1. (1 points) A deletion mutation in the leader sequence of the trp operon removes the two tryptophan codons that are involved in attenuation. Predict the effect of this mutation on the expression of the trp structural genes in E. coli cells grown in media that lacks tryptophan. 2. (2 points) What protein family members are the main protein components of the RISC complex? How does the RISC complex target specific mRNAs for silencing? Degradation of homologous RNA in RNA interference is carried out by functional RNA-induced silencing complex (RISC). RISC contains Dicer, Argenaute proein, siRNA and other components The miRNA-RISC or siRNA-RISC complex binds to target, or complementary, mssengerRNA (mRNA) sequences, resulting in the enzymatic cleavage of the target mRNA. The cleaved mRNA is rendered nonfunctional and hence is “silenced.” 3. (3 points) In bacteria, the CRISPR/cas system targets specific DNA sequences found in phage (virus) genomes and degrades those sequences. How do cas enzymes recognize these DNA sequences? All biologists have to do is feed Cas9 the right sequence, called a guide RNA, and boom, you can cut and paste bits of DNA sequence into the genome wherever you want. Cas9 can recognize a sequence about 20 bases long, so it can be better tailored to a specific gene. All you have to do is design a target sequence 4. (3 points) Researchers have modified one particular cas enzyme, cas9, to target molecular functions other than endonuclease activity (degrading DNA) to particular loci in genomes. How is this accomplished?