Question

1. Maximum gene expression for lac operon will occur by:

a. Glucose high, cAMP low, Lactose absent

b. Glucose low, cAMP high, lactose absent

c. Glucose low, cAMP high, lactose present

d. Glucose high, cAMP low, lactose present

2. RNA polymerases have which metal ion to aid in catalytic reactions?

a. Mg2+

b. Ca2+

c. Mn2+

d. Fe2+

Answer 1

1. Option C is the right answer.

This is because , Lac Operon functioning requires,cAMP and CAP. The cAMP attaches to CAP (catalytic activator protein) .

This complex binds to DNA regulatory sequences to bring transcription of mRNA and then translation to help in the lac operon expression. If glucose is present in the medium, cAMP is not formed, so CAP does not bind to DNA, resulting in no gene function.

If glucose is present, bacterium can use glucose for its energy. No need for lactase enzyme to be formed.Lactase(galactase) is formed only when glucose is not there and it uses lactose by digesting with galactase.

Low glucose levels and lactose present in the medium increases cAMP levels. CAP protein now binds to cAMP . The complex together binds to DNA .  The lac operon functions producing galactase for lactose digestion.

This way of controlling lac operon is called the +ve control.

2. Option 'a' is the right one.

RNA polymerases require metal ions for enzymatic activity. Mg and Zn are the cations act as co factors to RNA polymerases.