Physiology 3140A Study Guide - Quiz Guide: Small Interfering Rna, Microrna, Argonaute
22 May 2018
School
Department
Course
Professor
RNAi Module
RNA Interference
- Eukaryotic cells have endogenous mechanisms to repress mRNA translation called the RNAi
pathway
- Proteins in the RNAi pathway recognize and cleave long dsRNA into shorter pieces called short
interfering RNA (siRNA)
- Other proteins then use these siRNA to target mRNA sequences found in the cytoplasm for
degradation
- Used to take foreign double stranded RNA genomes from viruses that have infected our cells out
o Note: our genome also encodes for microRNA (which control what mRNA is being
translated)
- Can specifically target mRNA sequences for destruction by directly introducing siRNAs into
eukaryotes
- By inhibiting mRNA translation, function of a gene can be determined
o called knock down experiments
▪ where gene of interest is entirely removed from animal so that no mRNA can be
transcribed or translated
- VIDEO:
o Many animals use RNAi to control genes
o 2 important types of RNA : siRNA and microRNA
o eukaryotic cells have diff ways of controlling gene expression
o RNAi: using a group of molecules to direct gene silencing
o Inside nucleus,, most genes that encode proteins are transcribed by RNA poly 2
o The primary RNA transcript is processed by splicing and forms a mature mRNA
o The mRNA is exported into cytoplasm from nucleus
o Ribosomes then catalyze translation of mRNA to form polypeptide chains that fold into
proteins
▪ This is also were some small RNA molecules can have their silencing affects
o There are several types of regulatory small RNA (both about 21 nucleotides long)
▪ siRNA
• come from longer double stranded RNA that are either produced by cell
itself or are delivered into cell experimentally
• used to manipulate gene expression
▪ microRNA
• come from RNA transcribed in nucleus which then fold in a process
before being exported into cytoplasm as double stranded precursor
RNA
o the ds precursors of siRNA and microRNA bind to dicer (endonuclease protein that cuts
the RNA into short segments)
o the short ds RNA binds an argonaute protein
o one strand of the RNA is selected and remains bound to argonaute – called guide strand
o the combination of RNA and argonaute and other proteins is called the RNA induced
silencing complex (RISC)
o siRNA direct RISC to bind to specific RNAs
▪ the targeting is precise as its determined by base pairing bw siRNA and the
target mRNA
▪ siRNA have perfect complementarity to their target sites
▪ once bound, argonaute catalyzes cleavage of the mRNA which will then be
degraded
o microRNA also guide RISC to mRNA
▪ usually only a part of the microRNA (called the seed) pairs with the mRNA
find more resources at oneclass.com
find more resources at oneclass.com
