Question

With regard to miRNAs and siRNAs, which of the following statements is (are) correct? a. miRNAs are transcribed from endogenous genes. b. miRNAs are usually a perfect match to an mRNA. c. siRNAs are transcribed from endogenous genes. d. siRNAs cause mRNA degradation. e. both a and d

Short answer

The correct statements regarding miRNAs and siRNAs are options a and d.

Step-by-step solution

Determine the nature and role of miRNAs

MicroRNAs (miRNAs) are small non-coding RNA molecules derived from transcripts that have a stem-loop structure. The primary function of a miRNA is to down-regulate gene expression. Therefore, option a is correct, miRNAs are indeed transcribed from endogenous genes. However, they are not usually a perfect match to an mRNA, contradicting statement b.

Determine the nature and role of siRNAs

Small interfering RNAs (siRNAs) are a class of double-stranded RNA molecules, coinciding with 20-25 base pairs, involved in the RNA interference (RNAi) pathway, where they interfere with the expression of specific genes. They are not necessarily transcribed from endogenous genes, contradicting statement c. They act by causing mRNA degradation, which means that statement d is correct.

Compare and provide the answer

By comparing all the statements in the light of our discussion, we conclude that both statements a and d are correct about miRNAs and siRNAs respectively.

Key concepts

Non-coding RNA molecules

Non-coding RNA molecules are a fascinating and essential component of cellular biology. Unlike mRNA, which carries the code for proteins, non-coding RNAs do not translate into proteins.
These molecules often have regulatory roles in the cell that contribute to gene expression dynamics.

There are different types of non-coding RNA molecules and two of the most significant ones related to gene regulation are microRNAs (miRNAs) and small interfering RNAs (siRNAs).

• miRNAs: Typically derived from endogenous genes, miRNAs are small in size. They play a crucial role in gene expression by binding to target mRNA molecules. This binding usually shows imperfect pairing, leading to the inhibition of protein translation.
• siRNAs: These are often double-stranded and involved in the RNA interference pathway. Unlike miRNAs, they are not always derived from endogenous genes. siRNAs show perfect or near-perfect pairing with their mRNA targets, leading to mRNA degradation.

This distinction is crucial, as it underlies their unique functions in gene regulation and the broader RNA interference mechanisms in cells.

Gene expression regulation

Gene expression regulation is a fundamental process that ensures cells have the right amount of proteins at the correct times.
By controlling when and how genes are turned on or off, cells can respond to internal needs and external signals efficiently.

Non-coding RNAs like miRNAs and siRNAs play a pivotal role in this regulation.

• miRNAs: These molecules regulate gene expression primarily at the post-transcriptional level. By binding to target mRNAs, they can prevent the translation of these mRNAs into proteins, effectively lowering the expression levels of particular genes.
• siRNAs: In contrast, siRNAs guide the RNA-induced silencing complex (RISC) to complementary mRNA targets, promoting their degradation. This results in the reduction of these mRNA levels within the cell, silencing the expression of the associated genes.

Through these processes, cells maintain homeostasis and adapt to varying conditions, highlighting the importance of miRNAs and siRNAs in gene expression regulation.

RNA interference (RNAi)

RNA interference (RNAi) is a natural cellular process used by organisms to regulate the activity of genes.
This fascinating mechanism is essential for modulating gene expression, defending against viral genomes, and maintaining genome stability.

One of the key players in RNAi are small, non-coding RNA molecules, specifically siRNAs.

• siRNAs Function: siRNAs originate from the cleavage of long double-stranded RNA molecules into smaller fragments. These fragments complex with proteins to form the RISC, which serves to target and degrade complementary mRNA sequences. By doing so, siRNAs effectively silence gene expression.
• miRNAs Involvement: While miRNAs are also part of the RNAi landscape, their role tends to focus more on translational repression rather than mRNA degradation. They are less involved in the RISC's RNA degradation pathway than siRNAs but are crucial for fine-tuning gene expression.

Through these roles, RNAi is not just a laboratory tool but a vital biological process, safeguarding cells from inappropriate gene expression and enabling precise regulation of cellular functions.