Question

Hybridization of mRNA with DNA can reveal segments of DNA which are introns and exons; when the magnification is high enough to see the molecules, the introns appear as

• A. Single stranded loops in a double-stranded molecule.
• B. Separate fragments.
• C. Triple stranded nucleic acid molecule.
• D. Barr bodies.

Answer 1

The correct option is A Single stranded loops in a double-stranded molecule.

When a mixture of DNA and RNA is heated to denaturation temperatures to form single strands and then cooled, RNA can hybridize (form a double helix) with DNA that has a complementary nucleotide sequence. It is useful for determining relationships between DNAs and RNAs. Complementary DNA (cDNA) is double-stranded DNA synthesized from a messenger RNA (mRNA) template in a reaction catalysed by the enzyme reverse transcriptase. cDNA is often used to clone eukaryotic genes in prokaryotes. In RNA-DNA hybrid, single-stranded DNA loops are observed; these correspond to the introns in the gene. Since, these intron sequences in the viral genomic DNA are not present in mature exon mRNA, they loop out between the exon sequences that hybridize to their complementary sequences in the mRNA.