The eukaryotic gene Gen-100 contains four introns labeled A to D. Imagine that Gen-100 has been isolated and its DNA has been denatured and mixed with polyadenylated mRNA from the gene.

Illustrate the R-loop structure that would be seen with electron microscopy.

Verified step by step guidance

1. Identify the structure of the eukaryotic gene Gen-100, which includes exons and introns. Exons are the coding regions, while introns are non-coding regions that are spliced out during mRNA processing.
2. Understand that when the DNA of Gen-100 is denatured, the two strands separate, allowing the single-stranded mRNA to hybridize with its complementary DNA strand.
3. Recognize that the mRNA will only hybridize with the exonic regions of the DNA, as introns are removed during mRNA processing. This results in the formation of R-loops.
4. Visualize the R-loop structure: the mRNA-DNA hybrid forms a loop where the introns are located, as these regions do not have complementary mRNA to hybridize with.
5. Consider that under electron microscopy, the R-loop structure will appear as single-stranded DNA loops (representing introns) protruding from the double-stranded regions where mRNA is hybridized with the exonic DNA.

Key Concepts

R-loop Structure

An R-loop is a three-stranded nucleic acid structure formed when RNA hybridizes with a complementary DNA strand, displacing the non-template DNA strand. This occurs during transcription when mRNA is synthesized from a DNA template. The R-loop can be visualized using electron microscopy, revealing the regions where RNA is bound to DNA, which is crucial for understanding gene expression and splicing.

Introns and Exons

Introns are non-coding sequences within a gene that are transcribed into pre-mRNA but are removed during RNA splicing. Exons, on the other hand, are the coding sequences that remain in the mature mRNA and are translated into proteins. Understanding the roles of introns and exons is essential for interpreting the R-loop structure, as the presence of introns affects the hybridization pattern between mRNA and DNA.

Polyadenylated mRNA

Polyadenylated mRNA refers to messenger RNA that has a poly(A) tail added to its 3' end, which is crucial for mRNA stability, export from the nucleus, and translation efficiency. In the context of the R-loop, polyadenylated mRNA is used to hybridize with the denatured DNA, allowing for the visualization of the R-loop structure. This feature is important for understanding the functional aspects of gene expression.