The owners of a local bakery ask for your help in improving a special yeast strain they use to make bread. They would like you t
o help them design experiments using RNA interference to turn off genes, to allow them to test their hypothesis that certain genes are important for the good flavors found in their bread. Of the components in the following list, which is the most important to check for in this yeast strain if you would like this project to succeed? a. the presence of foreign double-stranded RNA
b. the presence of genes in the genome that code for RISC proteins
c. the presence of miRNA genes in the genome
d. the presence of single-stranded siRNAs within the cell
b. the presence of genes in the genome that code for RISC proteins
Explanation:
The RNA interference (RNAi) mechanism is a naturally occurring pathway by which eukaryotic cells can silence specific genes both at the transcriptional (eg., by triggering DNA methylation on specific <em>loci</em>) and posttranscriptional (e.g., by triggering mRNA degradation) levels. This mechanism (RNAi) is widely used in molecular biology laboratories in order to silence genes and thus understand their functions. During the RNAi pathway, double-stranded RNAs (dsRNAs) are cleaved into small double-stranded RNA (dsRNA) molecules known as small interfering RNAs (siRNAs) or microRNAs (miRNAs) by an enzyme referred to as "Dicer". Subsequently, these small non-coding RNAs bind to an enzymatic complex known as RNA-induced silencing complex (RISC) that contains a ribonuclease enzyme, i.e., an enzyme that degrades RNA. Finally, the small non-coding RNA (either siRNAs or miRNAs) that are complementary to the RNA target directs the RISC complex to bind and cleave specific mRNAs, thereby silencing gene expression (in this case, by the inhibition of protein translation).
Solution Cut open an onion. Use forceps to peel a thin layer of epidermis from the inside. Lay the layer of epidermis on a microscope slide. Add a drop of iodine solution to the layer. Carefully place a coverslip over the layer. Observe it under a microscope to see onion cells.
