Topic 5: regulation of gene expression Flashcards
1
Q
How does bacteria regulate metabolic pathways?
A
1) Regulation of enzyme activity by feedback inhibition = allosteric regulation
2) Regulation of enzyme production by gene expression regulation = controlled by operons
2
Q
Describe the operon
A
- Prokaryotic DNA segment = operator + promoter + group of functional related genes
- Works as regulatory = on/off switch controlling cluster of functional genes
- Specific sequence within promoter of genes
3
Q
Define negative gene regulation
A
- Operons switched off by active form of repressors
1) Repressible operons
2) Inducible operons
4
Q
Describe repressible operons
A
- Usually active
- Regulates gene expression = enzymes involved in anabolic pathways
- Synthesis repressed by high level of end product = activates repressor
- E.g. trp operon
5
Q
Describe inducible operon
A
- Inactive
- Regylates gene expression = enzymes involved in catabolic pathways
- Synthesis induced by chemical signal = inactivates repressor
- E.g. lac operon
6
Q
Explain the trp operon
A
- Genes of enzyme involved in tryptophan synthesis
- Repressible operon = transcription normally on = inhibited when trp binds to allosteric on regulatory protein = activates = repressor then binds to operator
7
Q
Describe positive gene regulation
A
- Operons switched on + active form of activator
- Activator = stimulatory protein = catabolite activator protein = enhances lac operon
8
Q
Describe positive gene regulation in glucose levels
A
LOW:
- Increase in level of cAMP
- CAP activated binding to cAMP
- Activated CAP attaches to promoter of lac operon = increases affinity of RNA polymerase + accelerates transcription of lac operon
HIGH:
- Decrease in level of cAMP
- CAP detaches from lac
- Decreased affinity of RNA polymerase = decreased transcription of lac operons
9
Q
Describe gene expression in eukaryotes
A
- Regulates development
- Responsible for cell specialization
10
Q
Define differential gene expression
A
- Expression of different genes by cells with same genome = different cell types produced
11
Q
How much genes of a human cell are expressed at a given time?
A
20%
12
Q
How much of DNA codes for proteins?
A
- 1.5%
- Rest codes for RNA products + NOT transcribed
13
Q
What is euchromatin?
A
- Active form of chromatin = gene expression activated
14
Q
What is heterochromatin?
A
- Inactive form of chromatin
- Gene expression inactivated
15
Q
Types of regulation of chromatin structure
A
1) Histone modification
2) DNA methylation
16
Q
Define nucleosome
A
- Basic structural unit of DNA
- Segment of DNA around see of 8 histones = octamer
17
Q
Describe histone acetylation
A
- Histone acetylation enzymes = promote initiation of transcription = remodel chromatin structure
- N terminal of histone = protudes from nucleosome
- Acetyl group attached to + charged lysines in histone tails
- Lysine acetylated = neutralized = histone tails don’t bind to neighbouring nucleosomes
- Chromatin = looser structure = activation of transcription
18
Q
Describe histone deacetylation
A
- By histone deacetylase
- Removes acetyl group = restore + charge = increases binding between neighbouring nucleosomes
- Inactive chromatin = inactivation of transcription
19
Q
Describe histone methylation
A
- Add methyl group to amino acid = lysine/arginine in histone
- Chromatin condenses
- Gene expression inactive
- Associated with transcriptional repression BUT some result in transcriptional activation
20
Q
Describe histone phosphorylation
A
- Add phosphate group to amino next to methylated amino
- Decondenses chromatin
- Activates transcription
21
Q
Describe DNA methylation
A
- Add methyl group to base = cytosine = reduced transcription
- Causes long-term inactivation of genes
- Heavily methylated cell not expressed
22
Q
Describe methylation of IGF2
A
- IGF2 growth factor = fetal development
- Inactive in humans = maternal allele silenced by methylation
- Abnormal activation of maternal IGF2 during egg formation = Beckwith Wiedemann syndrome
- Syndrome = increases risk of cancer
23
Q
What are the control elements?
A
- Non-coding DNA = regulates transcription by binding to transcription factors
- Proximal control elements = located close to promoter
- Distal = enhancer = away from gene or within intron
24
Q
Define transcription factors
A
- Proteins helping RNA polymerase initiate transcription
- Interact with control elements
- Control elements + transcription factors = regulation of gene expression in different cells
25
Types of transcription factors
SPECIFC
1) Activators = bind to enhancer = stimulate specific gene transcription
2) Repressor = inhibit transcription + expression of gene
GENERAL
- Common for all genes
- Bind to TATA box = induce RNA polymerase binding to promoter
26
Describe activators
- Unique for each gene
- Common for functionally related genes = need to be co-expressed
- Bound activator = recruit mediator proteins
- Recruit general TF = bind to TATA box
- Recruit RNA polymerase = binds to promoter
- Activation of gene transcription
27
Describe co-expression of genes in prokaryotes
- Functionally related genes of operons = regulated by same promoter
- Production of = polycistronic mRNA = encodes multiple polypeptides = co-expressed
28
Describe co-expression of genes in eukaryotes
- Each gene has own promoter
- Production of monocistronic mRNA = encodes for 1 polypeptide
- Functionally related genes = same control element + activators even if on different chromosomes
- Activators recognize control elements = promote simultaneous transcription of genes = co-expressed
29
Why are there different types of β-thalassaemia?
- Due to abnormal splicing of β-
globin gene
30
Define mRNA degradation
- Nucleases + non-coding RNA = induce degradation
- Inhibition of gene expression
31
What is the function of non-coding RNA?
- Regulate mRNA translation + chromatin configuration = regulate gene expression
- mRNA degradation
- Initiation of translation
32
Define non-coding DNA
- Transcribed but not translated
- Has gene for rRNA + tRNA
- Significant amount trnascribed into non-coding RNA
33
Define microRNA
- Small + single strand RNA = 20-25 bp = bind to mRNA = degrade mRNA + block translation
34
Define small interfering RNA
- Small + double stranded RNA = 20-25 bp = bind to mRNA
- Cause RNA interferance = inhibit gene expression of RNA molecule
35
Give DNA viruses associated with cancer
- Epstein-Barr virus
- HPV
- Hepatitis B
- Burkitt’s lymphoma
- Nasopharyngeal carcinoma
- Cervical carcinoma
- Heptocellular carcinoma
36
Give RNA retroviruses associated ith cancer
- HTLV-I
- Adult T-cell leukaemia
- Lymphoma
37
Define acutely transforming
- E.g. Avian Erythroblastosis virus
- Virus genome = oncogene
- By inserting into genome of cell = uncontrolled proliferation of cells = carcogenesis
38
Define non-defective
- E.g. mouse mammary tumor
- Virus genome NOT contain oncogene
- Strong viral promoter causes uncontrolled proliferation = carcinogenesis
39
Define oncogene
- Gene found in viral/cellular genome = triggers molecular event = lead to cancer
- Induce uncontrolled cell division
40
Define proto-oncogene
- Nornal cellular gene = responsible for normal cell growth + divison
- Mutation > oncogene
41
How are proto-oncogenes converted to oncogenes?
- Via amplification of proto-oncogene = increased number of gene copies
- Increased activation of MAPK signaling pathway
- Increased cellular proliferation
42
What is Trastuzumab/Herceptin?
- Monoclonal antibody targeting HER2
43
Explain the mechanism of inactivation of tumor suppressor genes
1) Loss of function mutation = mutation = inactivates gene = inactivates proteins = cancer development
2) Insertional mutagenesis = insertion of viral genome into host cell DNA = inactivates gene = inactivates protein = cancer
44
What is the role of a tumor suppressor protein?
- Inhibits cell signaling pathways = onhibits cell cycle + induces apoptosis
- Repairs damaged DNA
- Controls cell adhesion
45
Give inherited mutations
- In tumor suppressor gene = APC = colorectal cancer
- In BRCA1/2 = breas cancer
