Question

RNA interference (RNAi) is a natural process by which cells suppress the activity of specific genes by targeting and degrading mRNA. One way RNAi has been harnessed by agricultural scientists is to protect plants from pest attacks on the roots of corn plants.

Choose the answer below that correctly describes the steps in the RNAi process that eventually result in degradation of the target mRNA.

		1. The protein Dicer recognizes double-stranded RNA (dsRNA) 2. Dicer cuts up the dsRNA into small segments (still double-stranded). 3. RNA-Induced silencing complex (RISC) separates the two strands of the small segments. 4. RISC carries one strand of the small segment. 5. RISC uses that one strand to bind a complementary mRNA transcript. 6. Once the anti-sense strand is bound, RISC degrades the target mRNA.
		1. The protein Dicer recognizes double-stranded RNA (dsRNA). 2. Dicer cuts up the dsRNA into small segments (still double-stranded). 3. RNAi polymerase (RNAi poly) separates the two strands of the small segments. 4. RNAi poly carries one strand of the small segment. 5. RNAi poly uses that one strand to bind to a complementary mRNA transcript. 6. Once the anti-sense strand is bound, RNAi poly degrades the target mRNA.
		1. The protein Dicer recognizes double-stranded RNA (dsRNA). 2. Dicer cuts up the dsRNA into small segments 3. Dicer separates these small segments them into two single strands. 4. RNAi polymerase (RNAi poly) then picks up and carries one strand of the small segment. 5. RNAi poly uses that one strand to bind to a complementary mRNA transcript. 6. Once the anti-sense strand is bound, Dicer then recognizes this as double-stranded RNA, and subsequently cuts up the dsRNA, effectively degrading the target mRNA.
		1. The protein Dicer recognizes double-stranded RNA (dsRNA). 2. Dicer cuts up the dsRNA into small segments 3. Dicer separates these small segments them into two single strands. 4. RNA-Induced Silencing Complex (RISC) then picks up and carries one strand of the small segment. 5. RISC uses that one strand to bind to a complementary mRNA transcript. 6. Once the anti-sense strand is bound, Dicer then recognizes this as double-stranded RNA, and subsequently cuts up the dsRNA, effectively degrading the target mRNA.

Answer 1

1. The protein Dicer recognizes double-stranded RNA (dsRNA)

2. Dicer cuts up the dsRNA into small segments (still double-stranded).

3. RNA-Induced silencing complex (RISC) separates the two strands of the small segments.

4. RISC carries one strand of the small segment.

5. RISC uses that one strand to bind a complementary mRNA transcript.

6. Once the anti-sense strand is bound, RISC degrades the target mRNA.

RISC is a RNAi effector complex which consists of an Argonaute (Ago) protein. The Ago of the RISC cleaves and discards the sense strand of the siRNA duplex (incorporated into the RISC) leading to an active RISC. The antisense strand of the siRNA duplex guides the RISC to its homologous mRNA, resulting in the endo-nucleolytic cleavage of the target mRNA.