Gene expression can also be controlled after transcription. In eukaryotes and some prokaryotes, translation of the mRNA produced from target genes can be inhibited by RNA interference (RNAi). RNAi uses small, double-stranded RNA molecules to stop mRNA being translated.Small interfering RNA (siRNA)
1. An enzyme cuts double-stranded RNA into short pieces called siRNA.
2. One strand of the siRNA combines with an enzyme (part of a protein complex).
3. The siRNA strand guides the enzyme to an mRNA molecule with a complementary base sequence, where it binds by base pairing.
4. The enzyme cuts the mRNA into fragments, so it cannot be translated. The fragments are then broken down.Because siRNA is fully complementary to one mRNA, it silences one specific gene.MicroRNA (miRNA)
miRNA is made from the cell's own genes as a folded, hairpin-shaped RNA, which is processed into a short double-stranded miRNA. One strand joins a protein complex and binds to target mRNA. In mammals, miRNA is often not fully complementary to its target, so one miRNA can bind to several different mRNAs. Rather than cutting the mRNA, it usually blocks translation by stopping ribosomes moving along it. In plants, miRNA is usually fully complementary and the mRNA is cut, as with siRNA.
Cells use RNAi to regulate development and to defend against viruses. Scientists can make siRNA to switch off a chosen gene, which helps them find out what the gene does and could be used to treat diseases caused by an overactive gene.
1. An enzyme cuts double-stranded RNA into short pieces called siRNA.
2. One strand of the siRNA combines with an enzyme (part of a protein complex).
3. The siRNA strand guides the enzyme to an mRNA molecule with a complementary base sequence, where it binds by base pairing.
4. The enzyme cuts the mRNA into fragments, so it cannot be translated. The fragments are then broken down.Because siRNA is fully complementary to one mRNA, it silences one specific gene.MicroRNA (miRNA)
miRNA is made from the cell's own genes as a folded, hairpin-shaped RNA, which is processed into a short double-stranded miRNA. One strand joins a protein complex and binds to target mRNA. In mammals, miRNA is often not fully complementary to its target, so one miRNA can bind to several different mRNAs. Rather than cutting the mRNA, it usually blocks translation by stopping ribosomes moving along it. In plants, miRNA is usually fully complementary and the mRNA is cut, as with siRNA.
Cells use RNAi to regulate development and to defend against viruses. Scientists can make siRNA to switch off a chosen gene, which helps them find out what the gene does and could be used to treat diseases caused by an overactive gene.