Question

1. For the lac operon, explain briefly what would happen and why regarding expression of the operon in each of the following scenarios. Be sure to include both positive and negative regulation in your explanation. a.) lactose is present, glucose is absent b.) lactose is absent, glucose is present c.) both lactose and glucose are present d.) lactose is present, glucose is absent, but there is a mutation to the sequence in the CAP site 2.) Consider the following RNA sequence, which represents the beginning of an open reading frame: 5’-AUGGGACUAGAUACC-3’. Examine each of the sequences below, describe the change to the sequence, and state whether it represents a silent, missense, nonsense, or frameshift mutation. If frameshift, be sure to include the consequences of the frameshift (nonsense or massive missense). Use the codon table in the textbook. a) 5’-AUGGGUCUAGAUACC-3’ b) 5’-AUGCGACUAGAUACC-3’ c) 5’-AUGGGACUAGUUACC-3’ d) 5’AUGGGACUAAGAUACC-3’ 3. Using a couple of sentences each, describe the function of each of the following in regulating eukaryotic gene expression: a) promoter b) enhancer c) histone acetyltransferase d) 5-methylcytosine

Answer 1

(1)

a.) lactose is present, glucose is absent: lac operon is turned on; positive regulation

b.) lactose is absent, glucose is present: Lactose is not the preferred carbohydrate source; lac operon is turned off. Negative regulation

c.) both lactose and glucose are present: If lactose and glucose are present, the cell will use all of the glucose; lac operon is turned off

d.) lactose is present, glucose is absent, but there is a mutation to the sequence in the CAP site: The binding of the CAP-cAMP complex to the promoter site is required for transcription of the lac operon. lac operon is turned off