coding strand vs template

Daniel Parker

2 min read

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18-03-2025

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Understanding DNA replication requires grasping the difference between the coding strand and the template strand. These terms refer to the two strands of the DNA double helix during the process of creating a new DNA molecule. This article will clarify their roles and relationships.

What is the Coding Strand?

The coding strand, also known as the sense strand or non-template strand, is the DNA strand that has the same sequence as the mRNA molecule produced during transcription (except uracil (U) replaces thymine (T) in RNA). It doesn't directly participate in the process of DNA replication itself. Think of it as the "reference copy". Its sequence directly dictates the amino acid sequence of the resulting protein.

• It's not directly involved in replication: While it's crucial for protein synthesis, the coding strand doesn't act as a direct template during DNA replication.
• It's used as a reference: Its sequence is used to determine the sequence of the new DNA strand that's synthesized.
• It carries genetic information: The sequence of the coding strand holds the actual genetic code that determines traits.

What is the Template Strand?

The template strand, also called the antisense strand or non-coding strand, is the DNA strand that serves as the actual template for DNA replication and transcription. It's the strand that's read by DNA polymerase during replication and RNA polymerase during transcription.

• It's directly involved in replication: The template strand provides the pattern for building a new complementary DNA strand.
• It's read by polymerases: Both DNA and RNA polymerases use the template strand as a guide to create new strands.
• It's complementary to the coding strand: Its sequence is exactly complementary to the coding strand, following the base-pairing rules (A with T, and G with C).

The Replication Process: A Closer Look

During DNA replication, the DNA double helix unwinds, and each strand serves as a template for the synthesis of a new complementary strand. DNA polymerase reads the template strand and adds complementary nucleotides to build the new strand. This process results in two identical DNA double helices, each consisting of one original strand (the template) and one newly synthesized strand.

How the Strands Relate During Replication

Let's illustrate with an example:

Imagine a section of the coding strand: 5'-ATGCGT-3'

Its complementary template strand would be: 3'-TACGCA-5'

During replication:

1. The template strand (3'-TACGCA-5') is read by DNA polymerase.
2. DNA polymerase adds nucleotides to create a new strand that's complementary to the template: 5'-ATGCGT-3'.
3. The result is two identical double helices, each with one original (template) strand and one newly synthesized strand.

Transcription: The Role of the Template Strand

The template strand also plays a crucial role in transcription, the process of creating an RNA molecule from a DNA template. RNA polymerase uses the template strand as a guide to synthesize an mRNA molecule that's complementary to the template strand and therefore carries the same sequence as the coding strand (again, with uracil replacing thymine).

Key Differences Summarized

Conclusion

Understanding the distinction between the coding and template strands is essential for comprehending DNA replication and gene expression. While the coding strand carries the genetic code, it's the template strand that actively participates in these fundamental processes. Remember, both strands work together to ensure the accurate transmission of genetic information.