The genetic instructions for various cellular processes of living organisms are carried in the DNA molecule. DNA is the hereditary material, passing traits from parents to offspring. DNA has a double helix structure meaning, it consists of two long polynucleotide chains that are bound together by hydrogen bonds between A-T and G-C nucleotide base pairs. These chains are called DNA strands and the two strands are known as the coding strand and the template strand.
Both the coding and template strands are important components of the double-stranded DNA molecule, each with its own characteristics and roles in the transcription of mRNA. Both strands also play important roles in other cellular processes like replication and repair. However, the terms ‘coding strand’ and ‘template strand’ are specifically used for their roles in the transcription process.
During transcription, where RNA is made from DNA, one of these strands serves as the template. The RNA molecule produced is complementary to this template strand. The other strand, which is not directly used as a template during transcription, has the same sequence as the RNA molecule (except uracil replaces thymine). This strand is called the coding strand as its sequence corresponds directly to the mRNA sequence.
So, the coding strand and template strand are the two complementary strands forming the double helix structure of DNA, and they play crucial roles in processes like transcription and translation, which are essential for protein synthesis. Understanding the roles and characteristics of the coding and template strand is essential for understanding the processes of transcription and protein synthesis.
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Role of coding and template strand in Transcription
The coding and template strands work together to transcribe the genetic code into proteins. Both strands are vital in transcription, ensuring the transfer of genetic information from DNA to RNA.
The coding and template strands perform essential roles during the process of transcription. During transcription, mRNA is synthesized by the same process of complementary base pairing used in DNA replication, however, mRNA corresponds to only one strand of the DNA double helix unlike in DNA replication. This strand of DNA is called the template strand. The mRNA sequence is complementary to this template strand and identical to the other strand, known as the coding strand. RNA is synthesized by using the template strand of DNA as a guide for complementary base pairing.
The coding strand provides a reference for the formation of mRNA with a similar sequence, while the template strand guides the RNA polymerase to synthesize a complementary RNA strand. This way, both strands work together, ensuring the right information is transferred from DNA to RNA.
What is a Coding Strand?
The coding strand contains the same sequence as the mRNA, except for one difference: the replacement of thymine (T) in DNA with uracil (U) in mRNA.
The coding strand moves in the 5′ to 3′ direction, opposite to the template strand and it contains sequences that are complementary to the template strand. The coding strand contains codons which are groups of three nucleotides that code for specific amino acids during protein synthesis. Unlike the template strand, this strand doesn’t directly participate in the formation of mRNA during transcription. However, it is important because its sequence matches the mRNA’s sequence. While the template strand is being read and used as a template to create mRNA, the coding strand ensures that the resulting mRNA molecule is an exact copy of the coding strand.
What is a Template Strand?
The template strand of DNA plays a crucial role in the synthesis of mRNA through complementary base pairing.
It runs in the 3′ to 5′ direction, which is opposite to the direction of the coding strand and the mRNA. This strand does not participate in coding and is therefore referred to as the non-coding or anticoding strand. The template strand contains nucleotide sequences that are complementary to those found in both the transcribed mRNA and the coding strand so it is also known as the antisense strand. During transcription, RNA polymerase reads the template strand and directs the initiation of transcription. In contrast to the coding strand, the template strand guides the formation of mRNA through complementary base pairing, ensuring that the mRNA sequence is complementary to the coding strand.
Difference between Coding Strand and Template Strand
The major differences between the coding strand and template strand are summarized below:
| Coding Strand | Template Strand |
| The coding strand, also called the sense strand or the plus strand, is a crucial component of the DNA molecule. | The template strand, also referred to as the antisense strand or the minus strand, plays an important role in RNA synthesis. |
| Its main function is to determine the correct nucleotide sequence for mRNA during transcription. | It acts as the template for RNA synthesis, guiding the formation of mRNA. |
| The coding strand moves from 5′ to 3′ along the DNA molecule. | The template strand moves in the opposite direction, from 3′ to 5′. |
| RNA polymerase does not read the coding strand during transcription. | During transcription, RNA polymerase reads the template strand from 3′ to 5′. |
| The sequence of the coding strand is similar to the resulting mRNA, except for the substitution of uracil (U) for thymine (T). | The sequence of the template strand is complementary to both the coding strand and the mRNA. |
| The coding strand is referred to as the sense strand because it determines the protein-coding sequence. | The template strand is known as the antisense strand because it doesn’t directly code for proteins. |
References
- 28.4: Transcription of DNA – Chemistry LibreTexts
- Alberts, B., Johnson, A., Lewis, J., et al. (2002) Molecular Biology of the Cell. 4th Edition. Garland Science, New York. https://www.ncbi.nlm.nih.gov/books/NBK26821/
- Coding_strand (bionity.com)
- Difference between Coding Strand and Template Strand (byjus.com)
- Difference Between Template and Coding Strand (with Comparison Chart) – Biology Reader
- Griffiths A.J.F. et al. (2005) Introduction to Genetic Analysis (8th edition). W.H. Freeman and Company, New York, USA.
- Lewin B. (2000) Genes VII. Oxford University Press Inc., New York, USA.
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