Question

Gene expression includes transcription and translation to produce a protein product.  Below is a list of events that occur during eukaryotic gene expression.  Among the events listed, which event occurs first?  

Select one:

a. binding of the small ribosomal subunit to the mRNA

b. splicing out of the introns from mRNA

c. binding of release factor to the mRNA

d. binding of a charged tRNA to the first AUG codon

e. peptide bond formed to the initiator methionine

The map of the lac operon and repressor gene is presented

   here:

                                                I     POZYA

P is the promoter; O is the operator; Z encodes ß-galactosidase;

Y encodes lactose permease; A encodes a transacetylase.

The genotypes of merodiploids are shown below.  For each one, choose the correct phenotype from the table below.  (The same phenotype can be chosen for more than one genotype)

PHENOTYPE

                         ß-Galactosidase

            No lactose                                with lactose

A)                    -                                               +

B)                    -                                               -

C)                    +                                              +

D)                    +                                              -

I^--P⁺O^CZ^--/I⁺P⁺O⁺Z⁺

Select one:

a. A

b. B

c. C

d. D

The map of the lac operon and repressor gene is presented

   here:

                                                I     POZYA

P is the promoter; O is the operator; Z encodes ß-galactosidase;

Y encodes lactose permease; A encodes a transacetylase.

The genotypes of merodiploids are shown below.  For each one, choose the correct phenotype from the table below.  (The same phenotype can be chosen for more than one genotype)

PHENOTYPE

                         ß-Galactosidase

            No lactose                                with lactose

A)                    -                                               +

B)                    -                                               -

C)                    +                                              +

D)                    +                                              -

I^--P^--O^CZ^--/I⁺P^--O⁺Z⁺

Select one:

a. A

b. B

c. C

d. D

Answer 1

Ans-1- the very first event is transcription of mRNA. Second event is mRNA processing and the last event is translation. Option A, C, D, and E represents translation. Option B is mRNA processing. So option B is correct.

Ans-2- construct 1 has mutation in Z gene hence can't code for beta-galactosidase. In construct 2 every thing is normal and expression will only occur when lactose is present. So option A is correct.

Ans-3- since the promoter is mutated in both construct transcription can't occur. So option B is correct.