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. Understand the concept of R-loops: R-loops are structures formed when a single-stranded RNA hybridizes with its complementary DNA strand, displacing the other DNA strand. This occurs during transcription when mRNA pairs with the template strand of the gene.
2. Identify the structure of the Gen-100 gene: The gene contains four introns (A, B, C, and D) and exons in between. Introns are non-coding regions that are spliced out of the mRNA, while exons are coding regions that remain in the mature mRNA.
3. Visualize the hybridization process: When the denatured DNA of Gen-100 is mixed with the polyadenylated mRNA, the mRNA will hybridize with the complementary DNA strand (the template strand). The exons in the mRNA will align with their corresponding regions in the DNA, while the introns will form loops because they are absent in the mRNA.
4. Illustrate the R-loop structure: The R-loop will consist of double-stranded regions where the mRNA is hybridized to the template DNA strand, and single-stranded loops corresponding to the introns (A, B, C, and D) that are not present in the mRNA. These loops will be visible under electron microscopy as protrusions.
5. Label the R-loop diagram: Clearly label the exons (aligned regions), the intron loops (A, B, C, and D), and the polyadenylated tail of the mRNA. This will help in understanding the relationship between the gene's DNA and its processed mRNA.

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. In the context of eukaryotic genes, R-loops can occur when mRNA binds to the DNA template, creating a loop that includes the coding sequence and excludes introns. This structure is significant for understanding gene expression and the processing of pre-mRNA.

Introns and Exons

Introns are non-coding sequences within a gene that are transcribed into pre-mRNA but are removed during RNA splicing, while exons are the coding sequences that remain in the mature mRNA. The presence of introns allows for alternative splicing, which can generate multiple protein variants from a single gene. Understanding the distinction between introns and exons is crucial for interpreting the R-loop structure in the context of gene expression.

Polyadenylated mRNA

Polyadenylated mRNA refers to messenger RNA that has a poly(A) tail added to its 3' end, which is important for mRNA stability, export from the nucleus, and translation efficiency. In the context of the question, the polyadenylated mRNA from the isolated gene Gen-100 would hybridize with the corresponding DNA, facilitating the formation of the R-loop structure. This characteristic is essential for understanding the interaction between mRNA and DNA during gene expression.