Gene Regulation Flashcards
(127 cards)
1
Q
are clusters of genes under the control of a single promoter, found primarily in prokaryotes
A
operons
2
Q
The
expression of these genes is regulated to allow the organism to respond efficiently to ___
changes.
A
environmental
3
Q
Two key concepts in operon regulation are
A
inducible
constitutive
4
Q
is typically “off” (not transcribed) and can be turned “on”
(induced) when a specific small molecule
A
inducible operon
5
Q
turns on the operon when a specific small molecule is present
A
inducer
6
Q
o In the absence of the inducer, a ___ protein binds tightly to a DNA sequence called
the operator, which is located near the promoter.
A
repressor
7
Q
o In the absence of the inducer, a repressor protein binds tightly to a DNA sequence called
the ___, which is located near the promoter.
A
operator
8
Q
The binding of the repressor physically blocks ___ ____from binding to the
promoter and transcribing the structural genes of the operon.
A
RNA polymerase
9
Q
When the inducer is present, it binds to the repressor protein, causing a ___
change in the repressor.
A
conformational
10
Q
As a result, the ___ is freed, and RNA polymerase can now bind to the promoter
and transcribe the genes of the operon.
A
operator
11
Q
which controls the
metabolism of lactose
A
lac operon
12
Q
isomer of lactose
A
allolactose
13
Q
inducer in lac operon
A
allolactose
14
Q
When
lactose is absent, a ___blocks transcription
A
repressor
15
Q
describes the expression pattern of genes, not a type of operon
model in the same way as “inducible” or “repressible.”
A
constitutive
16
Q
Genes that are ___expressed are transcribed continuously at a relatively
constant level, regardless of environmental conditions.
A
constitutively
17
Q
These genes are often involved in basic
cellular “housekeeping” functions that are always needed for the cell’s survival.
A
constitutively expressed genes
18
Q
While operons are subject to regulation, some genes
within a bacterium (or even entire operons under specific mutant conditions) can be constitutively
expressed if their ___mechanisms are disrupted
A
regulatory
19
Q
. For example, a mutation in the repressor
gene or the operator sequence could lead to the ___being transcribed continuously. However,
this isn’t the “default” state of an inducible or repressible operon; it’s a consequence of altered
regulation.
A
operon
20
Q
is a well-studied system of gene regulation in Escherichia coli (E. coli)
that controls the expression of genes involved in the metabolism of lactose. I
A
lactose operon
21
Q
lac operon is an ___ operon
A
inducible
22
Q
lac operon structures
A
regulatory gene (LacI)
Promoter (P)
operator (O)
structural genes
23
Q
: Located upstream of the operon, this gene codes for the lac repressor
protein.
A
Lac I (regulatory gene)
24
Q
has its own promoter and is constitutively expressed (always “on”),
A
Lac I gene
25
A DNA sequence located at the beginning of the operon
promoter (P)
26
This is the binding site for
RNA polymerase, the enzyme that transcribes DNA into RNA
promoter (P)
27
A DNA sequence that overlaps with or is adjacent to the promoter.
operator (O)
28
This is the
binding site for the lac repressor protein.
operator (O)
29
hese genes are transcribed together as a single messenger RNA (mRNA)
molecule (polycistronic mRNA) and encode enzymes needed for lactose metabolism:
structural genes
30
s a type of mRNA found in prokaryotes (like bacteria) and chloroplasts, that encodes multiple proteins.
polycystronic mRNA
31
Encodes β-galactosidase, an enzyme that hydrolyzes lactose into glucose and
galactose
Lac Z
32
It also converts some lactose into allolactose, the true inducer of the lac
operon.
lac Z
33
Encodes lactose permease,
Lac Y
34
an enzyme that hydrolyzes lactose into glucose and
galactose
B-galactosidase
35
a membrane protein that facilitates the transport of
lactose into the cell.
lactose permease
36
Encodes transacetylase, whose role in lactose metabolism is not fully understood.
lac A
37
, whose role in lactose metabolism is not fully understood.
transacetylase
38
is regulated by the availability of glucose and lactose:
lac operon
39
The lac repressor protein, produced by the lacI gene, binds tightly to the operator (O).
is lactose present?
no
40
This binding physically blocks RNA polymerase from binding to the promoter (P) and
transcribing the structural genes (lacZ, lacY, lacA).
o As a result, the enzymes needed for lactose metabolism are not produced. The operon is
effectively "off".
is lactose present?
no
41
When lactose is present in the environment, it is transported into the cell and converted
into ___by the few β-galactosidase molecules that are present at a very low basal
level.
allolactose
42
When lactose is present in the environment, it is transported into the cell and converted
into allolactose by the few β-galactosidase molecules that are present at a very low ___
level.
basal
43
acts as an inducer. It binds to the lac repressor protein, causing a
conformational (shape) change in the repressor.
allolactose
44
This altered repressor can no longer bind to the operator (O)
is lactose present
yes
45
With the repressor detached, RNA polymerase can now bind to the promoter (P) and
transcribe the lacZ, lacY, and lacA genes.
is lactose present?
yes
46
The enzymes for lactose metabolism are produced, allowing the cell to utilize lactose as a
carbon and energy source. The operon is effectively "on".
is lactose present?
yes
47
E. coli prefers to use ___as its primary energy source.
glucose
48
When glucose is present, the
__ ___ is repressed even if lactose is also available.
lac operon
49
E. coli prefers to use glucose as its primary energy source. When glucose is present, the
lac operon is repressed even if lactose is also available. This is known as
catabolite repression or glucose effect
50
o Glucose levels affect the concentration of
cyclic AMP (cAMP)
51
Low
glucose levels lead to ___cAMP levels,
high
52
___glucose levels lead to low cAMP levels
high
53
cAMP binds to a regulatory protein called
catabolite activator protein (CAP)
54
cAMP binds to a regulatory protein called Catabolite Activator Protein (CAP), forming a
cAMP-CAP complex
55
This complex binds to a specific site upstream of the lac promoter and enhances the
binding of RNA polymerase, thus increasing transcription of the lac operon.
cAMP-CAP complex
56
When glucose levels are high, cAMP levels are low, so ___ ___complex does not form
efficiently
cAMP-CAP complex
57
When glucose levels are high, cAMP levels are low, so cAMP-CAP complex does not form
efficiently. __ ___ binds poorly to the promoter, resulting in low levels of
transcription, even if lactose is present and the repressor is not bound.
RNA polymerase
58
is another crucial system of gene regulation in E. coli, but unlike the
lac operon, it's a repressible operon.
tryptophan operon
59
The tryptophan operon (trp operon) is another crucial system of gene regulation in E. coli, but unlike the
lac operon, it's a
____ operon. T
repressible
60
This means that its transcription is typically "on," and it needs to be
turned "off" in the presence of the corepressor (tryptophan).
repressible operon
61
This means that its transcription is typically "on," and it needs to be
turned "off" in the presence of the ___(tryptophan).
corepressor
62
controls the synthesis of the
amino acid tryptophan, which is essential for the bacterium
trp operon
63
structure of trp operon (5)
regulatory gene
promoter
operator
leader region (trpL)
structural genes
64
Located upstream (but not part of) the trp operon, this gene codes for the
trp repressor protein
trpR
65
is the regulatory gene part of trp operon?
no
66
. The trpR gene has its own promoter and is constitutively expressed,
producing an __repressor.
inactive
67
A DNA sequence at the beginning of the operon. This is the binding site for RNA
polymerase
promoter (P)
68
A DNA sequence that overlaps with the promoter. This is the binding site for the trp
repressor protein when it's active.
operator (O)
69
A short sequence of DNA located between the operator and the first
structural gene (trpE). T
leader region (trpL)
70
The trpL region is transcribed into a leader mRNA that contains a short
coding sequence for a leader peptide and a region called the
attenuator
71
The trpL region is transcribed into a ___ ___ that contains a short
coding sequence for a leader peptide and a region called the attenuator
leader mRNA
72
The trpL region is transcribed into a leader mRNA that contains a short
coding sequence for a ___ ___ and a region called the attenuator
leader peptide
73
This region is crucial for
a second level of regulation called attenuation
leader region (trpL)
74
These five genes are transcribed together as a single polycistronic mRNA and
encode the enzymes needed for tryptophan biosynthesis:
structural genes
75
structural genes of trp operon
trpE
trpD
trpC
trpB
trpA
76
Anthranilate synthase component I
trpE
77
Anthranilate synthase component II
trpD
78
Phosphoribosylanthranilate isomerase and indole-3-glycerolphosphate synthase
trpC
79
Tryptophan synthase β subunit
trpB
80
Tryptophan synthase α subunit
trpA
81
The trp operon is primarily regulated by the availability of __:
tryptophan
82
The trp repressor protein, produced by the trpR gene, is in its inactive form.
level of tryptophan?
low
83
The inactive repressor cannot bind to the operator (O).
RNA polymerase can bind to the promoter (P) and transcribe the entire trp operon (trpE,
trpD, trpC, trpB, trpA).
level of trp?
low tryptophan
84
The enzymes needed for tryptophan synthesis are produced, and the cell can synthesize
its own tryptophan. The operon is effectively "on".
level of trp?
low
85
___acts as a corepressor. When tryptophan levels are high, it binds to the trp
repressor protein, causing a conformational change.
tryptophan
86
Tryptophan acts as a corepressor. When tryptophan levels are ___, it binds to the trp
repressor protein, causing a conformational change.
high
87
This conformational change activates the repressor, allowing it to bind tightly to the
operator (O).
The binding of the active repressor to the operator physically blocks RNA polymerase from
binding to the promoter and transcribing the structural genes.
level of trp?
high
88
The synthesis of tryptophan enzymes is halted, conserving the cell's resources when
tryptophan is readily available. The operon is effectively "of
level of trp?
high
89
The trp operon also employs a unique regulatory mechanism called ___, which provides a finetuned control over transcription.
attenuation
90
The leader mRNA (trpL) contains a ___ ___ ___ ___ (ORF) that encodes a 14-amino acid leader
peptide, which includes two consecutive tryptophan residues
short open reading frame (ORF)
91
The leader mRNA (trpL) contains a short open reading frame (ORF) that encodes a __-amino acid leader
peptide, which includes two consecutive tryptophan residues
14
92
The leader mRNA also has __regions
four
93
The leader mRNA also has four regions (1,
2, 3, and 4) that can form different ___ structures depending on the ribosome's movement during
translation of the leader peptide.
hairpin
94
When tryptophan is abundant, ribosomes quickly translate the leader
peptide. This allows regions 3 and 4 of the leader mRNA to pair, forming a ___ ___
(attenuator)
terminator hairpin
95
When tryptophan is abundant, ___quickly translate the leader
peptide. This allows regions 3 and 4 of the leader mRNA to pair, forming a termination hairpin
(attenuator)
ribosomes
96
When tryptophan is abundant, ribosomes quickly translate the leader
peptide. This allows regions __ and _ of the leader mRNA to pair, forming a termination hairpin
(attenuator)
3 and 4
97
This hairpin signals RNA polymerase to terminate transcription prematurely, before it
reaches the structural genes.
termination hairpin
98
When tryptophan is __, ribosomes stall at the tryptophan codons in
the leader peptide ORF because there isn't enough charged tryptophanyl-tRNA available. T
scarce
99
Low Tryptophan Levels: When tryptophan is scarce, ribosomes stall at the tryptophan codons in
the leader peptide ORF because there isn't enough charged tryptophanyl-tRNA available. This
stalling causes region 2 to pair with region 3, forming an__ ___
anti-termination hairpin
100
Low Tryptophan Levels: When tryptophan is scarce, ribosomes stall at the tryptophan codons in
the leader peptide ORF because there isn't enough charged tryptophanyl-tRNA available. This
stalling causes region __ to pair with region __, forming an anti-termination hairpin
2 and 3
101
This hairpin
prevents the formation of the terminator hairpin (3-4), and RNA polymerase can continue
transcribing the entire trp operon.
anti-termination hairpin
102
Therefore, ___allows for a graded response to tryptophan levels, further reducing transcription
when tryptophan is plentiful and allowing full transcription when it's scarce
attenuation
103
anti-termination hairpin
2-3
104
termination hairpin
3-4
105
DNA of prokaryotes is organized into a __ chromosome, supercoiled within the nucleoid region of the cell cytoplasm
circular
106
DNA of prokaryotes is organized into a circular chromosome, ___within the nucleoid region of the cell cytoplasm
supercoiled
107
DNA of prokaryotes is organized into a circular chromosome, supercoiled within the ___region of the cell cytoplasm
nucleoid
108
proteins that are needed for a specific function or that are involved in the same biochemical pathway are encoded together in blocks called
operons
109
all of the genes needed to use lactose as an energy source are coded next to each other in the ___ operon
lac
110
three types of regulatory molecules that can affect expression of operons
repressors
activators
inducers
111
are proteins produced in the cell
repressors
activators
112
regulate gene expression by binding to specific DNA sites adjacent to the genes they control
repressors and activators
113
activators bind to the ___ site
promoter
114
___ bind to the operator regions
repressors
115
prevent transcription of a gene in response to an external stimulus
activators
116
increase the transcription of a gene in response to an external stimulus
activators
117
are small molecules that may be produced by the cell or that are in the cell's environment
inducers
118
___either activate or repress transcription depending on the needs of the cell and availability of substrate
inducers
119
Controls the metabolism of lactose in Escherichia coli and other bacteria.
lac operon
120
Regulates the synthesis of the amino acid tryptophan in bacteria.
trp operon
121
significance of lac and trop operon
1. Understanding Gene Regulation
These operons serve as model systems for how genes are turned on and off in response to environmental conditions.
The lac operon demonstrates inducible gene expression, helping bacteria adapt to nutrient availability.
The trp operon shows repressible control, conserving energy when tryptophan is abundant.
2. Applications in Biotechnology
The lac operon’s promoter and operator sequences are widely used in genetic engineering to control gene expression in recombinant DNA technology.
Scientists manipulate these systems to regulate protein synthesis in bacterial cultures, such as in insulin production or enzyme manufacturing.
3. Evolutionary Significance
These operons highlight natural selection in microbial populations. Bacteria with efficient gene regulation survive better in changing environments, reinforcing the evolutionary advantages of adaptable gene networks.
Their function demonstrates how organisms optimize metabolic efficiency, a key principle in microbial ecology.
4. Medical and Industrial Relevance
The lac operon helps researchers design antibiotic resistance studies, exploring how bacteria metabolize different sugars.
The trp operon plays a role in amino acid metabolism studies, helping understand tryptophan biosynthesis in engineered bacteria.
122
which of the following E.coli hydrolyze lactose? do they do so constitutively or inducibly (-) means mutation on genes
i p o z
inducible (wild-type) lac operon
repressor is functional
123
which of the following E.coli hydrolyze lactose? do they do so constitutively or inducibly (-) means mutation on genes
i⁻ p o z
→ Constitutive
The repressor is mutated (i⁻) and cannot bind to the operator.
RNA polymerase freely transcribes even in the absence of lactose.
Lactose hydrolysis occurs all the time.
124
which of the following E.coli hydrolyze lactose? do they do so constitutively or inducibly (-) means mutation on genes
i p- o z
faulty
The promoter is mutated (p⁻), preventing RNA polymerase from binding effectively.
No transcription occurs, meaning β-galactosidase is not produced.
Lactose hydrolysis does not occur.
125
which of the following E.coli hydrolyze lactose? do they do so constitutively or inducibly (-) means mutation on genes
i p o- z
i p o⁻ z → Faulty Transcription
The operator is mutated (o⁻), preventing the repressor from binding.
This leads to constitutive transcription (always ON), similar to the i⁻ p o z mutation.
Lactose hydrolysis occurs all the time.
126
for trp operon, describe the operon if the mutations occurs in the following R - P O E D C B A
R⁻ P O E D C B A
Mutation in the repressor (R⁻): The repressor protein is nonfunctional, meaning it cannot bind to tryptophan or the operator.
Effect: The operon is always ON, meaning tryptophan biosynthesis continues even if tryptophan is abundant.
Significance: This leads to wasteful gene expression because the cell produces tryptophan unnecessarily, reducing efficiency.
127
for trp operon, describe the operon if the mutations occurs in the following
R P O E D C- B A
Mutation in the structural gene (C⁻): The enzyme needed for one step in tryptophan synthesis is faulty or missing.
Effect: The operon can still be regulated (turned ON or OFF normally), but tryptophan synthesis is incomplete.
Significance: The cell cannot produce functional tryptophan, leading to a dependence on external tryptophan sources.
