Lesson 8 Gene Regulation in Bacteria

Question 1

What is transcriptional regulation?

Answer 1

Gene regulation that occurs during transcription.

Question 2

What kind of gene regulation is most common in bacteria?

Answer 2

Transcriptional regulation

Question 3

What are the two types of regulatory proteins?

Answer 3

Repressors and activators

Question 4

Repressor protein

Answer 4

Regulatory protein that binds to the DNA to inhibit transcription

Question 5

Activator protein

Answer 5

Proteins that increase the rate of transcription

Question 6

Negative control

Answer 6

Transcriptional regulation by repressor proteins

Question 7

Positive control

Answer 7

Transcriptional regulation by activator proteins

Question 8

How does an effector molecule exert its effects?

Answer 8

It binds to a regulatory protein such as an activator or a repressor.

Question 9

Inducer

Answer 9

Small molecule that will cause transcription to increase

Question 10

Corepressor

Answer 10

Small molecule that binds to a repressor protein and causes protein to bind to the DNA

Question 11

Inhibitor

Answer 11

A molecule that binds to an activator protein and prevents it from binding to the DNA

Question 12

operon

Answer 12

Area in which two or more structural genes are under the transcriptional control of a single promoter

Question 13

Is it common for bacteria to have genes in operons?

Answer 13

yes

Question 14

What surrounds an operon?

Answer 14

A promoter to signal beginning of transcription and a terminator to signal the end of transcription.

Question 15

What regulates the promoter of an operon?

Answer 15

An operator site

Question 16

What does the lac operon do?

Answer 16

encodes proteins that are involved in lactose metabolism

Question 17

What is structure of lac operon?

Answer 17

It is made up of two units. The first is known as the lac Oberon and it contains a promoter and three structural genes, lacZ, lacY, lacA. Second unit, with its own promoter, is the lacI gene.

Question 18

What protein regulates the lac Oberon? H

ow?

Answer 18

Lac repressor protein. It binds to the operator site and prevents RNA polymerase from sliding past the operator site and transcribing the lacZ, Y and A genes.

Question 19

What dictates the ability of lac repressor to bind to operator site?

Answer 19

It depends on whether or not allolactose is bound to it. When allolactose binds to the repression, it causes a conformational change that prevents the lac repression from binding to the operator site. Under these conditions, RNA polymerase will transcribe the Oberon.

Question 20

What is induced?

Answer 20

Transcription is startedf

Question 21

What is repressed?

Answer 21

Repression is bound to the operator site, so there is no transcription.

Question 22

Experiment 14A: lacI gene

Hypothesis

Answer 22

If the lacI gene encodes a repressor protein, then the lacI gene itself does not have to be physically next to the lac Oberon to repress it; the protein can diffuse throughout the cell and bind to an operator site regardless of the physical location of the lacI gene.

Question 23

Experiment 14A: lacI gene

How were the data interpreted?

Answer 23

Yellow production in original mutant strain was same with or without lactose. This was expected because beta-galactosidase there was constitutive.
In merozygote, an absence of lactose repressed lac operons. With lactose, both operons (the one on chromosome and the one on the F’ factor) were induced, yielding a higher level of beta-galactosidase activity in the merozygote.

Question 24

Trans-effect

Answer 24

Form of genetic regulation that can occur even though two DNA segments are not physically adjacent.

Question 25

cis-effect or CIS-acting element

Answer 25

DNA segment that must be adjacent to the gene(s) it regulates

Question 26

Experiment 14A: lacI gene

What was difference between mutant and merozygote strains?

Answer 26

Mutant strain was lacI-, lacZ+, lacY+, lacA+

Merozygote was lacI+ and above

Question 27

Why does intracellular concentration of cAMP decrease when a bacterium is exposed to glucose?

Answer 27

The presence of glucose inhibits adenylate cyclase, which is necessary for cAMP synthesis. This decreases rate of transcription. This enables bacteria to use two sugars in a more efficient way. First, they will use glucose, then lactose.

Question 28

How many operator sites does lac operon have?

Answer 28

Three. O1, O2, and O3

Question 29

How do the operator sites of the lac operon work?

Answer 29

The lac repressor must bind to two out of three operators to cause maximal repression. O1 to O2, or O1 to O3, but not O2 to O3.

Question 30

What regulates the trp operon?

Answer 30

A repression protein and attenuation.

Question 31

What does trp operons do?

Answer 31

It encodes enzymes that are necessary for the biosynthesis of the amino acid tryptophan.

Question 32

What is attenuation?

Answer 32

A segment of DNA, termed the attenuator, is necessary for this form of regulation. This mechanism has two features. First, there are two tryptophan codon within the sequence that encode the trp leader peptide. Second, the RNA that is transcribed from this region is able to form stem-loop structures. Different combinations of stem=loop structures are possible.

Question 33

What can the 3/4 loop do?

Answer 33

terminate transcription

Question 34

On what do conditions that favor the formation of the 3/4 loop for trp operon rely on?

Answer 34

Translation of the trpL gene

Question 35

What is the purpose of the 3/4 loop?

Answer 35

It is a transcriptional terminator. It causes RNA polymerase to pause the U-rich sequence dissociate from the DNA.

Question 36

How does 3/4 loop form when there is transcription but no translation?

Answer 36

Region 1 hydrogen bonds to region 2, leaving region 3 to bind to region 4.

Question 37

How does 3/4 loop form when there are high tryptophan levels?

Answer 37

There is sufficient tryptophan in the cell so translation of trpL gene progresses to its stop codon, where the ribosome pauses. The pausing at the stop codon prevents region 2 from h bonding with any region and therefore allows region 3 to h bond to region 4.

Question 38

catabolism

Answer 38

Breakdown of a substance

Question 39

Translational regulation

Answer 39

Regulation of the translation of mRNA

Question 40

Antisense RNA

Answer 40

complementary to an mRNA. It is used to regulate translation. When antisense RNA binds to the mRNA, it prevents translation.

Question 41

What are two common ways to regulate protein function?

Answer 41

Feedback inhibition and altering protein function by covalent modification of their structure

Question 42

Feedback inhibition

Answer 42

Final product in a metabolic pathway often can inhibit an enzyme that acts early in the pathway

Question 43

What kind of modifications are involved with the assembly of a functional protein?

Answer 43

proteolytic processing, disulfide bond formation, attachment of prosthetic groupswm, sugars or lipids. Typically, these changes are irreversible.

Question 44

What kind of protein product modifications are reversible?

Answer 44

Phosphorylation (-PO4), acetylation, (-COCH3), and methylation (-CH3)