Suppose that a glutamine residue in the active site of an enzyme was mutated to alanine. as expected, the alanine mutant was inactive, suggesting that the glutamine residue was critical to the catalytic mechanism. which mutation is most likely to restore wild-type level of activity to the alanine mutant?

a to m

a to n

a to f

a to k

a to e

A to N

Explanation:

Glutamine is an amino acid with a polar, uncharged side chain. The mutation to alanine, an amino acid with a non-polar side chain, completely affects the enzymatic activity. This makes sense considering the difference in the nature of both amino acids.

To restore the wild-type level of activity the alanine would have to mutate to another polar uncharged amino acid. Among the given options, only Asparagine (N) has a similar chemistry to Glutamine.

protist eukaryotes that are not plants, animals, or fungi ("misfits")

step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.