Lecture03 01 P24 RNA Synthesis

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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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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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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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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., ,

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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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

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ev ew gure .


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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:

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- 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

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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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Lecture03 01 P24 RNA Synthesis

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