Prokaryotic Gene Regulation. Flashcards
1
Q
Define activator proteins?
A
Proteins that will bind to the operator region and allow RNA polymerase to bind to the promoter.
2
Q
Define allolactose?
A
An isomer of lactose.
3
Q
Define constitutive genes?
A
Genes that are expressed all of the time.
4
Q
What are constitutive genes also known as?
A
Housekeeping genes.
5
Q
Define co-ordinated gene expression?
A
When several genes are controlled by one regulator.
6
Q
Define enzyme induction?
A
The up-regulation of gene expression for the production of a certain enzyme.
7
Q
What will be the results of enzyme induction?
A
The formation of more enzymes.
8
Q
Define inducible enzymes?
A
Enzymes that are made when they are needed.
9
Q
Inducible enzymes are made by what kind of genes?
A
By regulated genes that are turned on.
10
Q
Define negative regulation?
A
The process that leads to the production of a repressor proteins which will turn off an operon.
11
Q
Define an operator region?
A
A region of a bacterial gene, where proteins that help with the expression of this gene will bind to.
12
Q
Define an operon?
A
A cluster of genes that are involved in similar processes and can be activated by a single polycistronic mRNA.
13
Q
Define a plasmid?
A
A piece of extrachromosomal DNA that is found in plasmids.
14
Q
Define the promoter region?
A
The upstream region of a gene where RNA polymerase will bind to.
15
Q
Define regulated genes?
A
Genes that are expressed some of the time.
16
Q
Define repressor proteins?
A
Proteins that bind to the operator region and prevent RNA polymerase from binding to the promoter.
17
Q
Define transcriptional control?
A
A method of controlling the transcription of genes on an operon.
This will control how much mRNA is made from this operon by RNA polymerase.
18
Q
Define translational control?
A
The regulation of translation or protein synthesis by pre-formed mRNA’s.
19
Q
What are 2 examples of processes that are controlled by gene regulation?
A
Many of the genetic functions such as transcrition and translation.
20
Q
Can prokaryotes carry out transcription and translation at the same time?
A
Yes.
21
Q
Why can prokaryotes carry out transcription and translation at the same time?
A
Because both processes occur in the cytoplasm allowing the ribosomes to receive the mRNA as it is produced.
22
Q
What are plasmids?
A
Extrachromosomal pieces of DNA that is found in prokaryotes.
23
Q
Why will bacteria shut down many non-essential genes?
A
In an effort to save energy.
24
Q
When will bacteria express the LAC operon?
A
When lactose is the only available glucose source.
25
What happens if bacteria use energy by unnecessarily expressing genes?
Their division time will increase and they could be out competed by other strains of bacteria.
26
What kind of gene is always expressed within the cell?
Constitutive genes.
27
What is the opposite of a constitutive gene?
A regulated gene.
28
When is a regulated gene expressed?
When it is turned on.
29
What kind of genes are not energy efficient?
Constitutive genes.
30
What kind of tasks are constitutive genes used for in prokaryotes?
In critical processes such as the regulation of metabolism.
31
Why must constitutive genes constantly be synthesising new proteins?
Because proteins have certain lifespans and at the end of these lifespans they will be degraded.
32
When will regulated genes synthesise proteins?
Under certain conditions.
33
Will regulated genes make proteins in high or low numbers?
In very low numbers, unless enzymatic induction occurs and more enzymes need to be synthesised.
34
What kind of genes will control their sugar metabolism?
Regulated genes.
35
What enzyme will convert lactose to glucose and galactose?
The beta-galactosidase enzyme.
36
Can gene regulation take place during transcription, mRNA processing or translation?
Yes.
37
Where is the operator region of an operon located, relative to the start sequence?
Downstream from the bacterial start codon.
38
What is the job of the operator region of an operon?
It is the binding site for regulatory proteins bind which will regulate whether the gene is transcribed or not.
39
What does the operator region lie next to in an operon?
The operator region lies next to the promoter region.
40
What is the job of the promoter region in an operon?
It is where RNA polymerase will bind to when the gene needs to be transcribed.
41
Can an operator region control the transcription of multiple genes?
Yes.
E.g. In an operon.
42
What are the 2 types of regulator protein that can bind to the operator region of an operon?
Repressor proteins.
Activator proteins.
43
Where will a repressor protein bind to on an operon?
To the operator.
44
How does the binding of a repressor protein to the operator region affect the operon?
It will prevent RNA polymerase from binding to the promoter meaning the gene cannot be transcribed.
45
How do activator proteins affect an operon?
They cause the repressor to detach from the operator.
This allows RNA polymerase to attach to the promote and for transcription to occur.
46
What are the 3 genes found in the LAC operon?
LAC-Z.
LAC-Y.
LAC-A.
47
Who discovered the LAC operon?
Jacob and Monod.
48
What is lactose made up from?
A glucose molecule that has bound to a galactose molecule.
49
What enzyme is responsible for breaking down lactose in E.coli?
The beta galactosidase enzyme breaks lactose down into its constituent parts.
50
What is the isomer of lactose?
Allolactose.
51
Can beta galactosidase convert lactose to allolactose?
Yes.
52
How are the structural genes arranged in the LAC operon?
The LAC-Z, LAC-Y and LAC-A genes are adjacent to each other.
53
When are the LAC genes expressed?
When the bacterial cell is placed in lactose and glucose levels are low.
54
What kind of mRNA can activate all 3 LAC genes?
A polycistronic piece of mRNA.
55
What is the job of the LAC-Z gene?
It codes for beta-galactosidase which will break down lactose.
56
What is the job of the LAC-Y gene?
It codes for the permease enzyme which helps to transport lactose across the cell membrane.
57
What is the job of the LAC-A gene?
It codes for the transacetylase enzyme which will acetylate galactose, changing it to acetyl-galactose.
58
How many promoters control the 3 genes on the LAC operon?
A single promoter.
59
What is the promoter on the LAC operon called?
LAC-P.
60
What is the operator on the LAC operon called?
LAC-O.
61
Is there any DNA between the operator and the start codon?
A leader sequence of non coding RNA is found between the operator and the 1st gene on the LAC operon.
62
What gene on the LAC operon can be found upstream of the promoter?
The LAC-I gene.
63
What is the job of the LAC-I gene on the LAC operon?
It will produce the repressor protein when the cell is not in a lactose environment.
64
What is the order of genes from upstream to downstream on the LAC operon?
LAC-I.
Promoter.
Operator.
Leader sequence.
LAC-Z.
LAC-Y.
LAC-A.
65
What will the LAC operons repressor protein do when the cell is not in a lactose environment?
It binds to the operator region and will stop the LAC genes from being transcribed.
66
What will induce the LAC operon?
If the bacterial cell finds itself in a solution containing lactose, then it will be induced or turned on.
67
How does lactose turn the LAC operon on?
Lactose enters the cell and binds to the LAC-operon.
This will induce a conformational change that causes the repressor to fall off.
68
When a cell is in a lactose environment, what will stop the repressor from re-binding to the operator?
Allolactose which as an inducer ands binds to the active site of the repressor.
69
When the repressor is removed from the LAC operon, what can take its place?
RNA polymerase II.
70
What will happen when RNA polymerase binds to the LAC operon when the repressor has been removed?
It will transcribe the 3 LAC genes allowing lactose to be metabolised.
71
What will happen to the LAC operon if a cell is removed from a lactose environment?
The repressor will come back and bind to the operator blocking RNA polymerase from binding.
72
Mutations in the LAC operon will affect which processes?
Transcription and translation.
73
What is the LAC I- mutation?
A mutation in the LAC-I gene which produces the repressor protein.
It creates a non-functional repressor and transcription of the LAC genes cannot be turned off.
74
What is the LAC IS mutation?
It affects the LAC-I gene.
It leads to the production of a super repressor that cannot be removed even when the cell is in lactose.
75
What is the LAC OC mutation?
It affects the LAC-O gene.
It leads to a non-functional operator which meant that the repressor protein cannot bind to the operator.
This causes the LAC gene to become a constitutive gene.
76
What are the LAC Z-, LAC Y- and LAC A- mutations?
Mutations in these genes result in the production of faulty proteins which will affect how lactose is metabolised.
77
What is the LAC P- mutation?
It affects the LAC-P gene and results in a faulty promoter region.
This affects the binding of RNA polymerase, meaning that transcription can't take place.
78
What is the favourite carbon source of e.coli bacteria?
Glucose.
79
What will e.coli metabolise if they are placed in a solution of glucose and lactose?
They will only metabolise glucose.
80
Will the LAC operon be expressed in the presence of glucose?
No.
81
What is the hunger signal is e.coli?
cAMP (cyclic AMP).
82
What will the expression of cAMP do inside an e.coli cell?
It allows for the expression of genes that break down sugars such as glucose and lactose.
83
What protein will cAMP bind to and activate when glucose levels are low in e.coli?
The catabolite gene activator protein (CAP).
Which is also known as the cAMP regulatory protein (CRP).
84
What will the CAP protein do when it is activated by cAMP?
The CAP protein will bind to LAC-P and will help to activate transcription.
85
What levels will increase in e.coli if glucose levels fall?
If glucose concentrations decline then cAMP levels will increase and this will activate genes that produce glucose.
86
What will happen to the promoter region of the LAC operon when the Camp/CAP complex binds to it?
It will cause a conformational change in the DNA which allows RNA polymerase to bind to the operon.
87
When will the CAMP-CAP complex bind to the LAC operon?
When intracellular glucose levels are low and the only available glucose source is lactose.
88
cAMP is involved in what kind of regulation of the LAC operon?
In the positive regulation of the LAC operon and can be thought of as an activator protein.
89
What molecule will inhibit adenylate cyclase in e.coli?
The presence of glucose will inhibit the production of adenylate cyclase.
90
What enzyme will produce cAMP?
Adenylate cyclase.
91
If intracellular glucose is high, will adenylate cyclase be produced?
No.
This also means that cAMP will not be produced and the CAMP-CAP complex cannot be formed.
92
When is glucose a positive regulator of the LAC operon?
When glucose levels are low.
93
When is glucose a negative regulator of the LAC operon?
When glucose levels are high.
94
What will be produced by the TRP operon?
It will produce the components necessary to produce tryptophan.
95
What will inhibit the TRP operon from working?
It relies on feedback inhibition, meaning that it is inhibited by its own product.
96
If tryptophan is in high concentrations, will the TRP operon be working?
No.
97
If tryptophan is in very low concentrations, will the TRP operon be working?
Yes.
98
What proteins will the activation of the TRP operon lead to?
The enzymes that will synthesise tryptophan.
99
When will a repressor protein bind to the TRP operon?
When tryptophan levels are high.
100
When will the repressor fall off the TRP operon?
When tryptophan levels are low.
101
What gene codes for the repressor on the TRP operon?
The TRPr gene.
102
Where is the TRPr gene located on the the TRP operon?
It is located far away from the TRP operon.
103
What co-repressor will control the binding of the repressor protein to the TRP operon?
A tryptophan molecule. which acts as a co-repressor,.
104
How does tryptophan act as a co-repressor for the TRP operon?
It forms a bond with the repressor protein and this tryptophan/protein complex will then bind to the operator.
105
How will the presence of no tryptophan affect the TRP repressor?
The repressor protein is stopped from binding to the operator and this allows RNA polymerase to bind instead.
106
What are the 5 types of genes that make up the TRP operon?
Operator region (TRP-O).
Promoter region (TRP-P).
5 Protein coding genes (TRP-E, TRP-D, TRP-C, TRP-B and TPR-A).
Repressor protein (TRP-R).
Leader sequence (TRP-L).
107
What is the TRP-O gene?
It is where the repressor will bind to when tryptophan is not needed.
108
What is the TRP-P gene?
It is the promoter region, where RNA polymerase will bind to when the TRP genes need to be transcribed.
109
What are the Protein coding genes (TRP-E, TRP-D, TRP-C, TRP-B and TPR-A) on the TRP operon?
These are the genes that will code for the proteins that will make tryptophan.
110
What is the TRP-R gene?
It codes for the repressor protein and it prevents transcription when tryptophan levels are high.
This gene is located far away from the TRP operon.
111
What is the TRP-L gene?
The leader sequence on the TRP operon lies between the promoter and the start codon.
112
Will the TRP-L gene (leader sequence) of the TRP operon code for any proteins?
Yes.
113
What are the 2 regions found within the leader sequence on the TRP operon?
It contains a ribosomal binding site which is made up of multiple TRP codons.
It contains a region called the attenuator which will fold into 1 of 2 RNA structures.
114
How will attenuation affect the TRP operon?
Its is another method that is used to control translation within the TRP-operon.
115
What is the first protein coding region of the TRP operon?
The TRP-L gene.
It is located upstream of the 5 structural genes and it contains 2 different codons for tryptophan.
116
How many different sections does the TRP-L mRNA have?
It contains 4 different sections that can form hairpin loops via the formation of complimentary bonds.
117
What is the most stable form of TRP-L mRNA?
When the 1st loop is created when regions 1 and 2 form bonds with each other and when regions 3 and 4 form bonds.
This creates 2 hairpin loops.
118
Are there any special features that are particular to any of the 4 sequences of mRNA in TRP-L mRNA?
At the end of the 2nd loop (section 4) is a sequence of U’s which act as a stop codon for RNA polymerase.
The 2 TRP codons are located in section 1 and there is a ribosomal stop codon at the end of section 1.
119
What 2 main things affect attenuation of the TRP-L gene?
The levels of intracellular tryptophan and the positioning of the ribosome on the mRNA.
120
Attenuation is what form of control?
Translational control.
121
Will the mRNA from the TRP operon be transcribed and translated at the same time?
Yes.
It is prokaryotic mRNA.
122
What 7 steps occur when the ribosome reaches the TRP codons on the TRP-L gene when intracellular tryptophan levels are high?
The ribosome will reach the TRP codons on section 1.
Loaded tRNA will deliver tryptophan amino acids and the ribosome can add them to the polypeptide.
The ribosome will then stop at the stop codon beyond section 1 and will fall off the mRNA strand.
This allows sections 1 and 2 and sections 3 and 4 to form complimentary bonds.
This causes the RNA polymerase to reach the stop sequence of U’s at the end of section 4.
The stop sequence prompts the polymerase to fall off the DNA.
This results in the stopping transcription and translation.
123
Why will the DNA for the structural proteins not be transcribed in the TRP operon if the ribosome can make tryptophan on the leader sequence?
Because tryptophan is present meaning that the proteins required to make tryptophan do not need to be made.
124
What 6 steps occur when the ribosome reaches the TRP codons on the TRP-L gene when intracellular tryptophan levels are low?
The ribosome reaches the TRP codons on section 1.
Low levels of intracellular tryptophan mean that the tRNA cannot bring the amino acid.
This causes the ribosome to pause at the TRP codons.
The presence of the ribosome on section 1 allows section 2 and section 3 of the TRP-L mRNA to form bonds.
The bonding of sections 2 and 3 prevents the formation of the stop codon for RNA polymerase.
RNA polymerase goes on to code for the structural genes and the proteins that will make tryptophan are made.
