Question

Compare miRNA to siRNA, highlighting similarities and differences in structure and processing events for mRNA degradation.

a) Both miRNA and siRNA have a similar structure, consisting of a double-stranded RNA molecule with a passenger and guide strand. They are processed in the cytoplasm by Dicer and incorporated into the RNA-induced silencing complex (RISC) for mRNA degradation.

b) miRNA and siRNA differ in their origin; miRNA is derived from endogenous non-coding transcripts, while siRNA is often exogenously introduced or originates from long double-stranded RNA. Both undergo Dicer processing and associate with RISC for mRNA degradation.

c) miRNA and siRNA have distinct structures; miRNA forms a hairpin loop structure, and siRNA is typically a perfectly complementary double-stranded RNA. Processing involves Dicer for both, leading to mRNA degradation through RISC.

d) miRNA and siRNA share a common processing pathway, involving Dicer and RISC, but differ in their target specificity; miRNA targets endogenous transcripts, while siRNA targets exogenous or viral RNA.

Answer 1

miRNA and siRNA are similar in structure and engage in RISC-mediated mRNA degradation, but differ in origin and complementarity to mRNA. miRNAs are endogenous with partial complementarity, regulating multiple mRNAs, while siRNAs are often exogenous with perfect complementarity, targeting foreign RNA.

Step-by-step explanation:

When comparing miRNA to siRNA, both share a similar structure as double-stranded RNA molecules, including a passenger strand and a guide strand. Once processed by the enzyme called Dicer, which reduces them into smaller fragments, they are incorporated into a complex known as the RNA-induced silencing complex (RISC) to facilitate mRNA degradation.

miRNAs are endogenously produced, often from non-coding regions of the genome and manifest as hairpin structures before their maturation. siRNAs, on the other hand, frequently originate from exogenous sources such as invaders like viruses, or from the cleavage of long double-stranded RNA indigenous to the cell. Both siRNAs and miRNAs, once processed by Dicer, can associate with RISC; however, siRNAs tend to have a perfect complementarity with their target mRNA resulting in cleavage and degradation, whereas miRNAs with incomplete complementarity can inhibit mRNA translation without necessarily causing RNA degradation.

It is important to note that miRNAs are involved in regulating endogenous gene expression and can target multiple mRNAs, which can be critical in processes such as development and disease, including cancer therapies. In contrast, siRNAs are generally involved in defending the cell against the introduction of foreign RNA, including viral genetic material.