Q18.3-1CC. - Campbell Biology

Question

Compare miRNAs and siRNAs, including their functions.

Step-by-Step Solution

Answer

Both miRNAs and siRNAs are small RNAs but have minor differences in their structure. However, both are involved in gene regulation through RNA interference.

Step 1: MicroRNAs (miRNAs)

miRNAs are small RNAs that are approximately 22 nucleotides in length. They are single-stranded, and are produced from the action of cellular enzymes on long RNA molecules. These small RNAs bind with proteins to form a complex. 

The miRNAs base pairs with 7 to 8 nucleotides of the target mRNA. When the whole miRNA is entirely complementary to the target mRNA, the mRNA is degraded. However, if only a part of miRNA is complementary to the target mRNA, the translation process is blocked.

Step 2: Small interfering RNAs (siRNAs)

siRNAs are another class of small RNAs that is 21 to 23 nucleotides long. These are double stranded RNA molecules with a 3’ overhang. These are highly specific and bind to one target mRNA molecule. 

These molecules are involved in providing viral defense. siRNAs block the translation of mRNA molecules through RNA interference.

Step 3: Comparison of miRNA and siRNA

Both miRNAs and siRNAs are small RNA molecules. miRNAs are single-stranded, whereas siRNAs are double stranded. The difference in structure arises due to the difference in their precursor RNA molecule.

Both either degrade or block mRNA translation through RNA interference. miRNA acts as an endogenous regulator of gene expression, where siRNAs protect the cell from the virus and are involved in genome stability.

Thus, miRNA and siRNA are similar in nature and function. However, they have minor differences in their structure.