Chapter 16, Control of Gene Expression in Bacteria Video Solutions, Genetics: A Conceptual Approach

01:22

Problem 1

Why is gene regulation important for bacterial cells?

Dennis Howard

Numerade Educator

01:58

Problem 2

Name six different levels at which gene expression might be controlled.

Dennis Howard

Numerade Educator

03:17

Problem 3

Draw a picture illustrating the general structure of an operon and identify its parts.

Dennis Howard

Numerade Educator

03:19

Problem 4

What is the difference between positive and negative control? What is the difference between inducible and repressible operons?

Dennis Howard

Numerade Educator

05:49

Problem 5

Briefly describe the lac operon and how it controls the metabolism of lactose.

Dennis Howard

Numerade Educator

02:54

Problem 6

What is catabolite repression? How does it allow a bacterial cell to use glucose in preference to other sugars?

Dennis Howard

Numerade Educator

03:05

Problem 7

What is attenuation? What are the mechanisms by which the attenuator forms when tryptophan levels are high and the antiterminator forms when tryptophan levels are low?

Dennis Howard

Numerade Educator

02:37

Problem 8

What is antisense RNA? How does it control gene expression?

Dennis Howard

Numerade Educator

02:05

Problem 9

What are riboswitches? How do they control gene expression? How do riboswitches differ from RNA-mediated repression?

Dennis Howard

Numerade Educator

02:20

Problem 10

Examine Figure $16.2 \mathrm{b}$. Why do you think the motif of the DNA-binding protein shown is called a zinc-finger motif?

Dennis Howard

Numerade Educator

02:03

For each of the following types of transcriptional control, indicate whether the protein produced by the regulator gene will be synthesized initially as an active repressor or as an inactive repressor.
a. Negative control in a repressible operon
b. Negative control in an inducible operon

Dennis Howard

Numerade Educator

05:00

Problem 12

A mutation at the operator prevents the regulator protein from binding.
What effect will this mutation have in the following types of operons?
a. Regulator protein is a repressor of a repressible operon.
b. Regulator protein is a repressor of an inducible operon.

Matt Borglin

Numerade Educator

02:22

Problem 13

The blob operon produces enzymes that convert compound A into compound B. The operon is controlled by regulator gene $S .$ Normally, the enzymes are synthesized only in the absence of compound B. If gene $S$ is mutated, the enzymes are synthesized in the presence and in the absence of compound B. Does gene $S$ produce a regulator protein that exhibits positive or negative control? Is this operon inducible or repressible?

Dennis Howard

Numerade Educator

01:56

Problem 14

A mutation prevents the catabolite activator protein (CAP) from binding to the promoter in the lac operon. What will the effect of this mutation be on the transcription of the operon?

Dennis Howard

Numerade Educator

01:58

Problem 15

Transformation is a process in which bacteria take up new DNA released by dead cells and integrate it into their own genomes (see p.
265 in Chapter 9 ). In Streptococcus pneumoniae (which causes many cases of pneumonia, inner-ear infections, and meningitis), the ability to carry out transformation requires from 105 to 124 genes, collectively termed the com regulon. The com regulon is activated in response to a protein called competence-stimulating peptide (CSP), which is produced by the bacteria and exported into the surrounding medium. When enough CSP accumulates, it attaches to a receptor on the bacterial cell membrane, which then activates a regulator protein that stimulates the transcription of genes within the com regulon and sets in motion a series of reactions that ultimately result in transformation. Does the com regulon in Streptococcus pneumoniae exhibit positive or negative control? Explain your answer.

Dennis Howard

Numerade Educator

04:08

Problem 16

Under which of the following conditions would a lac operon produce the greatest amount of $\beta$ -galactosidase? The least? Explain your reasoning.
$$\begin{array}{lcr}
& \text { Lactose present } & \text { Glucose } \mathbf{p} \\
\text { Condition 1 } & \text { Yes } & \text { No } \\
\text { Condition 2 } & \text { No } & \text { Yes } \\
\text { Condition 3 } & \text { Yes } & \text { Yes } \\
\text { Condition 4 } & \text { No } & \text { No }
\end{array}$$

Dennis Howard

Numerade Educator

02:59

Problem 17

A mutant strain of $E .$ coli produces $\beta$ -galactosidase in both the presence and the absence of lactose. Where in the operon might the mutation in this strain be located?

Dennis Howard

Numerade Educator

02:01

Problem 18

Examine Figure $16.7 .$ What would be the effect of a drug that altered the structure of allolactose so that it was unable to bind to the regulator protein?

Dennis Howard

Numerade Educator

01:52

Problem 19

For $E .$ coli strains with the lac genotypes shown below, use a plus sign
(+) to indicate the synthesis of $\beta$ -galactosidase and permease and a minus sign (-) to indicate no synthesis of the proteins.

Rabeya Zahid

Numerade Educator

04:43

Problem 20

Give all possible genotypes of a lac operon that produces, or fails to produce, $\beta$ -galactosidase and permease under the following conditions. Do not give partial-diploid genotypes.

Dennis Howard

Numerade Educator

02:40

Problem 21

Explain why mutations in the lacI gene are trans in their effects, but mutations in the lacO gene are cis in their effects.

Dennis Howard

Numerade Educator

01:47

Problem 22

Which strand of DNA (upper or lower) in Figure 16.8 is the template strand? Explain your reasoning.

Dennis Howard

Numerade Educator

03:01

Problem 23

The $m m m$ operon, which has sequences $A, B, C,$ and $D$ (which may be structural genes or regulatory sequences), encodes enzymes 1 and 2 . Mutations in sequences $A, B, C,$ and $D$ have the following effects, where
a plus $\operatorname{sign}(+)$ indicates that the enzyme is synthesized and a minus sign
$(-)$ indicates that the enzyme is not synthesized.
a. Is the $m m m$ operon inducible or repressible?
b. Indicate which sequence $(A, B, C, \text { or } D)$ is part of the following components of the operon:
Regulator gene ____________
Promoter ____________
Structural gene for enzyme 1 __________
Structural gene for enzyme 2 ____________

Dennis Howard

Numerade Educator

03:46

Problem 24

. Ellis Engelsberg and his colleagues examined the regulation of genes
taking part in the metabolism of arabinose, a sugar (E. Engelsberg et al.
1965. Journal of Bacteriology $90: 946-957$ ). Four structural genes encode enzymes that help metabolize arabinose (genes $A, B, D,$ and $E$ ). An additional sequence $C$ is linked to genes $A, B,$ and $D .$ These are in the order $D-A-B-C .$ Gene $E$ is distant from the other genes. Engelsberg and his colleagues isolated mutations at the $C$ sequence that affected the expression of structural genes $A, B, D,$ and $E .$ In one set of experiments, they created various genotypes at $A$ and $C$ and determined whether arabinose isomerase (the enzyme encoded by gene $A$ ) was produced in the presence or absence of arabinose (the substrate of arabinose isomerase) by cells with these genotypes. Results from this experiment are shown in the following table, where a plus sign ( $+$ ) indicates that the arabinose isomerase was synthesized and a minus sign ( $-$ ) indicates that the enzyme was not synthesized.
a. On the basis of these results, is the $C$ sequence an operator or a regulator gene? Explain your reasoning.
b. Do these experiments suggest that the arabinose operon is negatively or positively controlled? Explain your reasoning.
c. What type of mutation is $C^{\mathrm{c}} ?$

Dennis Howard

Numerade Educator

06:20

Problem 25

.In $E .$ coli, three structural genes $(A, D, \text { and } E)$ encode enzymes $\mathrm{A}, \mathrm{D}$
and $\mathrm{E}$, respectively. Sequence $O$ is an operator. The sequences are in the order $O-A-D-E$ on the chromosome. The three enzymes encoded by $A$
$D,$ and $E$ catalyze the biosynthesis of valine. Mutations at the $A, D, E$ and $O$ were isolated to study the production of enzymes $A, D,$ and $E$ when cellular levels of valine were low (T. Ramakrishnan and E. A. Adelberg. $1965 .$ Journal of Bacteriology $89: 654-660$ ). Amounts of the enzymes produced by partial-diploid $E .$ coli with various combinations of mutations are shown in the following table.
a. Is the regulator protein that binds to the operator of this operon a repressor (negative control) or an activator (positive control)? Explain your reasoning.
b. Are genes $A, D,$ and $E$ all under the control of operator $O ?$ Explain your reasoning.
c. Propose an explanation for the small amount of enzyme $\mathrm{E}$ produced by genotype $3 .$

Niamat Khuda

Numerade Educator

02:42

Problem 26

At which level of gene regulation shown in Figure 16.1 does attenuation Occur?

Dennis Howard

Numerade Educator

05:26

Problem 27

Listed in parts $a$ through $g$ are some mutations that were found in the $5^{\prime}$ UTR of the trp operon of $E .$ coli. What will the most likely effect of each of these mutations be on the transcription of the trp structural genes?
a. A mutation that prevents the binding of the ribosome to the $5^{\prime}$ end of the mRNA $5^{\prime}$ UTR
b. A mutation that changes the Trp codons in region 1 of the mRNA $5^{\prime}$ UTR into codons for alanine
c. A mutation that creates a stop codon early in region 1 of the mRNA $5^{\prime}$ UTR
d. Deletions in region 2 of the mRNA $5^{\prime}$ UTR
e. Deletions in region 3 of the mRNA $5^{\prime}$ UTR
f. Deletions in region 4 of the mRNA $5^{\prime}$ UTR
g. Deletion of the string of adenine nucleotides that follows region 4 in the
$\overline{5}^{\prime}$ UTR

Dennis Howard

Numerade Educator

01:50

Problem 28

Some mutations in the $\operatorname{tr} p$ 5' UTR increase termination by the attenuator. Where might these mutations occur, and how might they affect the

Dennis Howard

Numerade Educator

02:12

Problem 29

Some of the mutations of the type mentioned in Problem 28 have an interesting property: they prevent the formation of the antiterminator that normally takes place when the tryptophan level is low. In one of these mutations, the AUG start codon for translation of the $5^{\prime}$ UTR has been deleted. How might this mutation prevent antitermination from taking place?

Dennis Howard

Numerade Educator

02:10

Problem 30

Several examples of antisense RNA regulating translation in bacterial cells have been discovered. Molecular geneticists have also used antisense RNA to artificially control transcription in both bacterial and eukaryotic genes. If you wanted to inhibit the transcription of a bacterial gene with antisense RNA, what sequences might the antisense RNA contain?

Dennis Howard

Numerade Educator

01:42

Problem 31

Would you expect to see attenuation in the lac operon and other operons that control the metabolism of sugars? Why or why not?

Dennis Howard

Numerade Educator

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