Question

1. Put the following steps of gene silencing by small interfering RNAs in the correct order:
   1. microRNA is folded and processed in the nucleus
   2. RISC binds to an mRNA molecule with bases complementary to the guide strand
   3. microRNA is transported into the cytoplasm
   4. microRNA is transcribed
   5. Argonaute protein selects one strand to act as the guide strand
   6. mRNA transcription is inhibited
   7. DICER cuts the microRNA into short segments (~21 nucleotides long)

Answer 1

• RNAi or RNA interference including Micro RNA or miRNA, 2) Small interfering RNA or siRNA.
• RNA interference has an ability of gene silencing, by inhibiting expression of genes.
• Micro RNA genes are transcribed by RNA polymerase II. Folding occurs nucleus, to produce about 70 nucleotide precursor RNA.
• siRNA originate from double stranded RNAs.
• The precursor is transported to the cytoplasm.
• They are produced by Dicer cleavage from longer strands.
• Dicer are helicase with RNAse motif.
• si RNA unwind into two single strands, one strand act as guide strand and other as passenger strand.
• The passenger strand binds with mRNA activating RNA-induced silencing complex (RISC) and is degraded. Only the guide strand binds to Argounate and activate it.
• Active catalytic component of RISC is Argonaute (AGO), which is an endonuclease, which can degrade m RNA.
• Ago protein null mutants lack gene silencing or viral protection properties.
• siRNAs act as defenders against foreign nucleic acids such as viruses, transposons, and transgenes, involving heterochromatin formation.

Answer: d-f-a-c-g-e-b