Question

RNAi may be directed by small interfering RNAs (siRNAs) or microRNAs (miRNAs); how are these similar, and how are they different?

Short answer

Short Answer: RNA interference (RNAi) is a gene-silencing mechanism involving small RNA molecules, including small interfering RNAs (siRNAs) and microRNAs (miRNAs). siRNAs and miRNAs are similar in size (21-23 nucleotides) and their involvement in forming the RNA-induced silencing complex (RISC). However, siRNAs arise from long double-stranded RNA precursors and exert a strong silencing effect by guiding RISC to complementary mRNA sequences. In contrast, miRNAs are derived from endogenous genes with hairpin-shaped precursors and typically bind to partially complementary sequences, exerting subtle and widespread regulatory roles in gene expression.

Step-by-step solution

Describe RNA interference (RNAi)

RNA interference (RNAi) is a process in cells where small RNA molecules (like siRNAs and miRNAs) regulate gene expression by targeting and degrading specific messenger RNA (mRNA) molecules or inhibiting their translation into proteins. This helps control the levels of proteins produced by genes within the cell.

Describe small interfering RNAs (siRNAs)

Small interfering RNAs (siRNAs) are small double-stranded RNA molecules typically generated from long double-stranded RNA precursors, which are processed into small 21-23 nucleotide long fragments. siRNAs function by incorporating one strand, known as the guide strand, into the RNA-induced silencing complex (RISC). The siRNA guide strand then directs the RISC to a complementary mRNA sequence, leading to the cleavage and degradation of the targeted mRNA, therefore silencing the expression of the corresponding gene.

Describe microRNAs (miRNAs)

MicroRNAs (miRNAs) are small single-stranded RNA molecules, approximately 21-23 nucleotides in length, derived from endogenous genes. miRNAs are produced from hairpin-shaped precursor molecules called pri-miRNAs and pre-miRNAs. The mature miRNA is incorporated into the RISC and can guide the RISC to partially complementary mRNA sequences. This process usually results in decreased translation or destabilization of mRNA, leading to gene silencing.

List similarities between siRNAs and miRNAs

1. Both siRNAs and miRNAs participate in RNA interference (RNAi) and function to silence the expression of specific genes. 2. Both types of RNA molecules are approximately 21-23 nucleotides in length. 3. Both siRNAs and miRNAs are involved in the formation of the RNA-induced silencing complex (RISC) to guide the targeting of specific mRNA molecules.

List differences between siRNAs and miRNAs

1. Origin: siRNAs are typically generated from long double-stranded RNA precursors, while miRNAs are derived from endogenous genes and have hairpin-shaped precursors in the form of pri-miRNAs and pre-miRNAs. 2. Target specificity: siRNAs guide the RISC to complementary mRNA sequences resulting in mRNA cleavage and degradation, while miRNAs typically bind to partially complementary sequences, leading to translational repression or mRNA destabilization. 3. Function: siRNAs typically have a stronger and more specific gene-silencing effect, while miRNAs often have more subtle and widespread regulatory roles in gene expression.