Chapter 6/12

Question 1

Why do bacteria regulate gene expression?

Answer 1

To conserve energy and adapt to environmental changes.

Question 2

What is the structure of a bacterial genome?

Answer 2

Circular chromosome in the nucleoid + plasmids for special functions.

Question 3

Define an operon.

Answer 3

A cluster of genes under one promoter, transcribed together for coordinated function.

Question 4

What is the purpose of the lac operon?

Answer 4

To metabolize lactose when glucose is absent.

Question 5

How is the lac operon regulated when glucose is present?

Answer 5

CAP-cAMP is low → no activation → operon OFF.

Question 6

How is the lac operon regulated when glucose is absent and lactose is present?

Answer 6

Allolactose inactivates repressor; CAP-cAMP activates transcription → operon ON.

Question 7

What does CAP-cAMP do?

Answer 7

Activates transcription when glucose is low.

Question 8

Mutation: lacI⁻ (repressor gene deleted). Effect?
Operon ON always.

Answer 8

Operon ON always.

Question 9

Mutation: operator sequence altered. Effect?

Answer 9

Repressor cannot bind → operon ON always.

Question 10

Mutation: CAP protein defective. Effect?

Answer 10

No activation even if glucose is low.

Question 11

What is the purpose of the trp operon?

Answer 11

To synthesize tryptophan when levels are low.

Question 12

Q12: How does high tryptophan regulate the trp operon?

Answer 12

Repressor binds Trp → binds operator → transcription OFF; attenuation terminator loop forms.

Question 13

How does low tryptophan regulate the trp operon?

Answer 13

Repressor inactive → transcription ON; anti-terminator loop forms.

Question 14

What is attenuation?

Answer 14

Regulation via stem-loop structures in leader mRNA; controls transcription based on amino acid availability.

Question 15

Mutation: trpR⁻ (repressor gene deleted). Effect?
Operon ON always.

Answer 15

Operon ON always.

Question 16

Mutation: leader sequence altered. Effect?

Answer 16

Attenuation fails → operon ON even when Trp high.

Question 17

Name three ways bacteria acquire new DNA.

Answer 17

Conjugation (via pilus), transformation (uptake of naked DNA), transduction (phage-mediated).

Question 18

True or False: Bacteria reproduce sexually.

Answer 18

False.

Question 19

Which mutations act in cis vs trans?

Answer 19

Operator = cis; regulator protein = trans.

Question 20

In a trp operon null repressor mutant, how is transcription still repressed?

Answer 20

Attenuation mechanism.

Question 21

Where are bacterial chromosomes located?

Answer 21

In the nucleoid (not nucleus).

Question 22

What is maximal operon expression scenario in practice exam (donuts vs tears)?

Answer 22

When preferred energy source (donuts) is absent and alternative (tears) is present.

Question 23

Crybaby operon scenario: operator mutation vs regulator mutation?

Answer 23

Operator = cis; Crybaby regulator = trans.