Q: Which enzyme is responsible for breaking down lactose into glucose and galactose in E. coli, and what is the chemical reaction it catalyzes?

β-galactosidase; $$\text{Lactose} + \text{H}_2\text{O} \rightarrow \text{Glucose} + \text{Galactose}$$

Question 1

Which enzyme is responsible for breaking down lactose into glucose and galactose in E. coli, and what is the chemical reaction it catalyzes?

Accepted Answer

β-galactosidase; $$	ext{Lactose} + 	ext{H}_2	ext{O} ightarrow 	ext{Glucose} + 	ext{Galactose}$$

Question 2

In the absence of lactose, what happens to the lac operon in E. coli?

Accepted Answer

The lac repressor binds to the operator, preventing transcription.

Question 3

Which of the following best describes the role of allolactose in the regulation of the lac operon?

Accepted Answer

Allolactose binds to the lac repressor, inactivating it and allowing transcription.

Question 4

What would be the effect on β-galactosidase production if a mutation occurred that prevented the lac repressor from binding to the operator?

Accepted Answer

β-galactosidase would be produced continuously, regardless of lactose presence.

Question 5

Which of the following conditions results in the highest level of lac operon transcription in E. coli?

Accepted Answer

Low glucose, high lactose

Question 6

How does the presence of glucose affect the transcription of the lac operon?

Accepted Answer

Glucose decreases cAMP levels, inactivating CAP and reducing transcription.

Question 7

Which of the following is NOT a specific component of the lac operon?

Accepted Answer

Gene for RNA polymerase

Question 8

What is the function of the CAP-cAMP complex in the regulation of the lac operon?

Accepted Answer

It increases the affinity of RNA polymerase for the promoter, enhancing transcription.

Question 9

Which of the following best describes the difference between structural and regulatory genes?

Accepted Answer

Structural genes encode enzymes and proteins with cellular functions, while regulatory genes encode proteins that control gene expression.

Question 10

Which of the following mutations would most likely decrease the ability of a cell to break down lactose?

Accepted Answer

Mutation in lacI so that repressor cannot bind inducer

Question 11

Which of the following statements about gene regulation in eukaryotes is TRUE?

Accepted Answer

Eukaryotic genes can be coordinately regulated even if they are scattered across different chromosomes.

Question 12

What is the effect of histone acetylation on chromatin structure and gene expression?

Accepted Answer

Histone acetylation loosens chromatin structure, enhancing transcription.

Question 13

Which of the following best describes epigenetics?

Accepted Answer

Epigenetics refers to heritable changes in gene expression that do not involve changes in DNA sequence.

Question 14

How can maternal diet during pregnancy affect the phenotype of offspring in mice, as shown in the Agouti gene example?

Accepted Answer

Maternal diet can alter DNA methylation patterns, affecting gene expression and phenotype.

Question 15

Which of the following mechanisms can regulate gene expression at the post-transcriptional level in eukaryotes?

Accepted Answer

Alternative RNA splicing

Question 16

What is the role of ubiquitin in protein regulation?

Accepted Answer

Ubiquitin tags proteins for degradation by the proteasome.

Question 17

If you examine the DNA isolated from a liver cell and a lens cell from the same person, how would the nucleotide sequence of the albumin enhancer in the liver cell compare with the sequence of the albumin enhancer in the lens cell?

Accepted Answer

The enhancer of the albumin in the liver cell has the same DNA sequence as the enhancer of the albumin in the lens cell.

Question 18

Which of the following best explains why different cell types in a multicellular organism can have different functions despite having identical DNA?

Accepted Answer

Different cell types express different sets of genes due to differential gene expression.

Question 19

Which of the following statements about the regulation of gene expression in bacteria is TRUE?

Accepted Answer

Bacteria can regulate gene expression at multiple levels, including transcription, translation, and post-translational modification.

Gene Regulation in Prokaryotes and Eukaryotes: The lac Operon and Epigenetic Control

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