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8/2/2019 Lecture03 01 P24 RNA Synthesis
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Lecture 03/ 01P24
RNA SYNTHESI S
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Just one of t he DNA st rands for a gene
called the templatestrand.
molecule need not use t he same st rand
as the tem late. RNA polymerase is t he enzyme that
uses DNA as a t em late t o make RNA.
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I nit iat ion of t ranscript ion requires t hatRNA ol merase reco nize and bind
t ight ly, apromotersequence on DNA.
Bindin can be inf luenced b other
proteins. The romoter se uence direct s t he RNA
polymerase as t o w hich of t he t w o
st rands is t he template and t herefore inw hat direct ion t he RNA polymeraseshould move.
See Figures Figure 14.7 Part 2 and 14.4 Part 1
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.
Part 1
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.
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.
Part 2
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,t he DNA about 10 base pairs at a t ime
init iat ion sit e) in t he 3 - to-5 direction.
t he 5 to 3 direct ion; i.e. t he RNAa sc p s a pa a e o etemplat e st rand.
See Figure 14.4 Part B
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.
Part 3
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,aw ay, allow ing the already t ranscr ibed
helix.
e energy or syn es s comes rom
the removal and breakdow n of t hepyrop osp ate group rom eacnucleoside t r iphosphate building block
added. (See Figure 11.21 Part a, Edn 7)
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Figure 11.21 Sequencing DNA
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art icular base se uences
ar cu ar ase sequences n eDNA specify t erminat ion.
I n eukaryotes, t he process
does not occur unt il a sequence
polyadenylat ion has been
transcribed (See Figure 14.4 - Part C)
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Part 3
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There are t hree major classes of RNA: essenger m - co es or a
protein
Ribosomal RNA ( rRNA) - cont ribut es t ost ructure and funct ion of r ibosomes(protein synt hesis machinery)
Transfer RNA t RNA carr an aminoacid and act as an adapt or moleculeallow in decodin of mRNA to rotein
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Prokaryot es have one type of RNA,
t RNA, and rRNA
polymerases: I , I I , and I I I .
eukaryotes.
-RNA polymerases occur for every 104
t o 105 bases incor orated.
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DNA codes for RNA by t ranscr ipt ion.
nucleot ides (codons) . Since t here are
possible codons.
.
The 64 possible codons code for only
signals found in all mRNA molecules.
See Figure 14.6
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.
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One mRNA codon, AUG ( t he start
codon) , indicates t he start ing point oft ranslat ion and codes for methionine.
and AUG must t herefore be used w hen amet hionine occurs w it hin a prot ein.
Three stopcodons (UAA, UAG, and
reading the mRNA; t hat is, t hey.
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After subt ract ing start and stopco ons, t e rema n ng co onscode for 19 di f ferent amino acids.
This means t hat many amino.
Thus t he code is redundant.
. .
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The code is not ambiguous. Each codon,t w o or t hree possible amino acids.
e genet c co e s near y un versa ,applying t o all species on our planet .
Minor variat ions are found w it hin
mit ochondr ia and chloroplast s; otherexcept ions are few and slight .
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u aryot c un e pro aryot cDNA) , is separated f rom the
cytoplasm by being contained w it hina nucleus.
The init ial mRNA t ranscr ipt of t he
DNA is modif ied rocessed beforeit is export ed to t he cytoplasm.
ev ew gure . art
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.
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After t ranscr ipt ion, t he pre-mRNA is
-G cap at t he 5 end and a poly A t ail
t he AAUAAA sequence).
t he stabilit y of t he RNA and for it s
Review Fi ure 14.10
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The int rons are removed from t he mRNA,of RNAs and proteins.
s soon as t e pre-m s t ranscr eseveral small nuclear r ibonucleoprot einpart c es sn s n
This links all t he coding regions t ogetheras a cont inuous sequence.
.
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.
Machine
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be cont rolled at t he:
,
posttranscriptional,
t ranslat ional, and
.
.
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Ex ression Part 1
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Ex ression Part 2
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Ex ression Part 3
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e ma or me o o con ro s se ec ve
t ranscript ion, w hich result s from specif ic prot eins
t ranscri t ion factors bindin t o re ulat orregions on DNA.
Specific t ranscript ion fact ors must bind t o t hepromoter e ore po ymerase can n .
A group of general t ranscript ion factors
w ork w it h RNA polymerase I I t o t ranscribe
mRNAs I nit iat ion also depends on t he proteins bound(act ivators and repressors) .
Review Figures 16.14 and 16.15
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.
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., ,
Activators
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The simult aneous cont rol ofw e y separate genes spossible t hrough proteins t hat
bind t o common sequences in
Review Figure 16.17
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.
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Some 50% of eukaryot ic genesgenera y ave severa exons analternativesplicing can be used t o
produce dif ferent prot eins.
Review Figure 16.22
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.
Mature mRNAs and Proteins
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The stabili t y of mRNA in t hecytop asm can e regu ate ythe binding of proteins.
Specif ic AU-r ich sequences mark
by a ribonuclease complex ( t heexosome
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ene expression
One class are microRNAs miRNAs- short , 19-25 nucleot ide, non-codin RNAs
Some miRNAs bind complement ary
and prevent t heir t ranslat ion and
.
ev ew gure .
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.
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ene ex ression
t he human genome is st i l l unknow n;current est imat es ran e from 500
1000 -
genes; t hus on average each miRNA
might regulate about 200 t arget genes Many genes have target sit es for a few
dif ferent miRNAs
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miRNAs appear t o be de-regulated in in several
including chronic lymphocytic leukemia, pediat ric
Burki t t s lymphoma, gast ric cancer and lung cancer
The miR-17-92 miRNA clust er on chromosome 13is fr equent ly ampl if ied in B-cell lym phomas
Elevated levels of t hese miRNAs are found inclinical samples and in related cell lines
When t hese miRNAs are overexpressed in amouse model cancer resul t s
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Conf irm that many miRNAs are t issue-
s ecif icall ex ressed Potent ial for diagnost ic use:
-
- dist inguishing bet w een relat ed cancers
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Oft en t here is lit t le correlat ion bet w eene a ou o a e a ou o
protein synthesized.
be determined by factors act ing aft er
. One w ay is binding of repressor proteins t o
.
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Regulat ion of protein longevit y:
modified aft er t ranslat ion.
w ay to cont rol it s act ions.
l inked to a 76-amino acid prot ein,
. Other ubiquit in chains t hen at t ach t o the
.
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The prot einubiquit in complex t hen binds
.
I nside the proteasome, energy f rom ATPs use o cu o e u qu o
recycling) and unfold it s t argeted protein.
Proteases digest t he protein int o smallpept ides and amino acids.
.
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