Heinemann Final Flashcards
(147 cards)
1
Q
What are 2 “extra” amino acids?
A
selenocysteine and pyrolysine
2
Q
What are ribozymes?
A
segments of RNA that display enzyme activity in the absence of protein
3
Q
What are abzymes?
A
antibodies raised to bind the transition state of a reaction of interest
4
Q
What part of the ribosome has the catalytic activity?
A
the RNA
5
Q
Describe the composition of the ribosome according to molecular weight
A
2/3 RNA
1/3 protein
6
Q
Do rRNAs contain modified nucleotides?
A
yes
ie pseudouridine and ribothymidylic acid
7
Q
What are the subunits of the prokaryotic ribosome?
A
30S and 50S
overall is 70S
8
Q
What are the subunits of the eukaryotic ribosome?
A
40S and 60S
overall is 80S
9
Q
What is streptomycin?
A
an aminoglycoside antibiotic
it induces mRNA misreading by binding to the small 16S rRNA of the 30S subunit of the bacterial ribosome
slows rate of bacterial growth
does NOT bind the eukaryotic ribosome
10
Q
What is puromycin?
A
binds at the A site of BOTH prokaryotic and eukaryotic ribosomes and accepts the peptide chain from the P site
this terminates protein synthesis
11
Q
What is found on the 3’ end of tRNA?
A
CCA
this is where the amino acid gets ligated to the tRNA
12
Q
How long are tRNAs? Are there any modified residues?
A
73 to 94 residues each
many bases are methylated
about a 1/3 of the bases are post-transcriptionally modified
13
Q
How is charging a tRNA with the right amino acid usually done?
A
by excluding other amino acids from the active site
14
Q
What is one tRNA that often gets charged with the wrong amino acid?
A
proline’s tRNA sometimes gets Cys put on it
ie 1 in 100 are wrong
15
Q
What is RNase P?
A
ribozyme
cleaves the 5’ end of tRNAs because they are longer than they need to be when they are made
(exonuclease does the 3’ end)
16
Q
What is the hammerhead ribozyme?
A
an RNA sequence that promotes its own cleavage
we use them in the lab when we make tRNA because we don’t have RNaseP to cleave them
17
Q
Describe Sol Spiegelman’s monster experimen
A
used RNA from a bacteriophage
its RNA replication enzyme
some free nuts and salts
the RNA started to replicate
after 74 generations the 4500 nt ended up being 218 nt (didn’t shorten again after this)
this showed that RNA could be replicated without DNA, but this still needed protein
18
Q
Have any self replicating RNAs actually been discovered?
A
yes but only up to 14 nuts have been done and this is under lab conditions, high [ ]s etc
19
Q
What is needed for RNA-catalyzed RNA replication?
A
ribozyme
RNA template strand
RNA primer
20
Q
What is the RNA world hypothesis?
A
early life forms lacked protein enzymes and depended instead on enzymes composed of RNA
21
Q
What are DNA ptotoviruses?
A
DNA genes
RNA enzymes
22
Q
What is the origin of the nucleotides in an RNA world?
A
aminoimidazolecarbonitrile
turns into adenine
glycolaldehyde to ribose
both adenine and glycoaldehyde exist in outer space
23
Q
What are 3 things that support the RNA world hypothesis?
A
RNA’s ability to store, transmit and duplicate genetic info
RNAs can act as enzymes
RNA genomes in viruses
24
Q
Why does the RNA world hypothesis say that life evolved to use DNA and proteins?
A
because RNA is unstable and has poorer catalytic properties
25
What are some things against the RNA world hypothesis?
many of the steps needed for the nts formation do not proceed efficiently in prebiotic conditions
large RNA molecules are inherently fragile
26
What are snRNAs?
components of the splicesosome
27
What are snoRNAs?
methylation of rRNAs
28
What percentage of genes are undergoing transcription in a typical cell at and given moment?
3%
29
How many RNAPs do bacteria have?
one
30
In what direction does transcription occur?
polymerase moves 3' to 5' and synthesizes 5' to 3'
31
What is the template strand?
the strand that base pairs with the new RNA i.e. the one that is being read by RNAP
32
What are the 4 stages of transcription?
binding of RNAP
initiation
elongation
termination
33
Explain binding of RNAP in bacterial transcription
subunit composition is alpha2betabeta'sigma (holoenzyme)
enzyme binds and scans along until sigma recognizes a promoter at the transcription start site which goes from -70 to +20
34
What is the closed promoter complex? Open promoter complex? What are the relative affinities of the enzyme for DNA?
closed = DNA is not unwound
open = DNA is unwound (12bp)
once the complex is opened the affinity is much higher
35
Describe bacterial promoters
~40bp on the 5' side of the transcription start site
there are 2 consensus elements
Pribnow box near -10 with consensus TATAAT
-35 with consensus TTGACA (this is where sigma binds)
36
What determines how sigma binds to the -35 region?
the more the sequence corresponds to the consensus sequence the greater the efficiency of transcription
37
What is bound in the active site of all polymerases?
Mg2+
38
What charge does the DNA-binding cleft of RNAP have?
positive
39
What are sigma factors?
proteins that bind in the major grooves of DNA using H-bonds
there is usually one household one that does most genes and then specialized ones for different stresses i.e. heat shock
(each one recognizes a different sequence)
40
What part of the DNA does sigma interact with in bacteria?
-35 and -10 regions of bacterial promoters
41
Describe bacterial transcription initiation
ATP/GTP are preferred as the first nucleotide (this is the initiation site)
RNA synthesis starts
after 6-10 nt sigma dissociates
42
What is the elongation site?
the 2nd NTP
43
What is a nucleoside?
no phosphate
44
Describe bacterial transcription elongation
core polymerase (i.e. without sigma) is the elongation enzyme
it moves ~20-50 bases/sec (slower in GC-rich regions)
is very accurate
while it is occurring gyrase introduces negative supercoils infront and topoisomerase removes then behind
45
What is DNA footprinting?
a way to find DNA that is covered with proteins
take DNA and protein mixture and just DNA mixture
digest with DNase
run on a gel to find where the protein was binding
46
Describe chain Rho-dependent termination in bacterial transcription
"tethered tracking"
Rho moves along with RNAP but is slower so it trails behind unless RNAP stalls
Rho recognizes rut, closes around RNA and advances toward RNAP
when RNAP slows down in a
GC-rich region Rho catches up and causes RNAP to dissociate because it induces a change in conformation in it
47
Describe intrinsic termination of bacterial transcription
there are inverted repeats at termination sites that are rich in GC and forma stable stem-loop structure in the transcript
the GC-rich area slows down RNAP
then there is a run of 6-8 As, and the Us in the transcript destabilize RNAP and it dissociates
48
What is "I" in an operon?
the regulatory gene i.e. the one that turns the operon on and off
isn't actually part of the operon, doesn't need to be close to the operon but it can be
49
Where is the operator of an operon located?
can be upstream or downstream
| usually close to the promoter sequence, but doesn't need to be
50
What are the genes in the lac operon used for?
LacY is a permease, brings lactose into the cell
LacZ is a galactosidase, it isomerizes lactose to allolactose
LacA transfers an acetyl group from acetyl-CoA to beta-galactoside
51
What are the 2 major regulators of the lac operon?
lactose- induction
| glucose- repression
52
How many promoters are there in the lac operon?
2
| one for the structural genes and one for lacI
53
Describe the lacI promoter
not regulated
promoter is very weak
LacI is a tetramer, only ~10 tetramers per cell, but this is enough
54
Where does LacI bind?
it has 3 operator sequences
there is one strong one upstream of lacZ
and 2 weaker ones on either side of it
these operators are palindromic
55
Explain how LacI regulates the lac operon
when lactose isn't present LacI binds to the operator and represses transcription
when lactose is present it gets converted to allolactose
allolactose binds to LacI and it can no longer bind to DNA
this allows transcription of the operon
56
Describe LacI and its domains
has a helix-turn-helix motif that binds to the major groove of the operator sequence
has allosteric site that binds the inducer
has an oligomerization domain because it functions as a tetramer
when allolactose binds there is a change in conformation and the H-T-H domains can't interact with DNA anymore
(inducer decreases the affinity of the repressor for DNA)
57
Is the lac repressor a positive or negative regulator of the lac operon?
negative
58
What is negative control? What is positive control?
```
negative = on unless turned off
postive = off unless turned on
```
59
What is CAP/CRP?
catabolite activator protein
dimer
N-terminus binds cAMP, C-terminus binds DNA
interacts with 27 to 30 bp of DNA
increases the affinity of RNAP to the lac promoter because it is weak
60
How does CAP work to increase transcription?
it binds upstream to the promoter to CAP sites
it interacts with RNAP through the alpha subunit and helps it bind tightly and recognize the promoter sequence
(assists in formation of the closed promoter complex)
61
When is cAMP low? When is it high?
cAMP is low when glucose is high
and high when glucose is low
i.e. when there is no glucose want it to bind to and activate CAP
(glucose entering the cell inhibits adenylate cyclase)
62
What are the binding sites for CAP?
TGTGA and TCANA
63
Can the lac operon be transcribed when glucose and lactose are both present?
yes because the repressor isn't there, but there will be very low levels of protein produced because CAP can't bind
64
How is the lac operon often used in the lab?
put the lac promoter in front of a gene that you want to express
add IPTG, a lactose analog when you want to induce transcription of your gene when the cells have grown enough to be ready to produce lots of protein
65
What are the structural genes in the trp operon used for?
proteins true through trpA (five of them)
| that are used in the synthesis of L-Trp
66
How does the Trp repressor work?
under negative regulation
when trp levels are high trp binds to TrypR which allows it to bind to the operator and reduce the rate of transcription 70-fold
67
What is trpL?
encodes the leader peptide
68
What operon is TrpR from? How is it regulated?
TrpR comes from the torpor operon
it regulates its own operon
this is called autogenous regulation
69
What is transcription attenuation? Can eukaryotes do it?
posttranscriptional gene repression
| only bacteria can do it because transcription and translation are coupled in them
70
What is the leader peptide of the trp operon?
139 nt segment of the operon that is transcribed under high W levels
71
Which segments of the trp operon transcription can base pair?
1: 2
2: 3 - anti-terminator
3: 4 - terminator
72
Explain attenuation in the trp operon
there are 2 UGG (W) codons together
when W levels are high the ribosome does not stall at them so the ribosome covers sequence 2 before 3 is transcribed
sequences 3 and 4 then base pair and form the terminator
when W levels are low the ribosome stalls at WW and RNAP keeps transcribing so the 2:3 anti-terminator sequence can form
the 2:3 structure is favourable to the 3:4 structure so if it can form it will
this can repress transcription 10-fold
(giving a total of 700-fold)
73
What is a solenoid?
6 nucleosomes per turn
74
What proteins make up nucleosomes? What influences the structure of nucleosomes?
4 different histones, 2 of each
| modifications on histone tails, also nucleosomes can influence each other
75
How do chromatin-remodelling complexes work?
they require ATP hydrolysis
| they move nucleosomes so that DNA is accessible to RNAP
76
Explain the covalent modification of histones
acetylated by histones acetyltransferases, this removes the positive charge from the histone so it has a lower affinity for DNA
phosphorylation of Ser, Tyr and Thr
methylation of Lys
both reduce the affinity
ubiquitination and sumolyation
reduce the affinity bc they're in the way and bc there are residues that can repel them
there are also accessory proteins that can make the DNA bind more
77
What is needed to start eukaryotic transcription?
transcription activators recruit chromatin-remodeling complexes and histone-modifying enzymes
then the DNA is accessible to transcription factors etc
78
How many types of eukaryotic promoters are there? How are they different from prokaryotic promoters?
3 because there are 3 polymerases
| they use transcription factors, enhancers, repressors etc which can be far away
79
What do the eukaryotic RNAPs transcribe?
```
I = pre-rRNA
II = mRNA (most snRNA and miRNA)
III = tRNA (some rRNA and others)
IV = siRNA in plants
V = RNAs involved in siRNA-directed heterochromatin formation in plants
```
80
What is amanitin?
poison from a mushroom that inhibits RNAP II
81
Describe the general structure of polymerases
palm has the catalytic activity
| fingers and thumb clasp the DNA
82
Explain the subunit of RNAP II
```
(all start with RPB)
1 = YSPTSPS C-terminal domain (like beta')
2 = NTP binding (like beta)
3 = core assembly (like alpha)
4 = promoter recognition (like sigma)
5-12 are all essential except for 9
```
83
Describe the C-terminal domain of RNAP II
projects away, isn't part of the core enzyme
has multiple YSPTSPS repeats, 5 of which can be phosphorylated
low phosphorylation is used for initiation
high phosphorylation is needed for elongation
this could be how it knows to start elongating
84
What is the TATA box?
TATAAA
eukaryotic promoter that is very well conserved
it is where general transcription factors bind
TATA binding protein (TBP) binds here
85
What are enhancers?
upstream activation sequences
they can be far away from the promoter
DNA loops and this allows multiple proteins to bind DNA sequences
86
What are response elements?
they are promoter modules in genes that are responsive to common regulation
ie HSEs
they are found in promoter regions
87
What elements are often involved in constitutive expression of eukaryotic genes?
TATA and GC boxes
| BLEs (basal level expression)
88
What is in the eukaryotic transcription initiation complex?
RNAP II
5 general transcription factors (GTFs)
a 20-subunit complex called Mediator (Srb/Med)
if there aren't TFs there is no binding of RNAP (like sigma in bacteria)
89
What do transcription factors do?
they bind to promoter elements and recruit RNAP II
90
Describe formation of the pre-initiation complex in eukaryotic transcription
TFIID which contains TBP binds to DNA
TFIIA stabilizes it and TFIIB orients TBP
TFIIF recruits RNAP II
TFIIE recruits TFIIH (helicase)
91
What is the minimal pre-initiation complex?
TBP, TFIIB, TFIIE, TFIIF and TFIIH
92
What does TBP do?
other GTFs will not bind unless it does
| it kinks and partially unwinds DNA
93
What does Mediator do?
required for transcription activation
it is a bridge between gene-specific activators bound to enhancers and RNAP II/GTF machinery at the promoter
transcription co-activators bind to enhancers and recruit it, bind to its tail, it then promotes the binding of GTFs and RNAP II at its head
can also act as a repressor and cause the GTFs and RNAP II to dissociate
94
Explain elongation in eukaryotic transcription
RNAP II pauses shortly after transcription initiation to wait for DSIF and NELF
about 25-60 nts in, basically waiting for a signal to keep going
the pause release is triggered by P-TEFb which phosphorylates CTD of RNAP II
phosphorylation causes NELF to dissociate and DSIF to turn into a positive elongation factor
then elongation can continue
95
What is abortive initiation?
dissociation of the transcription complex energetically competes with the elongation process
can return to open promoter complex
96
How is eukaryotic transcription termination thought to happen?
no termination sequences have been identified
| there are 2 models, torpedo and allosteric
97
Explain the torpedo model of eukaryotic transcription termination
mRNA gets cleaved after polyA signal sequence
RNase digests the remaining RNA
this disrupts the complex and RNAP dissociates
98
Explain the allosteric model of eukaryotic transcription termination
RNAP II becomes less protective after the poly-A signal sequence
99
How do activators work to activate eukaryotic gene transcription?
multiple activators may be required to switch a gene on
they can function synergistically
they bind to the enhancer and mediator
100
What are the 3 ways activators can function synergistically?
1. direct interaction i.e. they touch
2. interaction by a bridged protein that does not contact DNA
3. through recruitment of a chromatin modifier i.e. ones binds a modifier which modifies chromatin and allows another activator to bind
or binding of one can disrupt the nucleosome that is blocking the binding of the another
101
Why use synergy for gene expression?
allows for the integration of signals from more than one pathway at once i.e. different stressors at the same time
102
What is combinatorial gene expression? What organisms have it?
refers to one gene having multiple activators
| happens in both eukaryotes and bacteria, is extensive in eukaryotes
103
How does transcription repression work in eukaryotes?
does NOT block the promoter like in bacteria
repressors can either affect the activity of an activator i.e. block it from binding or it can affect RNAP directly or indirectly through other factors
ie repressors bind to enhancer or repressor sequences but not the promoter
could cause a conformational change in RNAP II, bind to nucleosome and recruit histone deacetylase etc
104
Explain how repressors can inhibit the activity of activators
either competitive i.e. compete for binding sites which are overlapping
or inhibition by binding to the activation domain of the activator (i.e. inactivate it instead of stopping it from binding to DNA)
105
How are the GAL genes regulated in yeast?
the genes all contain an upstream activating sequence (UAS) that is 17bp
it is a binding site for a transactivator called Gal4p
ie UASgal is an enhancer
106
What is Gal4p?
a transactivator
postive regulatory protein for Gal gene expression
homodimer
resemebles a Zn finger, but instead of 2 Cys and 2 His it has 6 Cys coordinating a Zn
has a DNA binding domain (N) and an activation domain (C)
107
How does Gal4p regulation work?
when there is NO galactose:
Gal4p binds to UAS
Gal80p binds Gal4p
functions as a co-repressor and covers the activation domain of Gal4p
when there IS galactose:
Gal3p binds galactose and enters the nucleus
Gal3p binds Gal80p causing it to bind below Gal4p
Gal4- can then activate transcription because its activation domain is free
108
How are bacterial inducers different from the way Gal4p activates transcription?
bacterial inducers have ligand binding and DNA binding on the same protein
in this case the inducer is being sensed by a different protein (Gal3p)
109
How can the GAL genes be repressed?
when glucose is present don't need them
Mig1 is a repressor that binds between UAS and GAL1
it recruits a repressor complex Tup1
Tup1 may recruit histone deacetylases and/or interact directly with transcriptional machinery
Note: this repression overrides induction!
110
Where does gene silencing occur? What is it?
on CpG islands which are commonly in 5' promoter regions
methylation of the Cs prevents transcription
methyl binding domain (MBD) proteins recognize Me-C in CpGs
111
Name 4 things that DNA methylation is essential for
genomic imprinting
X-chromosome inactivation
suppression of repetitive elements
carcinogenesis
112
What is anhydrotic dysplasia?
a disease that results in the absence of sweat glands
| the X-linked variant can result in mosaicism in females
113
How does genomic imprinting work?
epigenetic marks are removed in the fertilized egg
| waves of de- and re-methylation occur as normal reprogramming of cells
114
Explain non-specific protein-DNA interactions (in-direct readout)
base-independent
| interact with the backbone, phosphates, aromatic base stacking
115
Explain specific protein-DNA interactions (direct readout)
glutamine can recognize A, makes 2 H bonds with the A
| arginine can recognize G and make 2 H bonds with it
116
How do most proteins recognize and bind to their specific DNA sequence?
usually a combination of non-specific and specific interaction
ie non-specific helps make binding tighter and then specific can recognize consensus sequence
there can also be H bonding and salt bridges
proteins also have a 3D shape that is complementary to the DNA
117
What is KD equal to?
KD= Kd/Ka
118
How does EMSA work?
measure the strength of protein-DNA interactions
DNA is labelend with P32
DNA that is bound to protein won't move as far on the gel
keep increasing [protein]
plot [protein] vs fraction bound
can find the KD
119
What are the 3 most common DNA-binding protein motifs?
helix-turn-helix
Zn finger
leucine zipper basic region
120
Describe the helix-turn-helix motif
alpha helices fit into the major groove of B-DNA
AA side chains can read the bases
alpha helix diameter is 1.2nm, major groove is 1.2nm wide and 0.6-0.8nm deep
there are 3 alpha helices in the structure but only 2 are relevant to reading the DNA
3 fits in the groove, 2 stabilizes it, 1 binds other domains etc
121
What is an example of a helix-turn-helix motif?
homeobox domain proteins
lac and trp repressors
C-term of CAP
122
Describe Zn-finger motifs
either C2H2 or Cx
Cys and His are coordinated to Zn
C2H2 have Cys-X2-Cys-X12-His-X3-His domains that are separated by at least 7 or 8 (up to 12) AAs
Zn finger interacts with the major groove of DNA, can read about ants
can be repeated 13 times to read many bases
123
Describe bZIP
basic region leucine zipper
28-residue sequence with every 7th position a Leu and a basic region
every other "step" has a Leu so they stack
there are 3.6 residues per turn in an alpha-helix
leucine zippers dimerize, can be hetero or homo
Note: the leucine zipper doesn't recognize the DNA sequence, they are the dimerizaion domain
the basic region it what contacts the DNA
Myc, Fos and Jun are examples
124
How is 5' capping of eukaryotic mRNA done?
capping enzyme is bound to RNAP II
reaction is catalyzed by a guanylyl transferase
cap is added when the RNA is about 25-30nt long i.e. during transcription
5'-5' triester linkage
gets methylated at position 7 after it is added
additional methylations occur at 2'OH of the next 2 residues and 6-amino of the first A
125
What are the functions of the 5' cap on mRNA?
protection from degradation
enhancement of translatability
transport out of the nucleus
proper splicing
126
Where do the phosphates in the 5'-5' linkage of the cap in eukaryotic mRNA come from?
2 are from the transcript, 1 is from the GTP
127
What is Cap O? Cap 1? Cap 2? Which is most common
Cap O = only guanyl methylated
Cap 1 = methyl also on 2'OH of first nt
Cap 2 = methyl on 2nd nt
Cap O is always present, Cap 1 usually is
(Cap 1 is the most common)
128
What molecule methylates 5' caps?
S-adenosyl-L-methionine:mRNA (guanine-N7-)-methyltransferase
methyl group comes from SAM
129
What are the functions of 3' adenylation?
aids in transcription termination directs export of the mRNA and translation
protects 3' end from degradation
helps determine half life (when tail gets short enough the mRNA is degraded)
130
What is the polyA addition site? What is the other signal?
AAUAAA
| GU-rich region downstream of the polyA signal
131
Explain how polyadenylation occurs
CPSF binds to AAUAAA
CStF binds to GU-rich region and CPSF, forming a loop in the pre-mRNA
CFI and CFII stabilize it
PolyA polymerase (PAP) cleaves the strand 10-30 nts downstream of the AAUAAA
cleavage factors are released
PAP slowly begins to create a polyA tail (does not need a template)
PABII and other proteins bind to the nascent tail and this increases the speed of polyadenylation
PABII tells PAP to stop and it dissociates
Note: PABPs usually stay on the mRNA while it is exported to the cytosol and help protect it there
132
What is alternative polyadenylation?
one gene can have more than one polyadenylation site
can change the resulting protein
which signal is used depends on whether the factors are present and their affinity for the RNA
133
How are mRNAs often purified?
use polled primers attached to magnetic beads
| hold a magnet and wash out everything else
134
Explain RNA polyadenylartion in bacteria
PROMOTES mRNA degradation by the degradosome (polynucleotide phosphorylase and RNase E)
polyA tail changes the secondary structure and allows polynucleotide phosphorylase to bind to the 3' end
also recruits RNases
polyA tail is only ~30nt long
135
Describe RNA export to the cytoplasm
PABP promotes export from the nucleus and translation and inhibits degradation
mRNAs that aren't exported are degraded by the exosome
136
Which bases in RNA get deaminated? What do they pair with?
A to I, will pair with G
| C to U, will pair with A
137
How is ApoB RNA edited?
C to U by ApoBEC-1 in the small intestine at residue 2153 generates a stop codon, UAA
138
Where does splicing occur?
in the nucleus
| after it has been capped and polyadenylated and proteins that keep the pre-mRNA untangled have bound
139
What are longer, exons or introns?
introns
140
What is the 5' splice site consensus sequence?
Exon: AG
Intron: GUAAGU
141
What is the 3' splice site consensus sequence?
Intron: Py (8) -CAG
Exon: G --
there is also an A branch site near the pyrimidine-rich region, 10-50 bases from the splice site
142
Explain how the spliceosome works
U1 subunit binds to the GU at the 5' end of intron (contains nRNA base pairing with GU site)
U2 binds to A-branch site (through nRNA but not paired with the A)
complex brings the 5'GU to the pyrimidine-rich region
U4 and U6 snRNPs lock U1 and U2 in, are independent of the pre-mRNA sequence
U5 joins, the spliceosome is fully assembled which induces a conformational change and starts splicing
5' end is cleaved using ATP hydrolysis for energy
intron is looped back and 5' end and A-site form a new ester bond making the branch lariat structure
consensus sequence for the branch site is YNYRAY (y =pyr, r= pur)
3' end is then cleaved
ester bond between 3' end of intron and 5' end of exon exchanges for bond between the 2 exons
ligated exons are released, intron is still bound to spliceosome
lariat is released and degraded by a deb ranching enzyme
143
What is part of the spliceosome?
snRNPs and pre-mRNA
144
What is constitutive splicing?
every intron is removed and every exon is incorporated into the mature RNA
145
Where are self-splicing introns found?
note: they are ribozymes!
| in some bacteria and organelles
146
How do group 1 self splicing introns work? Where are they found?
protists, bacteria, bacteriophages
exogenous G is recruited
it does a nucleophilic attack on 5' exon/intron boundary
forms phosphodiester linkage with 5' end of intron
5' exon OH attacks 3' boundary linking the 2 exon
linear intron is released
147
How do group w self splicing introns work? Where are they found?
fungal and land plant mitochondria, algal plastids, bacteria, archaea
2'OH group of an intramolecular adenosine attacks 5' splice site and forms a lariat structure
freed 5' exon OH attacks 3' splice site
lariat intron is released
