Question

Suppose that you are studying a positive inducible operon. TrcA is constitutively expressed and encodes an activator protein that can bind to fumarate, which acts as an inducer. The operon consists of three structural genes, TrcW, TrcX, TrcY that are transcribed upon activation of TrcA. Which of the following statements represents an observation you are likely to make in the course of your studies?

a. Expression of TrcA was turned off after addition of fumarate

b. None of the statements are likely to be observed in the study of this operon

c. Protein levels of TrcX were increased following addition of fumarate

d. Absence of fumarate resulted in activation of TrcA

e. Expression of TrcY, which processes fumarate into another form, resulted in enhanced expression of the operon

Polynucleotide phosphorylase was absolutely critical in helping scientists answer which research question?

a. Which part of a tRNA constitutes the anticodon sequence?

b. Which aminoacyl-tRNA synthetases coded for each amino acid?

c. Which amino acids are specified by codons consisting of one nucleotide?

d. Which proteins can bind to which DNA domains?Which aminoacyl-tRNA synthetases coded for each amino acid?

e. Which nucleotide sequences were critical for ribosome binding

Answer 1

Q1.

Answers is

c. Protein levels of TrcX were increased following addition of fumarate

Explanation:- TrcA encode the activator protein which binds to fumarate and activate expression of structural genes, TrcW, TrcX, TrcY. Therefore, upon addition of fumarate TrcX expression will be increases.

Following are the explanation why other options are wrong

a. Expression of TrcA was turned off after addition of fumarate

TrcA is the constitutively expressed therefore its expression is not depends on fumarate.

d. Absence of fumarate resulted in activation of TrcA

As it is positive inducible operon. Therefore absence of fumarate can't activate TrcA.

e. Expression of TrcY, which processes fumarate into another form, resulted in enhanced expression of the operon

If fumarate will converted to another form then it can't activate activator protein and therefore expression of operon will not enhanced.

Question 2.

Correct Answer is

c. Which amino acids are specified by codons consisting of one nucleotide?

Explanation: Polynucleotide phosphorylase has two key functions, first is degradation of RNA and second is polymerization by using substrate nucleoside diphosphates. In cell free system this enzyme will only shows polymerization activity. Therefore, If you provide substrate UDP (Uridine diphosphate) it will synthesize homopolymer poly(U). Therefore this homopolymer can be used to know which amino acid will code.