Small interfering RNA

1. Small interfering RNA

2. Petunias Chalcone synthase White pigment Purple pigment

3. Producing a deep purple petunia Chalcone synthase White pigment Purple pigment More enzyme produced and more pigment formed Insert gene encoding chalcone synthase More mRNA synthesised

4. Producing a deep purple petunia Genetically engineered plant White plant Deep purple plant ? Instead of deep purple plants, many of the plants produced were white

5. Making double-stranded RNA mRNA is single stranded A U C A G U A C C C A G U A U C G RNA-dependent RNA polymerase Uses mRNA as a template to produce a complementary RNA strand U A G U C A U G G G U C A U A G C Two RNA strands held together by hydrogen bonds Double-stranded RNA (dsRNA)

6. What happens to double-stranded RNA? Double-stranded RNA is cut by Dicer enzyme • Small interfering RNA (siRNA) • Usually 21 base pairs long • Two base overhang at each end

7. Stopping protein synthesis We will start by simplifying the diagram of the siRNA molecule

8. Stopping protein synthesis We will start by simplifying the diagram of the siRNA molecule

9. Stopping protein synthesis siRNA forms a complex (RISC) with protein One of the siRNA strands is destroyed The siRNA–protein complex binds to mRNA

10. Stopping protein synthesis The mRNA is cut by the siRNA–protein complex The mRNA is then broken down. This prevents further protein synthesis

11. So why were white plants produced instead of deep purple plants? Genetically engineered plant White plant Deep purple plant ? Use the information about making double-stranded RNA and small interfering RNA to explain why.

12. The genetically engineered petunia plants had a higher concentration of mRNA This resulted in RNA-dependent RNA polymerase producing double-stranded RNA from this mRNA More siRNA molecules were formed that would bind to the mRNA coding for chalcone synthase Less chalcone synthase was produced so flowers were white, not deep purple