Summary
About 22-nucleotide RNAs that fine-tune gene expression by blocking translation or promoting mRNA decay.
In depth
miRNAs are processed from hairpin precursors by Drosha and Dicer, and partially pair with 3' UTRs, repressing translation or destabilising mRNA. A single miRNA may regulate hundreds of genes.
They shape development, and abnormal levels appear in cancers.
Over 2000 human miRNAs are known, and each pairs with a seed region of about 6 to 8 nucleotides, so a single miRNA can have hundreds of targets, and each mRNA can be controlled by many miRNAs. The first, lin-4, was found in C. elegans by Ambros and Ruvkun in 1993, work recognised by the 2024 Nobel Prize in Physiology or Medicine.
miRNAs fine-tune development, immunity and metabolism. Some act as oncogenes (miR-21) and others as tumour suppressors (let-7). Circulating miRNAs in blood are studied as disease biomarkers.
Example: miR-122 is abundant in liver, and hepatitis C virus needs it to replicate, which was targeted by the drug miravirsen.
Frequently asked questions
What is microRNA?
About 22-nucleotide RNAs that fine-tune gene expression by blocking translation or promoting mRNA decay.
Which area of biology covers microRNA, and how advanced is it?
microRNA is one of the 52 topics in Molecular Biology. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include RNA Interference, Gene Expression, Long Non-Coding RNA.
Can you give an example of microRNA?
Lin-4 and let-7 control developmental timing in worms.
What should I learn before microRNA?
Work through the Beginner topics in Molecular Biology first, such as Central Dogma, DNA Replication, Base Pairing, then return to microRNA. Advanced topics assume the Intermediate vocabulary.
What topics are related to microRNA?
The closest topics to microRNA are RNA Interference, Gene Expression, Long Non-Coding RNA, Riboswitches. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand microRNA?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for microRNA. To practise the whole of Molecular Biology, use the Molecular Biology quiz.
How is microRNA different from RNA Interference?
microRNA: About 22-nucleotide RNAs that fine-tune gene expression by blocking translation or promoting mRNA decay. RNA Interference: Small interfering RNAs guide the RISC complex to degrade matching mRNA and silence genes. Read both side by side and note what each one explains.
How should I study microRNA step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with RNA Interference and explain the difference aloud. Finally, take the Molecular Biology quiz and come back to this page for any question you miss.