Question

please answer all of them

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⁺Z⁺/I⁺P^--O⁺Z^--

Select one:

a. A

b. B

c. C

d. D

Two students begin a lab project with a 10 kb linear piece of DNA.  They digest it singly with EcoRI and Pst I, and then with the two enzymes together.  The results are listed below:

PstI      digestion yields two fragments, 7.5 and 3.5 kb.

EcoRI digestion yields two fragments, 8 and 2 kb

The Pst I, Eco RI double digestion yields three fragments 2, 4.5 and 3.5 kb.

Choose the best map of restriction sites for this piece of DNA

Select one:

a. A

b. B

c. C

d. D

e. E

The restriction enzyme BglII recognizes the 6 base sequence AGATCT, with the cleavage site between the A and the G, to give A GATCT.  The 4 base cutter Sau3A recognizes the sequence GATC and cuts before the first G.  This means

Select one:

a. there is a Sau3A site for every 2 BglII sites

b. every BglII site is also a Sau3A site

c. Sau3A fragments can never be cloned into BglII sites

d. Sau3A fragments will be bigger than BglII fragments on average

e. every Sau3A site is also a BglII site

Answer 1

1) Answer is Option A

The merodiploid can produce Lac I repressor. In the absence of lactose, the repressor will bind to the operator region and inhibits the synthesis of the beta-galactosidase enzyme. In the presence of lactose, the repressor is be removed from the operator site, which allows RNA polymerase to bind to the promoter region and to synthesize the beta-galactosidase enzyme.

2) The map will be - 2kb-4.5kb-3.5kb

Say the 2kb fragment generated by EcoRI digestion is present towards 5' end and the 8kb fragment is present towards 3' end. Say the 7.5kb fragment generated by PstI is present towards 5' end.

Now double digestion allows EcoRI to create a 2kb fragment and 8kb fragment. 8kb fragment is further cleaved by PstI to generate 4.5kb and 3.5kb fragments. So if 3.5kb fragment is present towards 3' end and 2kb fragment is present towards 5' end then the 4.5kb fragment must be within these two.

3) Answer is option b

Sau3A site is GATC, which is present within BglII site AGATCT. The bolded part is Sau3A cut site.