Difference Between Sense and Antisense Strand

Main Difference – Sense vs Antisense Strand

Sense and antisense are the two terms that are used to describe the two strands in the double-stranded DNA, based on which strand serves as the template for the transcription. Sense strand contains the exact nucleotide sequence to the mRNA which encodes for a functional protein. Antisense strand serves as the template for the transcription, and contains complementary nucleotide sequence to the transcribed mRNA. Therefore, antisense strand is responsible for translating proteins. The main difference between sense and antisense strand is that sense strand is incapable of being transcribed into mRNA whereas antisense strand serves as the template for the transcription.

This article explores,

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

What is Sense Strand

The sense strand is considered as the coding strand of the double-strand DNA, which runs from 5’ direction to 3’ direction, based on the template strand which runs from 3’ to 5’ direction. It is considered in the positive sense. The sense strand contains the complementary nucleotide sequence to its antisense strand of double-stranded DNA. The mRNA contains the same nucleotide sequence as the sense strand, running from its 3’ to 5’ direction. Sense strand contains codons, which are the nucleotide triplets, specifying a unique amino acid in the polypeptide chain. Codons, which are used by genes to encode a functional protein are collectively called as the genetic code, which is considered as a universal feature of almost all the living forms. 

Figure 1: Sense and Antisense Strand

Just after following the transcription, resulting mRNA is called as the primary transcript. Primary transcript consists of the exact nucleotide sequence of the sense strand, except uracil, which is present instead of thymine. Additional editing can be undergone by the primary transcript before exposing to the post-transcriptional modifications. The removal of introns by splicing and the addition of 5’ cap and a 3’ poly-A tail are the post-transcriptional modifications, which involve in the production of a mature mRNA.

What is Antisense strand

The complementary strand to the sense strand in the DNA double-stranded is referred to as the antisense strand, which runs from 3’ direction to 5’ direction. The antisense strand is considered as in the negative sense. It serves as the template for the mRNA synthesis, transcription. Therefore, the antisense strand is responsible for the amino acid sequence of the translated polynucleotide. The antisense strand contains anti-codons, which are the nucleotide triplets found in tRNAs. The anti-codon is complementary to codon. During the transcription, RNA polymerase, which is the enzyme involving in the transcription add complementary nucleotides to the template strand. The synthesizing mRNA is temporarily attached to the template strand by the formation of hydrogen bonds with their complementary bases in the template strand. RNA polymerase adds uracil as the complementary base to adenine instead of thymine. 

The sense and antisense strands play a critical role in RNA interference inside the cell. RNA interference is a natural mechanism, which is used by cells in order to regulate the gene expression. During RNA interference, gene expression is knocked down by the production of an antisense DNA oligonucleotide strand, which can be complementarily base paired with the transcribed mRNA strand of a particular gene. The forming double-stranded RNA-DNA structure is cleaved off by Dicer protein complexes, clearing off the mRNA from the system. The mechanism in RNA interference is shown in figure 2.

Figure 2: RNA Interference Mechanism

Difference Between Sense and Antisense Strand

Direction

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

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

Transcription

Sense Strand: Sense strand is not transcribed into mRNA.

Antisense Strand: Antisense strand is transcribed into mRNA.

Messenger RNA

Sense Strand: Antisense strand contains the same nucleotide sequence as the mRNA, except thymine.

Antisense Strand: Antisense strand is the template strand for the RNA synthesis. Therefore, it contains the complementary nucleotide sequence to mRNA.

Codon/Anticodon

Sense Strand: Sense strand contains codons.

Antisense Strand: Antisense strand contains anti-codons.

Hydrogen Bonding

Sense Strand: No hydrogen bonds are formed between the sense strand and synthesizing mRNA.

Antisense Strand: Nucleotides in the antisense strand is temporarily hydrogen bonded with the complementary nucleotides in the synthesizing mRNA.

Transfer RNA

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

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

Conclusion

The two DNA strands in the double-stranded DNA are referred to as sense and the antisense strands. The naming of the two strands as sense and antisense is relative to the perspective to the template strand. Antisense strand, which runs from 3’ to 5’ direction serves as the template during transcription. The complementary nucleotides to the antisense strand are added to the mRNA strand by RNA polymerase enzyme. Sense strand runs from 5’ to 3’ direction, containing the same base pair sequence to the transcribing mRNA. Hence, sense strand is called as the coding strand. The antisense strand is called as the non-coding strand. It contains anti-codons, same as the tRNA. The main difference between sense and antisense strand is in their serving as the template for the transcription.

Reference:
1.Griffiths, Anthony JF. “Making Functional Transcripts.” Modern Genetic Analysis. U.S. National Library of Medicine, 01 Jan. 1999. Web. 23 Mar. 2017.

Image Courtesy:
1. “DNA transcription” By Dovelike – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Antisense DNA oligonucleotide” By Robinson R – RNAi Therapeutics: How Likely, How Soon? Robinson R PLoS Biology Vol. 2, No. 1, e28 doi:10.1371/journal.pbio.0020028 (CC BY 2.5) via Commons Wikimedia