Difference Between Template and Coding Strand

Main Difference – Template vs Coding Strand

Template and coding strand are the two terms that describe the two strands in the double-stranded DNA.  During transcription, one of the two strands in the double-stranded DNA serves as the template strand. The template strand runs in 3’ to 5’ direction. The other strand in double-stranded DNA, which runs from 5’ to 3’ direction is known as the coding strand. The template strand is responsible for the amino acid sequence in synthesizing the polypeptide chain. The main difference between template and coding strand is that template strand only serves as the template for transcription whereas coding strand contains the exact same sequence of nucleotides in the mRNA except thymine.

This article looks at,

1. What is Template Strand
     – Definition, Characteristics, Structure
2. What is Coding Strand
     – Definition, Characteristics, Structure
3. What is the difference between Template and Coding Strand

What is Template Strand

The template strand is the strand which serves as the template for the mRNA synthesis during transcription. Usually, RNA polymerase, which is the enzyme involved in the transcription of genes into mRNAs, adds nucleotides in the 5’ to 3’ direction to the growing strand of mRNA. Therefore, the template strand should be directed from 3’ to 5’ in order to add complementary nucleotides to the growing mRNA strand in the 5’ to 3’ direction. Hence, the DNA strand, which consists of 3’ to 5’ directionality in the double-stranded DNA, may serve as the template strand in transcription. That means, the template strand is the DNA strand in the double-stranded DNA which is responsible for the amino acid sequence of the synthesized polynucleotide chain. The other DNA strand in the double-stranded DNA is called non-template. The template strand is also called the antisense strand or the positive strand.

The template strand consists of a sequence of anti-codons which are the nucleotide triplets found in the tRNAs individually. The anti-codon is complementary to codons in the non-template or the coding strand. The synthesizing mRNA is temporally attached to the template strand by forming hydrogen bonds with the complementary nucleotides in the template strand. RNA polymerase adds uracil as the complementary nucleotide to the mRNA strand for adenine in the template strand instead of thymine. The template strand in the transcription is shown in figure 1.

Figure 1: Template Strand

What is Coding Strand

The DNA strand which serves as the non-template strand during transcription is referred to as the coding strand. Transcription is elongated in the 5’ to 3’ direction by adding complementary nucleotides to the mRNA strand. The coding strand also runs from 5’ to 3’ direction. Hence, coding strand is incapable of serving as the template during transcription. The coding strand contains codons, which are the nucleotide triplets which specify a unique amino acid in the polypeptide chain. These codons collectively make the genetic code, which is a universal feature in almost all the living forms on the earth. Coding strand during the transcription is shown in figure 2.

Figure 2: Coding Strand in the Transcription

The coding strand contains the same nucleotide sequence of the mRNA primary transcript. Therefore, bioinformatic tools like GLIMMER and GeneMark, which are involved in the finding of genes in a particular DNA sequence, depending on the coding sequence in order to predict genes in that particular DNA sequence. Since the coding strand contains similar sequences to the mRNA, the unique sequences in the mRNA-like start codon, stop codon and the open reading frame can be found in the coding sequence. These features, along with the sequences of the promoter, can be used by bioinformatics tools to predict genes by Ab initio method.

Difference Between Template and Coding Strand

Names

Template Strand: Template strand is also known as antisense strand, non-coding strand or negative strand.

Coding Strand: Coding strand is also known as either sense strand, non-template strand or positive strand.

Direction

Template Strand: Template strand is directed in the 5’ to 3’ direction.

Coding Strand: Coding strand is directed in the 3’ to 5’ direction.

Transcription

Template Strand: Template strand is transcribed into mRNA.

Coding Strand: Coding strand is not transcribed into mRNA.

Messenger RNA

Template Strand: Template strand contains the complementary nucleotide sequence as the mRNA.

Coding Strand: Coding strand contains the same nucleotide sequence to mRNA, except thymine.

Codon/Anticodon

Template Strand: Template strand contains anti-codons.

Coding Strand: Coding strand contains the codons.

Hydrogen Bonding

Template Strand: Hydrogen bonds are formed between the template strand and the synthesizing mRNA, temporary during transcription.

Coding Strand: No hydrogen bonds are formed between the coding strand and the synthesizing mRNA during transcription.

Transfer RNA

Template Strand: Template strand contains the same nucleotide sequence as the tRNA. 

Coding Strand: Coding strand contains the complementary nucleotide sequence as the tRNA.

Conclusion

The double-stranded DNA molecule is composed of two DNA strands, which are called template strand and coding strand. The template strand serves as the DNA template for transcription, which is the first step of gene expression. RNA polymerase adds complementary nucleotides to the nucleotides that are encoded in the template strand in order to form the primary RNA transcript. The addition of nucleotides occurs in the 5’ to 3’ direction. Hence, the directionality of the template strand should be 3’ to 5’. The non-template DNA strand, which runs in the 5’ to 3’ direction is referred to as the coding strand since it contains the same nucleotide sequence in the mRNA strand. Therefore, the main difference between template and coding strand is their ability to be transcribed by RNA polymerases.

Reference:
1. Alberts, Bruce. “From DNA to RNA.” Molecular Biology of the Cell. 4th edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 23 Mar. 2017.
2. “Sense (molecular biology).” Wikipedia. Wikimedia Foundation, 22 Mar. 2017. Web. 23 Mar. 2017.

Image Courtesy:
1. “0324 DNA Translation and Codons” By OpenStax –  (CC BY 4.0) via Commons Wikimedia
2. “Simple transcription elongation1” By Forluvoft – Own work (Public Domain) via Commons Wikimedia