Difference Between Template and Coding Strand

The Difference between a template and a coding strand is primarily based on two characteristics: directional polarity and function. The two distinct strands of double-stranded DNA are the template strand and the coding strand, with the former functioning as a base to transcribe mRNA and the latter determining the correct base sequence of the mRNA.

Directional Polarity: The template strand moves from the 3’end to the 5’end, while the coding strand moves in the opposite direction, from the 5’end to the 3’end.

Base Sequence: The base sequence of the template strand is complementary to both the coding and mRNA strands. In contrast, the base sequence of the coding strand is identical to that of the new mRNA strand with the exception of the substitution of uracil for thymine.

The primary focus of this session will be on the main differences between the template and coding strand, as well as the comparison chart. In addition, you will learn the definitions and examples of each term.

Difference Between Template and Coding Strand

The template strand and coding strand are two complementary DNA strands that play distinct roles in molecular processes such as RNA synthesis and protein coding. Here are the key differences between the template strand and the coding strand:

1. Alternative Names: The template strand is also known as the antisense, minus, or non-coding strand, while the coding strand is referred to as the sense, plus, or non-template strand.
2. Function: The template strand acts as the template during RNA synthesis, serving as a guide for the production of RNA molecules. On the other hand, the coding strand determines the sequence of the RNA strand that is synthesized.
3. Directional Polarity: The template strand moves in a 3′-5′ direction, meaning that it is read by enzymes in the opposite direction. In contrast, the coding strand moves in a 5′-3′ direction, which corresponds to the direction in which enzymes synthesize new DNA or RNA strands.
4. Reading by RNA Polymerase: During transcription, RNA polymerase reads the template strand from the 3′ end to the 5′ end, using it as a template to synthesize an RNA molecule. The coding strand, however, is not directly read by RNA polymerase during this process.
5. Nucleotide Base Sequence: The base sequence of the template strand is complementary to both the coding strand and the resulting mRNA molecule. In contrast, the base sequence of the coding strand is identical to the newly formed mRNA, except that thymine (T) is replaced by uracil (U) in RNA.
6. Genetic Coding: The template strand contains sequences called “anticodons,” which are involved in complementary base pairing with codons in mRNA during translation. The coding strand, on the other hand, contains sequences called “codons” that correspond to specific amino acids during protein synthesis.
7. Formation of Hydrogen Bond: During transcription, a temporary hydrogen bond forms between the template strand and the newly synthesized mRNA. This bond helps stabilize the interaction between the template and the growing RNA molecule. In contrast, no such hydrogen bond forms with the coding strand during these processes.

Understanding the differences between the template strand and the coding strand is crucial for deciphering genetic information, studying gene expression, and unraveling the mechanisms of protein synthesis and RNA transcription.

Comparison Chart Between Template and Coding Strand

Property	Template Strand	Coding Strand
Alternative Names	Antisense, Minus or Non-coding Strand	Sense, Plus or Non-template Strand
Function	Acts as the template for RNA synthesis	Determines the sequences of the RNA strand
Directional Polarity	Moves in a 3’-5’ direction	Moves in a 5’-3’ direction
Reading by RNA Polymerase	RNA polymerase reads the template strand from 3’ to 5’ end	RNA polymerase does not read the coding strand
Nucleotide Base Sequence	Base sequence is complementary to both coding strand and mRNA	Base sequence is the same as the newly formed mRNA, but with uracil replacing thymine
Genetic Coding	Template strand has “Anticodons”	Coding strand has “Codons”
Formation of Hydrogen Bond	Hydrogen bond temporarily forms between template strand and newly synthesizing mRNA during transcription	No such bond forms

What is Template Strand?

• The template strand refers to one of the two DNA strands involved in the process of building mRNA through complementary base sequencing. It is also known as the “antisense strand” and runs in the 3′-5′ direction, opposite to the coding strand. The template strand contains nucleotide sequences that are complementary to the transcribed mRNA.
• During transcription, RNA polymerase recognizes the promoter genes or sequences on the template strand and uses it as a guide to produce an RNA transcript. This RNA transcript undergoes post-transcriptional modifications before it is converted into mature mRNA.
• The template strand also plays a crucial role in protein synthesis. It contains sequences called “anticodons,” which are triplet codes or nucleotide sequences complementary to the anticodon sequence of tRNA (transfer RNA). These anticodons facilitate the attachment of specific amino acids to tRNA molecules, forming a protein or peptide chain with the assistance of rRNA (ribosomal RNA).
• The RNA polymerase reads the template strand and synthesizes the RNA transcript by incorporating complementary nucleotides. The initiation of transcription and termination of translation processes are regulated by RNA polymerase.
• Overall, the template strand serves as a blueprint for mRNA synthesis and contains important information for protein production through its complementary base pairing with tRNA molecules. It plays a significant role in gene expression and protein synthesis in cells.

Example of Template Strand

Let’s consider an example of a template strand to understand its function in mRNA synthesis. Suppose we have a template strand with the gene sequence 5′-ATCGCGTA-3′. In this case, RNA polymerase (RNAP) will initially bind to the promoter region of the DNA sequence, initiating the process of transcription. The template strand will then be transcribed to form the primary mRNA transcript.

Since mRNA is formed with complementary base sequences to the template strand, the resulting mRNA sequence will be 3′-UAGCGCAU-5′. Each nucleotide in the mRNA sequence is complementary to the corresponding nucleotide in the template strand.

In this example, the template strand provides the necessary information for the synthesis of mRNA. The base pairing rules dictate that adenine (A) in the template strand corresponds to uracil (U) in the mRNA, thymine (T) corresponds to adenine (A), cytosine (C) corresponds to guanine (G), and guanine (G) corresponds to cytosine (C).

The resulting mRNA sequence, 3′-UAGCGCAU-5′, carries the genetic information transcribed from the template strand. This mRNA can then undergo further processing and modifications, such as the addition of a poly-A tail and removal of introns, to become a mature mRNA molecule ready for translation into a protein.

This example illustrates how the template strand serves as a template during transcription, guiding the synthesis of an mRNA molecule with complementary base sequences to ensure accurate transfer of genetic information.

What is Coding Strand?

• The coding strand, also known as the “sense strand,” is one of the two DNA strands that has a base sequence corresponding to the primary mRNA or the transcribed mRNA. The base sequence of the mRNA is similar to that of the coding strand, except that thymine (T) is replaced by uracil (U) in mRNA.
• The coding strand runs in the 5′-3′ direction, which is opposite to the template strand. While RNA polymerase (RNAP) utilizes the template strand to transcribe the mRNA, the coding strand acts as the complementary strand to the template strand. It carries triplet codons, which serve as the genetic code for specific amino acids during the process of protein synthesis through mRNA translation.
• Each codon on the coding strand codes for a specific amino acid. The sequence of codons along the coding strand determines the sequence of amino acids in the protein being synthesized. This process of translating the nucleotide sequence of mRNA into the corresponding amino acid sequence is essential for protein synthesis.
• The coding strand plays a vital role in the genetic code, providing the blueprint for the formation of mRNA, which carries the instructions for protein synthesis. It ensures that the mRNA molecule accurately reflects the genetic information stored in the DNA coding strand.
• In summary, the coding strand is the DNA strand that has a base sequence matching the primary mRNA or transcribed mRNA. It runs in the opposite direction to the template strand and contains codons that specify the amino acids necessary for protein synthesis.

Example of Coding Strand

Let’s consider an example of a coding strand based on the template strand sequence 5′-ATCGCGTA-3′. According to the Watson and Crick model, the coding strand will produce complementary base pairs relative to the template strand.

In this example, the sense strand’s base sequence will be 3′-TAGCGCAT-5′. Each nucleotide in the sense strand is complementary to the corresponding nucleotide in the template strand. Adenine (A) in the template strand pairs with thymine (T) in the sense strand, cytosine (C) pairs with guanine (G), and guanine (G) pairs with cytosine (C).

During transcription, RNA polymerase (RNAP) binds to the promoter region of the DNA sequence and initiates the process of transcription. The template strand is then transcribed to form the primary transcript, which has a base sequence of 3′-UAGCGCAU-5′.

In this example, the coding strand provides the complementary sequence to the template strand, which ultimately determines the sequence of the transcribed mRNA. The primary transcript, with the base sequence 3′-UAGCGCAU-5′, carries the genetic information transcribed from the template strand and is further processed to become a mature mRNA molecule.

This example illustrates how the coding strand pairs with the template strand to generate a complementary mRNA sequence during transcription. The coding strand plays a crucial role in protein synthesis by providing the necessary genetic code in the form of codons that determine the sequence of amino acids in the resulting protein.

Key Differences Between Template and Coding Strand

1. Alternative Names:
   • Template strand: Minus strand, antisense strand, non-coding strand.
   • Coding strand: Plus strand, sense strand, non-template strand.
2. Function:
   • Template strand: It serves as the base for RNA synthesis during transcription.
   • Coding strand: It determines the correct nucleotide base sequence of the RNA strand.
3. Directional Polarity:
   • Template strand: It runs in the 3′-5′ direction.
   • Coding strand: It runs in the opposite direction, 5′-3′.
4. Reading by RNA Polymerase:
   • Template strand: RNA polymerase reads the template strand from the 3′-5′ direction and synthesizes the RNA transcript by adding complementary nucleotides relative to the template.
   • Coding strand: RNA polymerase does not directly read the coding strand.
5. Nucleotide Base Sequence:
   • Template strand: Its base sequence (3′-5′) is complementary to the base sequence of both the coding strand and the resulting mRNA transcript (5′-3′).
   • Coding strand: Its base sequence is the same as the newly formed mRNA, except thymine (T) is replaced by uracil (U) in mRNA.
6. Genetic Coding:
   • Template strand: It contains tRNA anticodons, which carry triplet nucleotide sequences complementary to the anticodon sequence of tRNA.
   • Coding strand: It includes codons, which are triplet nucleotide sequences that code for specific amino acids to form a peptide chain.
7. Formation of Hydrogen Bond:
   • Template strand: During transcription, a temporary hydrogen bond forms between the template strand and the newly synthesized mRNA.
   • Coding strand: No such hydrogen bond forms between the coding strand and the mRNA.

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