6.8.1 Control Mechanisms: Lactose Metabolism in E. coli

Question 1

note

Answer 1

• Both prokaryotic and eukaryotic cells have mechanisms to regulate DNA and RNA. The process prevents cells from expending energy on unnecessary metabolic processes.
  • One such mechanism is found in E. coli, a species of bacteria that inhabits our digestive tract. The bacteria employ a regulatory process to control the synthesis of three enzymes responsible for lactose metabolism.
  • The lac operon is a regulatory unit on E. coli DNA that serves to control the synthesis of three enzymes responsible for metabolizing lactose. The three enzymes are B-galactosidase, permease, and transacetylase.
• The lac operon is a regulatory unit on the DNA strand that enables the bacteria to control the synthesis of enzymes involved in lactose metabolism.
• In the absence of lactose, these enzymes are not produced. The enzymes, as proteins, are synthesized through the processes of transcription and translation and require an expenditure of cellular energy. By regulating enzyme synthesis, cells conserve energy.

Question 2

In the presence of lactose, E. coli synthesizes three enzymes for digestion:

Answer 2

1. B-galactosidase breaks down lactose.
2. Permease is a membrane protein that transports lactose into the cell.
3. It is still unclear what role transacetylase plays in lactose digestion.

Question 3

True or false?
E. coli bacteria are a common contaminant in food and drinking water and are considered a threat to human health if present in the body.

Answer 3

• false

Question 4

True or false?

Gene regulation occurs at the level of the RNA.

Answer 4

• false

Question 5

Compared with eukaryotes, why are prokaryotes the more ideal subjects for studying gene regulation?

Answer 5

• Prokaryotes have a less complex cell structure than eukaryotes

Question 6

In a laboratory experiment, you culture E. coli cells. After switching their carbon source from glucose to lactose you find that the cells begin to produce

Answer 6

• lactose-digesting enzymes.

Question 7

What is the role of transacetylase in the metabolism of lactose by E. coli ?

Answer 7

• Its function is not clearly understood.

Question 8

______________ regulates mRNA transcription of enzymes responsible for digesting lactose in E. coli.

Answer 8

• The lac operon

Question 9

What is the role of beta-galactosidase in lactose metabolism?

Answer 9

• It breaks down lactose

Question 10

Which of the following enzymes does E. coli produce in the presence of lactose?

Answer 10

• beta-galactosidase
• permease
• trans-acetlyase
• All of these enzymes are made by E. coli in the presence of lactose.

Question 11

If several enzymes are necessary for a metabolic activity such as lactose metabolism,

Answer 11

• it is most efficient to produce the enzymes only when they are needed