miRNAs Flashcards
What are miRNAs?
- Tiny short RNAs (19-25 nucleotides).
- UNSTABLE!
- Found in all animals, plants and fungi. (5600 miRNAs In humans).
Where are miRNAs encoded?
miRNAs are encoded in the genome.
Some by stand alone genes (encode miRNAs)
Some within INTRON whose mRNA they will regulate.
Where are miRNAs expressed?
Expressed ONLY in certain cell types and ONLY certain times in the differentiation of a particular cell type.
What was the first miRNA discovered?
C. Elegans Lin 4
Who won Nobel prize for “discovery of RNA interference - gene silencing by double stranded RNA”?
Andrew Fire and Craig Melli In 2006
What are the functions of miRNA in the RNA silencing pathway?
- Silence genes from invading nucleus acids. Acts as a defense against invasive nuclei acids (eg: viruses, transposons, foreign genes).
- Also play a role in gene regulation - ESPECIALLY during DEVELOPMENT!
What processes does gene silencing target?
Stops translation RNA degradation Heterchromatin DNA degradation Stops transcription
What class do miRNAs belong to and what are they transcribed by?
miRNAs are class II and are transcribed by RNA Pol II
What is pri-miRNA processed by? And what is it processed into?
Drosha Protein converts pri-miRNA into pre-miRNA
Where does processing on pre-miRNA from miRNA gene take place?
Nucleus
What molecule exports pre-miRNA into the cytoplasm?
Exportin 5
What steps take place in the nucleus during miRNA processing?
miRNA gene - pri-miRNA - converted by Drosha to pre-miRNA and now will be exported from nucleus to cytoplasm by EXPORTIN 5
What happens when there is imperfect H-bonding between miRNA and Target?
Translation IS REPRESSED
What happens when there is PERFECT H-bonding of miRNA and Target?
mRNA is CLEAVED!
In cytoplasm, the pre-miRNA stem loop is cleaved by what?
A complex of dicer/R2D2
