Final - Lactose

Question 1

What does the Z gene on the Lac operon code for?

Select one:

a. Beta Galactosidase
b. Thiogalactoside Transacetylase
c. Lac Repressor
d. RNA Polymerase
e. Lactose Permease

Answer 1

a. Beta Galactosidase

Question 2

An assay of which of the following solutions will theoretically have the highest amount of b-galactosidase enzyme activity?

Select one:

a. Luria Broth, glucose and lactose, at 70 mins of incubation
b. Luria Broth, glucose and lactose, at 20 mins of incubation
c. Luria Broth & glucose, at 20mins of incubation
d. Luria Broth and lactose, at 70 mins of incubation
e. Luria Broth and lactose, at 20 mins of incubation

Answer 2

d. Luria Broth and lactose, at 70 mins of incubation

Question 3

Tamique tested E. Coli B-Galactosidase activity but the buffer solution she used for the B-Gal assay was 4 pH units higher than the optimal pH. What problem did Tamique observe?

Select one:

a. The pH of the solution was too basic for B-Galactosidase to bind to o-nitrophenol.
b. The pH of the solution was too basic for B-Galactosidase to bind to ONPG.
c. No problems were observed.
d. The pH of the solution was too acidic for transcription of the B-Galactosidase gene.
e. The pH of the solution was too basic to disrupt the cell membrane.

Answer 3

b. The pH of the solution was too basic for B-Galactosidase to bind to ONPG.

Question 4

In the absence of lactose, what gene(s) on the lac operon is/are transcribed?

Select one:

a. X and Y genes
b. I gene
c. I and Z genes
d. Z gene
e. X, Y and Z genes

Answer 4

I gene

Question 5

What is the normal function of the protein product encoded by the I gene?

a. Cleaves lactose into glucose and galactose
b. Imports of lactose into the cell
c. Binds to the operator of the lac operon
d. Binds to the promoter of the lac operon
e. Binds to RNA polymerase

Answer 5

binds to the operator of the lac operon

Question 6

John wants to measure the activity of B-galactosidase using the same protocol followed by LS3 students. He performs the experiment correctly but instead of ONPG he mistakenly adds galactose to the cells after the chloroform step. How will his spectrophotometry results compare to those obtained with ONPG?
Choose one answer.
a. The OD600 will be higher because ONPG stops cell growth.
b. The OD600 will be lower because the cells need glucose to survive.
c. The OD420 will be higher because galactose is a product of B-galactosidase activity.
d. The OD420 be the same because B-galactosidase is not produced in the presence of galactose.
e. The OD420 be lower because it measures the presence of products from the breakdown of ONPG.

Answer 6

OD420 be lower because it measure the presence of products from the breakdown of ONPG

Question 7

When lactose is present which of the following occur together:
Choose one answer.
a. repressor is activated; transcription occurs
b. repressor is inactivated; transcription occurs
c. repressor is activated transcription blocked
d. repressor is inactivated; transcription blocked
e. None of the above

Answer 7

b. repressor is inactivated; transcription occurs

Question 8

In the b-galactosidase assay lab, what was the purpose of using the chloroform? Choose one answer.

a. To allow cellular proteins to diffuse out of the cell.
b. To change the color of the sample to yellow.
c. To stop the b-galactosidase from reacting with ONPG.
d. To optimize the pH of the samples.
e. To provide nutrients for bacterial growth.

Answer 8

a. To allow cellular proteins to diffuse out of the cell.