Chapter 16 - Control of Gene Expression in Prokaryotes

Question 1

A(n) __________ operon is normally turned on, and it is turned off by a(n) _________.

Answer 1

repressible; repressor

Question 2

For a(n) __________ operon, transcription normally does NOT take place, and it is kept off by a(n) _________.

Answer 2

Inducible; repressor

Question 3

The lac operon is an example of a __ __ genetic system because the binding of the lac __ to the operator inhibits transcription by RNA polymerase.

Answer 3

negative inducible; repressor

Question 4

Low levels of glucose lead to all of the following except:
A. cAMP levels increase
B. permease levels increase
C. β-galactosidase levels increase
D. the lac operon is activated
E. CAP-cAMP loses its affinity for DNA

Answer 4

E. CAP-cAMP loses its affinity for DNA

Question 5

A critical part of gene regulation requires __ proteins which have binding __. Commonly found within __ are __: simple proteins structures that include__-loop-__, __ fingers, and __ zipper.

Answer 5

regulatory; domains

domains; motifs; helix-loop-helix; zinc; leucine

Question 6

Regulatory protein motifs: describe a helix-turn-helix.

Answer 6

Two 𝜶-helices connected by a turn. The helices fit into the grooves of DNA.

Question 7

Regulatory protein motifs: describe zinc fingers

Answer 7

Finger-shaped loops of AAs associated with a zinc ion. The fingers fit into the major groove of DNA.

Question 8

Regulatory protein motifs: describe leucine zippers.

Answer 8

Helix of leucine residues and an arm of basic AAs that bind to two adjacent major grooves.

Question 9

How do amino acids in DNA-binding proteins interact with DNA?

a. By forming covalent bonds with DNA bases
b. By forming hydrogen bonds with DNA bases
c. By forming covalent bonds with DNA sugars

Answer 9

b. By forming hydrogen bonds with DNA bases

Question 10

In bacteria, genes with related functions, called __, are clustered together and often transcribed into a ___ mRNA. They are regulated by a __ gene that is not part of the ___.

Answer 10

operons, single

regulatory; operon

Question 11

Operons are regulated by ___ ___. They function by binding to the ___ (part of the operon) and either __ or __ transcription.

Answer 11

regulatory proteins.

operator; induce; repress

Question 12

In negative inducible operons, the regulatory protein is a __ and __ transcription. The regulatory protein is made in __ form.

Because the operon is inducible, transcription requires an ___ to bind to and __ the regulatory protein (the __ causes an __ change in the regulatory protein). Note: precursor to the final product is usually the ____.

Answer 12

repressor; blocks
active

inducer; inactivate; inducer; allosteric

inducer

Question 13

In negative repressible operons, the regulatory protein is a __ and __ transcription. The regulatory protein is normally ___ until a ___ binds to it; once this occurs, the regulatory protein binds to and __ transcription (binding of the ___ causes ___ changes that activate the regulatory protein). Note: the product usually serves as the ___.

Answer 13

repressor; stops.

inactive; corepressor
stops/represses; corepressor; allosteric

corepressor

Question 14

In positive inducible operons, the regulatory protein is made in __ form; it requires an __ to bind to it, which will cause an __ change and promote binding to the __, which will __ transcription. Note: the product precursor usually serves as the ___.

Answer 14

inactive; inducer; allosteric; operator; start/induce

inducer

Question 15

In positive repressible operons, the regulatory protein is usually in ___ form and __ transcription. When a ___ binds to the regulatory protein, ___ changes cause ___ of the protein from the operator, and transcription __. Note: the product usually serves as the ___.

Answer 15

active; promotes

corepressor; allosteric; dissociation; stops/repressed.

corepressor

Question 16

In the 60’s, Jacob and Monad were able to identify and describe the operon model by using what?

Answer 16

classical genetics using mutations to determine how transcription was regulated.

Question 17

E. coli must transport lactose across the membrane to metabolize it. This requires __ (lacY gene product). The disaccharide must be broken down by _-__ (lacZ product). A third gene, LacA, codes for __ __, but nobody knows WTF it does. All 3 genes are structural and are transcribed as a __ mRNA - that makes the mRNA __. The __ protein is made by (lacI). The __ is an element called lacO.

Answer 17

permease

β-galactosidase

thiogalctoside transacetylase

single; polycystronic

regulatory

operator

Question 18

β-galactosidase performs 2 functions; it breaks the bond of __ to yeild __ and __; and it changes the bond to yield ___ (a stereoisomer of lactose).

Answer 18

lactose; galactose; glucose

allolactose

Question 19

In the absence of lactose, the regulatory protein, a __, binds to the operator and __ transcription. Only the presence of lactose can __ transcription. This form of regulation is __ __.

Answer 19

repressor; inhibits/represses.

induce

negative inducible.

Question 20

In the lac operon, the presence of lactose causes __ changes to the regulatory protein (a __) which, in turn, causes ___ of the protein, so transcription is ___. This form of regulation is __ __.

Answer 20

allosteric; repressor; dissociation; induced.

negative inducible.

Question 21

The operator of the lac operon overlaps the __ and the _’ of the __ gene.

Answer 21

promoter; 5’; lacZ

Question 22

___ of the lac operon is __ 100%. The cells __ have low __ of the 3 protein products. When lactose is available, __ transports a small amount, _-__ coverts some of it to __ which acts as the __.

Answer 22

repression; never

always; levels

permease; β-galactosidase; allolactose; inducer

Question 23

Lab work with the lac operon usually uses __ instead of lactose; __ can’t be __.

Answer 23

IPTG; IPTG; metabolized

Question 24

Two levels of regulation for the lac operon are:
(1) __ __: binding of the lac repressor to the operator ___ transcription. (2) __ __ binding of __ __ __ (CAP) stimulates transcription (contingent on glucose levels being __).

Answer 24

negative inducible; blocks

positive inducible; catabolite activator protein; low

Question 25

If glucose is present, metabolism of other sugars by E. coli will be __. This phenomenon is called ___ ___.

Answer 25

repressed.

catabolite repression

Question 26

The positive inducement method of lac regulation includes a __ __ __ (CAP) binding to a sequence that overlaps the __. This causes RNA polymerase to bind to the lac operon much more __ and __ transcription. CAP must form a complex with __ __ before it can bind to DNA (__ __ is often called a second messenger for this reason). The levels of __ __ are __ proportional to glucose levels.

Answer 26

catabolite activator protein; promoter

efficiently; speeds/enhances

cyclic AMP (cAMP); cyclic AMP; cyclic AMP; inversely

Question 27

Little CAP-cyclic AMP forms when there is __ concentration of __; therefore, it does not bind to the lac promoter. Conversely when __ levels are __, CAP-cyclic AMP concentration is high, and it binds to the lac promoter

Answer 27

high; glucose

glucose; low

Question 28

CAP is a __ control on the lac operon, but it also works on at least __ different operons in E. coli. It contains a __-__-__ motif which, when bound, __ the DNA to facilitate unwinding of the ___ so RNA polymerase can initiate transcription. CAP functions as a __ meaning two CAP proteins interact.

Answer 28

positive; 20

helix-loop-helix; bends; promoter

dimer

Question 29

___ is a form of gene regulation that couples transcription and translation only found in ___.

Answer 29

Attenuation; prokaryotes

Question 30

___ functions to slow expression of genes needed for Trp (W) synthesis as Trp levels rise.

Answer 30

Attenuation

Question 31

___ is aka feedback inhibition.

Answer 31

Attenuation