8.2.9 RNA Interference

8.2.9 RNA Interference

How siRNA Works

1. Formation of siRNA:

• Double-stranded RNA (dsRNA) is cleaved into small interfering RNA (siRNA) by an enzyme called Dicer.

2. Binding to the RISC Complex:

• One strand of siRNA (the guide strand) binds to a protein complex called RISC (RNA-induced silencing complex).
• The complementary strand is discarded.

3. Targeting mRNA:

• The siRNA within the RISC complex binds to complementary sequences on mRNA molecules.
• This binding forms double-stranded mRNA, which is recognised as abnormal by the cell.

4. Degradation of mRNA:

• Enzymes within the RISC complex degrade the double-stranded mRNA.
• This prevents translation, effectively silencing the gene.

How miRNA Works

1. Formation of miRNA:

• MicroRNA (miRNA) is transcribed as a longer RNA molecule and then processed into shorter strands by enzymes like Dicer.

2. miRNA in RISC:

• miRNA binds to the RISC complex similarly to siRNA.
• However, miRNA is not fully complementary to its target mRNA, so it often inhibits translation rather than degrading the mRNA.

Key Differences Between siRNA and miRNA

Feature	siRNA	miRNA
Source	From double-stranded RNA	From single-stranded RNA
Complementarity	Fully complementary to mRNA	Partially complementary to mRNA
Mechanism	Degrades target mRNA	Inhibits translation

Applications of RNA Interference

1. Research:

• RNAi is used to study gene function by silencing specific genes in model organisms.

2. Therapeutics:

• RNAi is being developed to treat diseases like cancer and genetic disorders by silencing harmful genes.