Question:
Which of the following library you would prefer to screen to isolate a sequence that encodes a specific protein?
Which of the following library you would prefer to screen to isolate a sequence that encodes a specific protein?
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cDNA = "complementary DNA" synthesized from spliced mRNA. Because it is free of introns, cDNA is the only choice for expressing eukaryotic genes in prokaryotic host systems.
Updated On: Aug 7, 2026
- gDNA library
- cDNA library
- peptide library
- RNASeq library
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
Gene libraries are collections of cloned DNA fragments representing the genetic material of an organism.
The two primary types are genomic DNA (gDNA) libraries and complementary DNA (cDNA) libraries, each serving different experimental purposes.
Step 2: Detailed Explanation:
Let us compare gDNA and cDNA libraries for cloning protein-coding sequences:
gDNA Library (A): This library is prepared by digesting the entire genomic DNA of an organism.
In eukaryotes, genomic DNA contains both protein-coding regions (exons) and non-coding regions (introns).
If we clone a eukaryotic gene from a gDNA library into a bacterial expression system (like E. coli), the bacteria cannot process the introns because they lack the splicing machinery.
This results in a non-functional protein product.
cDNA Library (B): This library is prepared by isolating mature mRNA from cells and reverse-transcribing it into double-stranded DNA using reverse transcriptase.
Since mature mRNA has already undergone splicing to remove all introns, a cDNA clone contains a continuous, unbroken open reading frame (exons only) that encodes the exact sequence of the target protein.
This makes it highly suitable for expression in host cells to yield functional recombinant proteins.
Therefore, a cDNA library is preferred to isolate protein-coding sequences.
Step 3: Final Answer:
A cDNA library is preferred for isolating a sequence that encodes a specific protein, which corresponds to option (B).
Gene libraries are collections of cloned DNA fragments representing the genetic material of an organism.
The two primary types are genomic DNA (gDNA) libraries and complementary DNA (cDNA) libraries, each serving different experimental purposes.
Step 2: Detailed Explanation:
Let us compare gDNA and cDNA libraries for cloning protein-coding sequences:
gDNA Library (A): This library is prepared by digesting the entire genomic DNA of an organism.
In eukaryotes, genomic DNA contains both protein-coding regions (exons) and non-coding regions (introns).
If we clone a eukaryotic gene from a gDNA library into a bacterial expression system (like E. coli), the bacteria cannot process the introns because they lack the splicing machinery.
This results in a non-functional protein product.
cDNA Library (B): This library is prepared by isolating mature mRNA from cells and reverse-transcribing it into double-stranded DNA using reverse transcriptase.
Since mature mRNA has already undergone splicing to remove all introns, a cDNA clone contains a continuous, unbroken open reading frame (exons only) that encodes the exact sequence of the target protein.
This makes it highly suitable for expression in host cells to yield functional recombinant proteins.
Therefore, a cDNA library is preferred to isolate protein-coding sequences.
Step 3: Final Answer:
A cDNA library is preferred for isolating a sequence that encodes a specific protein, which corresponds to option (B).
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