA Polymerase II is reported to bind to the non-coding template strand, in the promoter site and reads the anti-codons.
After transcription of the sequence, a newly synthesized RNA transcript is produced with complementary bases. 99% of the DNA is made up of non-coding genes, hence, it was believed that the non-coding genes are junk. Recent studies by scientists proved that this non-coding portion of DNA contains regulatory elements that determine when a gene is turned on and when turned off.
Some regions of non-coding strand of DNA are reported to provide instructions for the synthesis of specialized RNA molecules such as transfer RNAs (tRNAs) and ribosomal RNAs (rRNAs), microRNAs (miRNAs), and long noncoding RNAs (lncRNAs), which has significant contribution in the regulation of gene activity.
Non Template Strand
The non-template strand is also known as the coding strand since its sequence is similar to the newly synthesized RNA molecule except for the inclusion of U in place of T. Recent research has shown an important role of the non-template strand specific-signal element of DNA in the terminal transcription bubble. It is believed to help in the process of transcription termination by RNA polymerase III.
Interesting Facts
Non-coding DNA strand is the antisense DNA of a gene that serves as the template for producing messenger RNA. It can make a copy of itself during mRNA synthesis. The coding strand is the DNA strand which cannot act as a template and its base sequence is similar to its primary RNA transcript.
Key Features of Template Strand and Coding Strand
The template strand contains the anti-codons while the coding strand contains the codons.
The polarity of the coding strand is in 3 the’ to 5’ direction, while the non-coding strand is directed in the 5’ to 3’ direction.
Coding DNA contains protein-coding genes and is composed of exons. Non-coding DNA does not code for proteins.
Non-coding DNA was considered junk but recent research has proved its importance in the proper functioning of cell and gene regulation.
FAQs on Template Strand and Coding Strand
1. What is the main difference between the template strand and the coding strand in a DNA molecule?
The primary difference lies in their roles during transcription. The template strand is the DNA strand that is actively read by the RNA polymerase enzyme to synthesize a complementary mRNA molecule. The coding strand is the other DNA strand, which is not used as a template but has a base sequence nearly identical to the resulting mRNA (with thymine 'T' instead of uracil 'U').
2. What is the specific function of the template strand during transcription?
The template strand, also known as the antisense strand, serves as the direct blueprint for creating messenger RNA (mRNA). RNA polymerase moves along the template strand in a 3' to 5' direction, reading its nucleotide sequence and synthesising a complementary RNA chain in the 5' to 3' direction. Its sequence is complementary to the final RNA transcript.
3. Why is one strand called the 'coding strand' if it is not used to make the RNA transcript?
This is a point of convention. The coding strand is called so because its DNA sequence corresponds directly to the codons found in the resulting mRNA transcript, just with thymine (T) in place of uracil (U). Geneticists often refer to the coding strand's sequence because it provides a quick, direct representation of the genetic code for a protein, making it easier to read and analyse gene sequences.
4. In which direction is the template strand oriented, and why is its polarity important?
The template strand is oriented and read in the 3' → 5' direction. This polarity is critical because the enzyme RNA polymerase can only synthesise new RNA by adding nucleotides to the 3' end of the growing chain. Therefore, to build the new mRNA strand in the required 5' → 3' direction, the enzyme must travel along the template strand in the opposite, 3' → 5', direction.
5. Can you provide a simple example of a template strand, coding strand, and the resulting mRNA?
Certainly. Consider a short segment of a gene:
- Coding Strand (5' → 3'): ATG GCC TTA
- Template Strand (3' → 5'): TAC CGG AAT
- Resulting mRNA (5' → 3'): AUG GCC UUA
Notice how the mRNA sequence matches the coding strand, with Uracil (U) replacing Thymine (T).
6. What would happen if the RNA polymerase enzyme used the coding strand as the template by mistake?
If the coding strand were used as the template, the resulting mRNA molecule would be complementary to it. This new mRNA would have a sequence completely different from the intended one. When translated, this incorrect sequence would either produce a non-functional protein or a completely different protein, potentially disrupting cellular function, as the codons for the amino acids would be entirely wrong.
7. Is the same strand of a chromosome always the template strand for every gene?
No, this is a common misconception. The designation of a strand as 'template' or 'coding' is gene-specific. For a given chromosome, some genes might use one of the DNA strands as the template, while other genes further along the same chromosome might use the opposite strand as their template. The choice depends on the location and orientation of the promoter region that initiates transcription for each specific gene.
