Question

In order to express a recombinant protein that will be used for antibody production, you are given the choice to use either a genomic library or a cDNA library. Both are good libraries that have been screened to identify genes and proteins. You decide to use the cDNA library. This is because:

a. Introns have been removed from the mRNA and the exons spliced together to create an open reading frame in the transcript.

b. The cDNA contains the exons that encode the recombinant protein.

c. All of these

d. The cDNA library contains copies of mature processed and spliced mRNA

Answer 1

Complementary DNA or cDNA is produced by the reverse transcription of a fully processed and spliced mRNA using reverse transcriptase enzyme.

Since the mRNA is spliced, it means the introns have been removed and it contains only the exons that will code for the recombinant protein, therefore the cDNA library of such mRNA will be easier to use in comparison of the genomic DNA library that may contain the DNA sequence that will have both coding and non coding sequences. Genomic DNA consists of the entire genome and genomic library requires large artificial vectors for insertion of the large genomic DNA fragments. But cDNA only encodes the exons and is much smaller in size so can be inserted in the plasmid vectors.

Also in genomic DNA, all the genes are not expressed at the same time, some are expressed to form the proteins while some not. But cDNA contains only those genes that are expressed or are active in the cell.

cDNA libraries are used to express a protein found in eukaryotes in the prokaryotes as they cannot carry out splicing of the RNA molecule.

So from the given options, all the options are correct, hence correct option is c.