Chapter 16 Genetic Regulation in Bacteria

Which of the following conditions would cause transcription to be activated? (a) A repressor plus an inducer (b) A repressor plus a corepressor (c) An activator plus an inhibitor (d) None of the above

(a) A repressor plus an inducer

The ________ gene encodes a repressor protein. (a) lacA (b) lacI (c) lacZ (d) lacP (e) lacO

(b) lacI

The lac repressor protein binds to the operator and (a) aids RNA polymerase. (b) stops transport of lactose. (c) prevents translation. (d) blocks transcription.

(d) blocks transcription.

A polycistronic mRNA (a) contains the sequences for several genes and control regions. (b) contains the sequences for genes from different operons. (c) contains the sequence for only one gene. (d) contains the sequences of two or more genes.

(d) contains the sequences of two or more genes.

A translational repressor protein binds to: (a) the operator sequence of the DNA (b) the enzyme in an amino acid biosynthetic pathway. (c) an unchanged tRNA. (d) mRNA near the start codon.

(d) mRNA near the start codon.

Monod and Jacob studied lactose metabolism in ________ ________.

E. coli

Answer to 16.5

a

Answers to 16.3

a, b, a

A regulatory protein that increases the rate of transcription is a(n) ________.

activator

Transcription begins but terminates before the entire mRNA is made during ________.

attenuation

Answer to 16.2

b, d, d, d,

Answers to 16.4

d, d

The enzyme beta-galactosidase cleaves the sugar lactose into ________ and ________.

galactose glucose

When the lac repressor binds to the lac ________ site, RNA polymerase cannot transcribe the lacZ, lacY, or lacA genes.

operator

The operon is flanked by a ________ that signals the beginning of transcription and a ________ that signals the end of transcription.

promoter terminator

Experiments by Jacob and Monod demonstrated that enzyme adaptation is due to the regulation of genes during ________.

transcription

In the 1950s, ________, ________, and ________ studied the lac operon in E. coli (select all that apply). (a) Monod (b) Pardee (c) Jacob (d) Chargaff (e) Watson

(a) Monod (b) Pardee (c) Jacob

The lac repressor is composed of how many identical subunits? (a) 2 (b) 3 (c) 4 (d) 1

(c) 4

The binding of ________ to the lac repressor promotes a conformational change that prevents the repressor from binding to the lac operator. (a) lactose (b) β-galactosidase (c) lac permease (d) allolactose

(d) allolactose

True or false: Gene regulation is constant.

False

True or false: On a regulator protein, an allosteric site is the same as the active site.

False

constitutive genes

have constant levels of expression in all conditions over time. The proteins encoded from the genes are continuously needed for the survival of the bacterium

When four molecules of allolactose are bound to the lac repressor, the repressor can no longer bind to the operator site, and RNA polymerase is free to transcribe the structural genes of the operon, the operon has been ________.

induced

The product of an operon may act as a(n) ________ if the operon is repressible.

inhibitor

The three protein-encoding genes in the lac operon are ________, ________, and ________.

lacY lacA lacZ

The exposure of bacterial cells to ________ increases the levels of lactose-utilizing enzymes 100- to 10,000-fold.

lactose

gene regulation

the phenomenon in which the level of gene expression can vary under different conditions

Anabolic enzymes are usually encoded by ________ operons, and ________ operons usually encode catabolic enzymes. (a) repressible; inducible (b) inducible, repressible

(a) repressible; inducible

Select the genes in the *trp* operon (select all that apply). (a) trpB (b) trpA (c) trpC (d) trpY (e) trpZ (f) trpE (g) trpD

(a) trpB (b) trpA (c) trpC (f) trpE (g) trpD

The small effector molecule ________ prevents the lac repressor from binding to the operator site.

allolactose

An enzyme can contain two sites: a catalytic site, and a regulatory or ________ site.

allosteric

The somewhat imprecise term that describes how transcriptional regulation is influenced by glucose is ________ ________.

catabolite repression

Antisense RNA is an RNA strand that is ________ to an mRNA molecule.

complementary

The lacY encode lactose ________, a membrane protein.

permease

The term ________ regulation refers to control of proteins already present in the cell.

posttranslational

The lacA gene encodes galactoside transacetylase, an enzyme that covalently modifies (a) lactose permease. (b) lactose. (c) beta-galactosidase. (d) CAP.

(b) lactose.

Mutations in the gene for lac repressor that result in a lac repressor that cannot bind DNA would mean that transcription from the lac operon is (a) induced or repressed normally. (b) not repressible. (c) always repressed.

(b) not repressible.

The research of Jacob and Monod provided (a) our understanding of the process of translation. (b) our initial understanding of gene regulation. (c) our initial understanding of how transformation occurs. (d) the details pertaining to the structure of DNA. (e) understanding of the process of DNA replication.

(b) our initial understanding of gene regulation.

The CAP site and the operator site are ________ that function in gene regulation. (a) disaccharides (b) short DNA segments (c) large proteins (d) regulatory RNAs

(b) short DNA segments

Riboswitches can regulate (select all that apply) (a) DNA replication (b) splicing (c) transcription (d) RNA stability (e) translation

(b) splicing (c) transcription (d) RNA stability (e) translation

An operon is a group of two or more genes under the transcriptional control of (a) different polymerases. (b) two or more promoters. (c) a single promoter.

(c) a single promoter.

Unregulated genes have (a) constant variable levels of expression depending on the gene. (b) variable levels of expression. (c) constant levels of expression.

(c) constant levels of expression.

What types of genes encode proteins the bacterial cell needs all the time? (a) riboswitches (b) activator genes (c) constitutive genes (d) repressor genes

(c) constitutive genes

An inducer is a small effector molecule that causes transcription to: (a) decrease (b) remain constant (c) increase

(c) increase

In feedback inhibition, the final product in a metabolic pathway: (a) prevents translation of its own mRNA. (b) causes increased production of enzymes that act early in the pathway. (c) inhibits an enzyme that acts early in the pathway. (d) causes the formation of a stem-loop structure in the mRNA that prevents translation.

(c) inhibits an enzyme that acts early in the pathway.

Select all of the following that are protein-encoding genes in the *lac* operon (select all that apply). (a) lacX (b) lacO (c) lacY (d) lacA (e) lacZ

(c) lacY (d) lacA (e) lacZ

Constitutive genes encode (a) proteins the cell needs occasionally. (b) proteins the cell needs when certain nutrients are in the environment. (c) protein the cell needs all the time. (d) proteins the cell needs to make amino acids.

(c) protein the cell needs all the time.

A repressor is a ________ that ________ transcription. (a) small effector molecule; inhibits (b) small effector molecule; enhances (c) regulatory protein; inhibits (d) regulatory protein; enhances

(c) regulatory protein; inhibits

Enzyme adaptation refers to the observation that (a) an enzyme must be present in a cell prior to the cell being exposed to the substrate for that enzyme. (b) enzymes are always presents in cells regardless of whether a substrate is present or absent. (c) a particular substrate appears within a cell only after the cell has been exposed to the enzyme for that substrate. (d) a particular enzyme appears within a cell only after the cell only after the cell has been exposed to the substrate for that enzyme.

(d) a particular enzyme appears within a cell only after the cell only after the cell has been exposed to the substrate for that enzyme.