Post -transcriptional Regulation Flashcards
1
Q
What’s the first major control point of gene expression.
A
Transcription at initiation, elongation, termination
2
Q
What is the 2nd control point of gene expression
A
Post transcription process at capping, polyadenylation and splicing.
3
Q
What is the 3rd control point for gene expression
A
Functional mRNA transported to cytosol
4
Q
What is the 4th control point of gene expression
A
Translation at initiation, elongation and termination.
5
Q
What is mRNA capping ?
A
It is the adding of a methylated guanine added to 5’ end, and this capping occurs simultaneously with transcription.
6
Q
Explain the unique covalent bond utilised in mRNA capping.
A
- Three phosphates separate the Me-G from the first mRNA residue.
- 5’-5’ bond is used (not a standard 3’-5’ phosphodiester bond) Example: 3’G5’PPP5’NNNNN3’
7
Q
Two enzymes required for capping
A
- Guanylate transferase: add G to 5’ end.
2. Guanine methyl-transferase: Add Me to N7 of G
8
Q
Define polycistronic
A
MRNA Containing the genetic information for the synthesis of more than one protein.
9
Q
Initiation of translation of prokaryotes mRNA.
A
- Ribosome initiate translation internally, guided by shine-dalgarno sequence.
10
Q
Initiation of translation of eukaryotic mRNA.
A
Translation initiated by 40s ribosomal subunit binding to Me-G cap.
11
Q
Are prokaryotic mRNA polycistronic or monocistronic
A
Typically polycistronic
12
Q
Are prokaryotic mRNA polycistronic or monocistronic
A
Typically monocistronic that lack guide sequences.
13
Q
What is the shine-dalgarno sequence.
A
The shine-Dalgarno sequence is a ribosomal binding site in prokaryotic messenger RNA, generally located around 8 bases upstream of the start codon AUG.
14
Q
What is the function of the shine-dalgarno sequence.
A
The RNA sequence helps recruit the ribosome to the messenger RNA (mRNA) to initiate protein synthesis by aligning the ribosome with the start codon.
15
Q
The Shine-Dalgarno sequence exists in?
A
Found in bacteria and archaea, It is also present in some chloroplast and mitochondrial transcripts.
16
Q
What is the six-base consensus sequence of the shine-dalgarno sequence.
A
AGGAGG
17
Q
What are the Kodak’s rules?
A
- In eukaryotes, translation is not initiated at the first AUG triplet.
- The AUG triplet must be set within a consensus sequence
- The scanning hypothesis state that the ribosome moves along the mRNA looking for the consensus sequence to initiate translation.
18
Q
Why aren’t rRNA recognised by the translational apparatus ?
A
Because the rRNA do not contain the 5’-Cap
19
Q
What is the function of 5’cap
A
The 5’ end of all mRNA are recognised by the translational apparatus to allow for the initiation of translation.
20
Q
In the cytosol the 5’-cap is recognised by:
A
- 40S ribosomal subunit
2. Translation initiation factor eIF4E that results in recruitment of additional translation initiators.
21
Q
How does Capping protects the mRNA.
A
Uncapped mRNA have a free 5’-phosphate group that can be used by exonuclease to degrade the mRNA
22
Q
What is the role of the cap-binding complex (CBC) in the initiation of translation.
A
MeG-cap is recognised by cap-binding complex and the CBC is replaced by eLF4E in the cytosol to allow initiation of translation.
23
Q
Me-G binds to between which two amino acids?
A
Two aromatic (hydrophobic) amino acids
24
Q
Capping regulates elongation of a RNA transcript.
A
- Following initiated of transcription, a few nucleotides of thee RNA is made and the pTEF-b kinase is recruited.
- The kinase phosphorylate RNA pol 2 causing the RNA polymerase to pause.
- During this pause, the cap is added
- The kinase then again phosphorylate RNA pol 2.
- Transcription elongation continues
25
Why is the RNA polymerase 2 is paused then capped.
This mechanism is a checkpoint to ensure that a full mRNA transcript is not made unless it is correctly capped.
26
The two steps of polyadenylation.
1. Cleavage of transcript
| 2. Addition of (A)-tail
27
Cleavage site flanked by:
1. Upstream AAUAAA
| 2. Downstream: G and U rich area.
28
The upstream AAUAAA is recognised by which protein ?
CPSF (cleavage and polyadenylation-specificity factor)
29
The downstream : G and U rich area
CstF (Cleavage stimulation factor)
30
Which enzyme adds The polyA -tail.
PolyA-polymerase Adds As
31
Steps of adding a poly A tail to mRNA.
1. The CPSF bind to the AAUAAAA sequence and the CstF proteins binds to the G/U sequence of the mRNA.
2. THE CPSF and CstF proteins bind to each other causing the mRNA to bend, at the bend of the mRNA endonucleolytic cleavage occurs.
3. This splits the mRNA into two pieces of mRNA, the piece of mRNA containing the AAUAAA has a poly-A-tail added to it by poly-A-polymeras.
4. The mRNA piece containing the G/U sequence is degraded.
32
Roles of the polly-A tail:
1. Protects mRNA from exonuclease degradation (increased stability)
2. Regulate efficiency of translation.
3. Function in regulation of controlled mRNA degradation
33
Polyadenylation is linked to:
1. Transcription via phosphorylation of RNA pol 2 serine 2
| 2. Translation
34
The splicesome
1. Specific structure within the nucleus
2. 5 RNA molecules: 56-271 bases, rich in uridine
3. Large and small subunit distinguishable.
35
Almost all eukaryotic intron transcribed by RNA pol 2 begin and end with what bases ?
Introns begin with GU and end with AG.
36
Initiation of splicing steps:
1. U1 snRNP bind to 5’-splice site .
2. U2 snRNP binds to branch point A in the polypyrimidine tract.
3. U5 snRNP binds to upstream exon
4. U6 replaces U1 in the complex
5. U6 and U2 interacts bringing splice site close to the branch A-residue.
37
What enzyme activity splice out intron.
Endonuclease activity
38
What enzyme mediates release of joined exons from spliceosome.
RNA helicase (Prp22)
39
How does the U-RNA recognise the mRNA molecule.
1. Normal complementary Watson-crick base pairing.
| 2. Example: U2 snRNP recognise branch point region of the mRNA.
40
Why does the upstream exon not float away after cleavage ?
Spliceosome component hSLu7 holds it in close proximity to the AG of the correct 3’-splice site.
41
Serine and arginine proteins (SR proteins)
1. Associated with spliceosome (but not with the snRNA)
2. Mediate the recruitment of snRNPs to the mRNA.
3. Determine which splice sites will be joined.
4. Bind to exon-splicing enhancer sequences ( ESEs) which ensures exon is included.
5. One way in which exon-skipping/ alternative splicing is mediated.
42
What happens if the are mutations in ESE.
Mutations in ESE prevent SR protein binding results in exon being spliced out. This is called exon skipping.
43
Alternative splicing
Different combinations of exons joined
44
Majority of splicing via what pathway.
GU-AG pathway , exclusively nuclear.
45
Minority via what way.
1. AU-AC pathway
2. This pathway utilise different snRNPs
3. Pathway may also occur in cytoplasm.
46
What snRNPs are used in the AU-AC splicing pathway.
U11, U12, U4atac, U5, U6atac
47
Phosphorylation of serine 5 of CTD.
1. Initiation of transcription
2. Recruitment of capping factors
3. Capping stimulates serine 2 phosphorylation
48
Phosphorylation of serine 2 of CTD
1. Stimulate transcriptional elongation
| 2. Recruit 3’ processing and polyadenylation factors.
49
Transcription initiation and elongation are coupled
1. CBC interact with the spliceosome, This links capping and splicing.
2. Spliceosome (U2 snRNAP) interact with the CPSF polyadenylation factor, this links splicing and polyadenylation.
50
Splicing can sometimes continue after capping and polyadenylation, what does this depend on ?
This depends on the rate of transcription.
51
Explain how the rate of transcription can cause splicing after capping and polyadenylation has taken place.
1. Tightly packed chromatin structure means elongation is slow, leaving enough time for splicing to take place before polyadenylation.
2. Open chromatin structure because of trimethylation means that elongation is enhanced, because of the enhanced elongation splicing may not have enough time for all introns to be removed thus splicing will continue after the RNA has been released.
52
Where does RNA transport occur ?
Transport occurs in nucleus regions located adjacent to nuclear pores.
53
RNA exporter complex ( REC)
1. Two proteins comprise the REC complex
| 2. REC recruited via protein protein interaction with existing mRNA bound proteins, such as SR-proteins
54
How does phosphorylation control REC-SR protein association.
1. Phosphorylate SR: involved in splicing, cannot recruit REC.
2. De phosphorylation of SR occurs after splicing, allow binding of REC.
55
What is the function of coupling of splicing and RNA transport.
Coupling of splicing and RNA transport ensure that no intron-containing mRNAs are transported to the cytoplasm for translation.
56
Steps of coupling of capping, transport and translation.
1. TREX proteins binds to CBC on 5’ end
2. This allows for recruitment of REC
3. 5’-end is the first pass into the cytoplasm
4. Allow for rapid initiation of translation.
57
The REC complex can bind to:
1. SR proteins (splicing )
2. TREX (capping)
3. Outer 5’-capping binding proteins
4. Numerous splicing factors
5. 3’ polyadenylation factors
58
How does ubiquitination regulate the interaction between REC complex and CPSF.
1. ubiquitination of histone 2B promotes the ubiquitination of CPSF.
2. This promotes binding of REC for rapid export of mRNA
3. Link between chromatin structure, post-transcriptional process and transport.
59
What is FACT ( facilitates chromatin transcription)
A heterodimeric protein complex that affects eukaryotic RNA polymerase 2 transcription elongation.
60
What is the function of FACT (facilitates chromatin transcription)
It is responsible for the remodelling of nucleosomes in front of RNA polymerase and the re-establishment of nucleosomes integrity.
61
Purifies do human FACT binds specifically to?
mononucleosomes and the histone H2A/H2B dimer, but not to the H3/H4 tetramer.
62
RNA degradation can occur where ?
Nucleus and cytoplasm
63
When does degradation occur in the nucleus.
Incorrectly post -transcriptional processed mRNA and introns are degraded in the nucleus.
64
When does degradation occur in the cytoplasm ?
Non-functional mRNA are degraded in the cytoplasm this is called nonsense -mediated RNA decay)
65
Degradation is carried out by which molecules and describe the molecule.
1. Degradation is carried out by Exosomes.
| 2. Exosomes are multi-protein complex’s with 3’-5’ exonuclease activity.
66
Steps of degradation
1. Deadenylation
2. 3’ to 5’ degradation via exonuclease
3. De-adenylation dependent decapping
4. 5’ to 3’ degradation via exonucleases.
67
Cytoplasmic degradation occurs in?
P-bodies
68
P-bodies are rich in?
Rich in decapping enzymes and Exosomes.
69
How are abnormal mRNAs recognised and directed to degradation pathway ?
1. Recognition of incorrect localisation of stop codon initiate degradation, this incorrect localisation should be located in the last exon, downstream of the exon junction complex (EJC)
2. EJC binds to each exon during splicing and remains associated during transport. It is replaced by ribosomes during translation .
70
Steps on how abnormal mRNAs recognised and directed to degradation pathways.
1. Incorrect stop codons cause premature translation termination.
2. The EJC remains attached.
3. This signals recruitment of the surveillance complex (SURF )
4. SURF recruits enzyme that degrade mRNA.
71
What activities have been demonstrated to occur in or to be, associated with P-bodies.
1. Decapping and degradation of unwanted mRNAs
2. Storing mRNA until needed for translation.
3. Aiding in translational repression by miRNAs (related to siRNAs)
72
The central dogma of biology
DNA is converted into RNA via transcription and RNA is converted into protein via translation.
73
The human genome contain how many genes
+/- 25 000
74
The human genome codes for how many proteins
+/- 400000
75
If genomic DNA is the same for all cells what causes diversity in cell expression .
Post-transcriptional regulation drive mRNA and protein diversity.
76
How do different cells have different proteomes ?
1. Cells make cell-specific transcription factors and splicing factors (ISS, ISE, ESS, ESE), this means different promoters on the gDNA template are recognised, therefore different mRNAs are transcribed. The mRNA are also spliced differently to produce different proteins.
2. Cells have different cell-specific regulatory functions
77
What are the RNA secondary structure
1. Helix
2. Stem loop
3. Pseudoknot
78
What are the RNA tertiary structures
1. Formed from helix secondary structure= A-form, B-form, z-form
2. Formed from stem loop secondary structure = stem loop
3. Formed from the Pseudoknot secondary structure= Pseudoknot
79
What happens to unsliced RNA ?
1. Unspliced RNA is degraded within the nucleus or
2. Transported to the cytoplasm where they are unable to make a functional protein so the are degraded via nonsense mediated degradation pathway.
80
Alternative splicing is a frequent process in which processes?
1. Embryonic development
2. Sex determination
3. Muscular contraction
4. Neuronal functioning
81
5 models of how alternative splicing is mediated.
1. Differential use of promoters
2. Folding of the transcript
3. Trans-acting proteins that bind to cis acting sites.
4. Rate of transcription elongation
5. Amount of splicing factors present
82
Model 1: differential use of promoters
1. Two alternative transcripts are produced by transcription from different promoter elements.
2. Results in Situations where the 5’- end of the alternatively processed transcript is different
3. Two promoters can occur upstream of the first exon or may be separated by exons yielding alternative spliced transcripts.
4. Different promoters sequence recruit different TFs, position RNA pol on different sites resulting in different lengths of mRNA are formed.
83
Model 2: folding of the pre-mRNA transcript
1. Different splicing protein complexes are recruited to different pre-mRNA depending on how they are folded.
2. The way pre-mRNA are folded depending on their sequence and rate of transcription.
84
Model 2: Cis-regulatory factors.
This is mediated by tissue specific splicing factors that binds to ESE, ESS, ISS,ISE sites.
85
Two types of splice sites caused by splice factors under model 3.
1. Promoting of splice sites: If splice factor is bound it will promote splicing of one exon to the exon next to it.
2. Inhibiting of a splice site: if splice factor is bound it will inhibit splicing of the one eon to the exon next to it.
86
Explain the mechanism of alternatively spliced mRA is regulated by a system of trans-acting proteins (opposite functions) that bind to cis-acting sites (same function) on the primary transcript itself.
This is when splicing activators that promote the usage of a particular splice site, and splicing repressors that reduce the usage of a particular site work together
87
What are SREs present in exons.
1. Exotic splicing enhancers (ESEs)
| 2. Exotic splicing silencers (ESSs)
88
SREs present in introns
1. Intrinsic splicing enhancers (ISE)
| 2. Intrinsic splicing silencer (ISSs)
89
Model 4: rate of transcription elongation influence alternative splicing.
If an upstream splice site is weaker than a downstream one:
1. a low rate of elongation will enhance the changes of utilising the weak site.
2. A fast rate of elongation will yield both sites of splicing and the stronger site will be favoured.
90
What type of binding does slow transcription allow
Binding of proteins with both high and low affinity ca occur
91
What type of binding does rapid transcription allow
Binding of proteins with high affinity will bind preferentially .
92
Model 5: concentration of splicing factors present.
SF2 (a type of SR protein)
1. High [SF2]- favour proximal splice site (sufficient SF to bind to every splice site)
2. Low [SF2] favour distal splice site. ( sufficient SF at start of process, but then insufficient to bind to every other splice site)
93
Genome- wide analyses of alternative splicing
1. Microarrays
| 2. Proteomics
94
How Microarrays is used in genome-wide analyses of alternative splicing
Microarrays containing oligonucleotides from various exons can be hybridised with mRNAs from different tissues to identify alternative splicing events.
95
How proteomics are used in genome- wide analyses of alternative splicing.
1. Proteomics allows the analysis of proteins produced by specific tissues under a specific set of conditions.
2. Proteins mixture separated via 2D-electrophoresis
3. Protein spots analysed via peptide-mass finger printing using mass spectroscopy
4. Amino acid sequence information allows for the identification of distinct but related proteins formed via alternative splicing.
96
What exons are used in mature mRNA depends on:
What exons are used depends on:
1. How fast transcription happens
2. What structures form ( different structures are recognised by different proteins)
3. What proteins bind
97
Deamination by cytidine deaminase causes?
Cytosine to be converted into uracil.
98
Example of RNA editing :C to U changes
1. Apolipoprotein
2. Only one coding mRNA in both tissue so it is not a splicing effect.
3. In the liver a large protein is produced from the mRNA.
4. In the intestine a small protein is produced from the same mRNA, this is because of a C to U edit causing a stop codon in the mRNA sequence where there originally was no stop codon.
99
Deamination by adenosine deaminase causes?
Adenine to inosine change
100
What is useful about the incorporation of inosine into the mRNA.
Inosine can bind too C, U or A
101
Inosine is read as what nucleotide during the translation process.
Guanosine
102
A to I change cause
1. A change in the amino acid sequence of the encoded protein, or
2. It changes the alternative slicing sites.
3. Change in mRNAs targeted by miRNA.
103
Example of RNA editing used in the body.
1. In the neuronal system, receptors can change their sensitivity towards calcium by a sing amino acid change.
2. In the glutamate receptor, an A to I change cause Gln to Arg change.
104
Codon CAU codes for amino acid His. What amino acid does it code for after RNA editing.
RNA editing produces: CIA
| Read as: CGA which codes for amino acid Arg
105
How does A to I change can influence splicing of the editing RNA .
1. If adenosine deaminase causes an AG in a sequence in an intron where one should not be, this can be read as an AG 3’ -splice site.
2. This causes incorrect splicing of the mRNA resulting in a premature stop codon in the mRNA sequence and mRNA will be degraded
106
RNA editing A to I of miRNA allows for?
Creates One miRNA that can bind to multiple mRNA because inosine can bind to C, U and A.
107
Regulation of RNA transport
1. RNA transport proteins contain a nuclear export signal (NES)
2. NES region of RNA transport proteins bind to export proteins that occur in the pores of the nucleus membrane.
3. RNA transport pathway can be constitutive or regulated by specific stimuli in specific cells/ tissues.
4. MRNA is exported as a complex particle of mRNA and numerous proteins .
108
Regulation of RNA stability
1. Turnover of mRNA determine the amount of protein produced.
2. Regulatory signals can influence mRNA stability
109
How do hormones mediate RNA stability.
Via regulation of the expression of various mRNA binding proteins that block or recruit various endo and exonucleases.
110
What is the Specific sequence in the mRNA THAT REGULATES its stability.
3’-untranslated regions form stem-loop structures, enhancing mRNA stability.
111
Polyadenylation impacts gene expression via regulating:
1. Stability of mRNA
2. Transport of mRNA into cytoplasm
3. Translation
112
What is the effect of interrupting polyadenylation.
A polyA tail is not added to the 3’ end of the mRNA, this results in the mRNA not being able to be transported out of the nucleus into the cytoplasm for translation.
113
What enzyme adds the poly-A-tail to the mRNA.
Poly(A) polymerase (PAP) which is associated with poly((ADP-ribose) polymerase (PARP1)
114
What happens when the cell is going under stress.
1. Stress of the cell causes activation of PARP,
2. which leads to modification of PAP by addition of poly(ADP-ribose) molecules to PAP.
3. This leads to the inhibition of polyadenylation.
115
Examples of RBPs involved in RNA maturation.
1. CSTF
2. CstF
3. Poly (A) polymerase (PAP)
4. Poly(DAP-ribose) polymerase (PARP)
116
The function of Poly(ADP-ribose) polymerase (PARP)
An enzyme that add single residue of ADP-ribose OR long polymers of ADP-ribose to target proteins. This process is called PARylation.
117
What does the addition of ADP-ribose molecules do to the target protein.
They change the target proteins function.
118
What enzyme is responsible for removing ADP-ribose
Hydrolase
119
What process involving DNA does PARP affect
1. Chromatin remodelling
2. DNA repair
3. Transcriptional regulation
120
What process involving mRNA does PARP affect
1. MRNA synthesis
2. RNA export
3. MRNA stability
121
Role of miRNA of in mRNA stability.
MiRNA bind to target mRNA which induce de-adenylation of previously polyadenylated mRNA . Which influences mRNA stability and enhance degradation
122
3 different models of regulation of polyadenylation.
Model 1: PARP
Model 2: miRNA
Model3: Ig
123
How does polyadenylation sites affect immunoglobulins
Polyadenylation occurs different positions causes transcripts that are then differential LH spliced.
124
Examples of how immunoglobulins are affected by polyadenylation sites.
1. First polyA site (higher up on the mRNA) creates a short isoform that becomes secreted Ig
2. Second polyA site (lower up on the mRNA) creates a longer inform that becomes membrane bound Ig.
125
How do B-cells switch between the two polyadenylation signals ?
1. Dependent on the concentration of CstF
2. The sequence surrounding the polyadenylation sites creates a strong and weak binding sites for CstF.
3. At low concentration of CstF, it will favour and bind to the strong affinity site
4. At high concentration of CstF, there’s more than enough to go amours so it will bind to the weak affinity site. Thus cleavage will occur at the first polyA site, resulting in a shorter immunoglobulin.
126
Function of ELF4E
ELF4E binds to the cap structure of the mRNA this is followed by the binding of Elf4A and ElF4G to ELF4E forming the ELF4F complex.
127
Function of ELF2
Binds to tRNA and small subunit and brings them to the mRNA.
128
How is translation regulated by Elf2A during starvation
Translation is repressed via phosphorylation of ELF2A.
129
How does the phosphorylation of elfba repress translation during starvation.
1. The phosphorylation of elF2A
2. Causes the formation of Stable P-eLF(GDP)-elF2B complex. Which is ( elf2A-GDP+ elf2b)
3. The formation of this complex means that the eLF2A can no longer bind to the GTP
4. IF eLF2A isn’t bound to GTP it will not bind to tRNA(met), small ribosome and mRNA meaning initiation of translation will not occur.
130
How can some specific proteins be translated in response to a stress signal, when the elf2/elF2B pathway is inhibited during starvation.
One example is expression of.amino acid transporters during starvation.
To translate these amino acid transporters the ribosome will initiate translation from a internal ribosome entry site(IRES)
131
Mechanism of IRES-induced translation.
1. Translation of upstream open reading frame will change the structure of the mRNA exposing the IRES (internal ribosome entry site).
2. This allows phosphorylated elF2 to bind to the IRES and initiate the translation of an amino acid transporter protein.
132
Function of eLF4G
Drives cap depndent translation.
133
If cancer cells are stimulated to undergo apoptosis.
1. ELF4G i degraded by proteases
2. This halt cap-dependent translation
3. mRNA coding for apoptosis proteins contain IRES sites which allows for translation via cap-independent mechanism.
134
What drives IRES (internal ribosome entry site)
1. Phosphorylation of eLF2
| 2. Lack of eLF4G
135
How translation still occurs even if elf2 is phosphorylated.
1. The use of IRES
| 2. The use of different start codons
136
Steps on how translation is still continues in starvation after normal translation is halted by using regulation via use of different initiation codons.
1. The concentration of t-RNA NOT bound to amino acids increases, and this activates a kinase which phosphorylates eLF2.
2. Phosphorylated elf2 causes ribosome not to reinstate translation at three of the upstream sites.
3. Rather it increase translation from the downstream site allowing for translation of full length GCN4
137
What is an example of regulation via use of different initiation codons during starvation.
1. The GCN4 transcriptional regulatory protein is regulated by small peptide-encoding region in 5’ UTR.
138
What happens to the translation of the GCN4 proteins when the cell is under normal conditions (not starving) and normal translation can take place.
When normal translation is taking place the translation of peptides 2-3 amino acids in lengths causes the ribosomes to fail to produce full-length GCN4 proteins .
139
How does insulin afferent translational regulation .
1. When insulin or growth hormone stimulates a cell.
2. Insulin will phosphorylate the elF4Ebp bound to the eLF4E inhibiting Translation, allowing the eLF4Ebp to release from the eLF4E.
3. Once the eLF4E is free it can recruit eLF4A and eLF4G allowing for their helicase activity to unwind the DNA, initiating translation.
140
How iron effects ferritin production?
Increases ferritin production by binding to the IRE BP bound to the 5’ untranslated region, releasing the IRE BP. Allowing the ribosome to reach the start codon and for translation to occur.
141
How iron effects transferrin receptor production
Decrease in transferrin receptor by binding to the IRE BP bound to the 3’ stem loop, decreasing mRNA stability, causing rapid degradation of the transferrin mRNA.
142
What happens to transferrin receptor translation when there is no iron present.
The IRE BP protein binds to the 3’ loop on the mRNA allowing translation and the production of the receptor for iron.
143
What happens to ferritin receptor translation when there is no iron present.
The IRE BP binds to the 5’ stem loop blocking the ribosome from reaching the start codon, thus inhibiting translation.
144
Function of miRNA
Control of cellular gene expression
145
Function of siRNA
Control of viral and cellular gene expression
146
Are miRNA single-or double stranded RNA
Single stranded
147
Are siRNA single-or double stranded RNA
Double
148
Difference between complementary of miRNA and siRNA
SiRNA: Always fully complementary to mRNA
MiRNA: partially or full complementary, typically target the 3’ untranslated region of the mRNA.
149
Difference between siRNA and miRNA mRNA target.
SiRNA: only one target
MiRNA: multiple (could be over 100 at the same time)
150
Difference between siRNA and miRNA mechanism of gene regulation.
SiRNA: Endonucleolytic cleavage of mRNA
MiRNA: translation repression, degradation of mRNA, endonucleolytic cleavage of mRNA.
151
Difference between miRNA perfect complementary and partial complementary.
1. Perfect complementary: results in Endonuclease cut, that would lead to mRNA degradation.
2. Partial complementary: inhibition of translation (mRNA not degraded.) or deadenylation and exonuclease digestion (mRNA degraded).
152
Small RNA signal for what protein to cause degradation.
The RISC protein (RNA -inducing silencing complex)
153
What happens if there is a perfect match that occurs between a small RNA and target.
The target is cleaved
154
What happens in the absence of a perfect match between miRNA and DNA.
Argonaute does not cleave target, but induces polyadenylation and subsequent degradation.
155
Binding of small RNA to its target mRNA can block translation by in what ways?
1. Blockage of translation initiation
2. Blockage of translational elongation
3. Blockage of translation re-initiation
156
How does miRNA repress translation initiation.
1. MiRNA can inhibit translation initiation via the 5’ CAP.
2. Some argonaute proteins resemble eLF4E and so argonaute and miRNA can be recruited to the cap, blocking binding of ELF4E and 40s.
157
How can miRNA can repress translation elongation.
1. MiRNA-RISC complex can associate with elf6 (prevents premature association of 40s and 60s), blocking 60s binding. (Strong repression can use both eLF4E and eLf6 pathway.)
2. Physical blockage of initiation
3. Inducing degradation of the nascent protein via a protease (breaks down protein) associated with the RNA-induced RISC complex.
158
How can miRNA block translation re-initiation.
1. MiRNA and RISC can block the eLF4G-PABP ( mediates circular formation) interaction resulting in loss of re-initiation of translation.
159
Why do mRNA and DNA have folded structures?
These structures are there so that proteins can recognise these structures and bind.
