MicroRNAs

These flashcards cover key concepts related to microRNAs, their biogenesis, function, and role in gene regulation and disease.

What are microRNAs (miRNAs)?

Small, non-coding RNAs that regulate gene expression post-transcriptionally by suppressing target mRNAs.

Where do miRNAs usually bind their target mRNAs?

Most commonly the 3′ UTR.

Why are miRNAs important?

They are critical for normal development and many biological processes, and they are implicated in disease.

What is the first step in miRNA biogenesis?

miRNAs are transcribed by RNA polymerase II into primary miRNA (pri-miRNA).

What complex cleaves pri-miRNA into pre-miRNA?

The Drosha–DGCR8 complex.

How does pre-miRNA leave the nucleus?

Exportin-5 transports pre-miRNA through the nuclear pore complex (NPC) in a complex with Ran-GTP.

What does Dicer do to pre-miRNA in the cytoplasm?

Processes pre-miRNA into a mature miRNA duplex.

What happens to the passenger strand during RISC formation?

The passenger strand is degraded.

How does miRNA silence genes?

The miRNA–RISC complex binds complementary sequences in target mRNA, causing translational repression and/or mRNA degradation.

How do small GTPases act as molecular switches?

They cycle between inactive GDP-bound and active GTP-bound states.

What does Ran-GEF do?

Promotes GDP → GTP exchange, producing Ran-GTP in the nucleus.

What is the role of Ran-GAP?

Stimulates GTP hydrolysis to convert Ran-GTP to Ran-GDP in the cytosol.

What is the nuclear pore complex (NPC)?

A large protein complex that forms channels in the nuclear envelope and controls transport between nucleus and cytoplasm.

What is the purpose of post-transcriptional regulation by miRNAs?

To fine-tune protein output by reducing translation and/or destabilizing specific mRNAs.

What are miRNAs implicated in within the nervous system?

Regulating gene expression programs involved in neuronal development, synaptic function, and responses to stress/injury.

Give examples of CNS disorders linked to miRNA dysregulation.

Multiple CNS disorders; specific miRNAs (e.g., miR-20 family) have been studied as biomarkers and therapeutic targets.