Difference Between CDS and cDNA

In molecular biology and genetics, understanding the structure and function of DNA and RNA sequences is essential for studying gene expression, protein synthesis, genetic engineering, and biotechnology applications. Two commonly used terms in gene analysis are CDS (Coding DNA Sequence) and cDNA (Complementary DNA).

Although both terms pertain to genes and their expression, they denote distinct concepts. CDS refers to the portion of a gene that encodes a protein, while cDNA is a DNA copy created from processed mRNA during reverse transcription. These concepts are critical for understanding gene structure, transcription, translation, recombinant DNA technology, and functional genomics.

1.0What Is CDS (Coding DNA Sequence)?

A CDS (Coding DNA Sequence) is the portion of a gene that is translated into a protein. It starts with a start codon (usually ATG) and ends with a stop codon (TAG, TAA, or TGA).

The CDS does not include:

• Promoters
• 5′ and 3′ untranslated regions (UTRs)
• Introns (in eukaryotic mRNA)

However, CDS includes only the base sequence that encodes amino acids.

Characteristics of CDS

• Found in both prokaryotic and eukaryotic genomes
• Represents the exact nucleotide sequence that determines protein structure
• Determined by exons in eukaryotes
• Length varies based on the protein encoded

Role of CDS

• Determines the amino acid sequence of proteins
• Used to predict protein function
• Essential for gene annotation and genetic engineering

Examples

2.0What is cDNA (Complementary DNA)?

cDNA (Complementary DNA) is synthesised from processed mRNA using the enzyme reverse transcriptase. It represents the coding region of an expressed gene, meaning it includes only sequences that were transcribed into mRNA and processed (spliced).

Unlike genomic DNA, cDNA does not contain introns or regulatory regions.

How cDNA Is Formed?

1. mRNA is extracted from expressing cells.
2. Reverse transcriptase synthesises a complementary DNA strand.
3. DNA polymerase forms the second strand, creating double-stranded cDNA.

Characteristics of cDNA

• Represents only expressed genes
• Contains only exons
• Used in cloning, expression vectors, PCR, and sequencing
• Varies based on tissue type and expression level

Role of cDNA

• Used for recombinant protein production
• Helps study gene expression patterns
• Important for constructing cDNA libraries

Examples

3.0Difference Between CDS and cDNA

4.0Similarities Between CDS and cDNA

• Both represent protein-coding information.
• Both exclude introns found in genomic DNA.
• Both are used in molecular cloning and protein analysis.
• Both allow prediction of amino acid sequences.
• Both help in studying gene function and expression.