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TLS Online TPP Program

#Question id: 3981

The diagram below represents a hypothetical operon in the bacterium E. coli.  The operon consists of two structural genes (A and B), which code for the enzymes A-ase and B-ase, respectively, and also includes P (promoter) and O (operator) regions as shown.

 When a certain compound (X) is added to the growth medium of E. coli, the separate enzymes A-ase and B-ase are both synthesized at a 50-fold higher rate than in the absence of X.  (X has a molecular weight of about 200.)  Which of the following statements is true of the operon decribed above?

#Unit 3. Fundamental Processes

  1. All four genes (A, B, O, and P) will be transcribed into an mRNA that will then be translated into four different proteins.

  2. The 3' end of the mRNA from the operon will correspond to the left end of the operon as drawn.

  3. The 5' end of the messenger from this operon will correspond to the right end of the operon as drawn.

  4. When RNA polymerase makes mRNA from this operon, it begins RNA synthesis just to the left of gene A.

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TLS Online TPP Program

#Question id: 33229

#Unit 1. Molecules and their Interaction Relevant to Biology

The effects of pH on enzymes depends on a combination of factors: 
(a) Most enzymes are active within only a narrow pH range, typically 5 to 9. 
(b) the ionization states of the amino acid residues involved in the catalytic activity of the enzyme
(c) the variation of protein structure (usually significant only at extremes of pH).
Which of the above is correct
TLS Online TPP Program

#Question id: 33230

#Unit 1. Molecules and their Interaction Relevant to Biology

The pH dependence of the rate of the reaction catalyzed by fumarase produces the following curve. Which amino acid/s likely to be present in the active site
TLS Online TPP Program

#Question id: 33231

#Unit 1. Molecules and their Interaction Relevant to Biology

Which character makes concerted acid–base catalysis a common enzymatic mechanism?
TLS Online TPP Program

#Question id: 33232

#Unit 1. Molecules and their Interaction Relevant to Biology

In RNase A 
TLS Online TPP Program

#Question id: 33233

#Unit 1. Molecules and their Interaction Relevant to Biology

The pH dependence of the rate of the RNase A reaction suggests the involvement of 
a. Two ionizable residues with pK values of 5.4 and 6.4
b. Single ionizable residue with pK values 7
c. Cytosine residue in active site
TLS Online TPP Program

#Question id: 33234

#Unit 1. Molecules and their Interaction Relevant to Biology

The form of catalysis is often also called nucleophilic catalysis