Transcription in eukariotes by kk sahu

INTRODUCTION
A STRUCTURAL GENE
EUKARYOTIC RNAPs
MACHANISM OF TRANSCRIPTION IN EUKARYOTES:
- INITIATION
-ELONGATION
-TERMINATION
RNA SPLISING
DIFFERENT BETWEEN PROKARYOTIC & EUKARYOTIC TRANSCRIPTION
BIBLIOGRAPHY

1. TRANSCRIPTIONIN EUKARIOTES
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By
KAUSHAL KUMAR SAHU
Assistant Professor (Ad Hoc)
Department of Biotechnology
Govt. Digvijay Autonomous P. G. College
Raj-Nandgaon ( C. G. )

2. CONTENTS
•INTRODUCTION
•A STRUCTURAL GENE
•EUKARYOTIC RNAPs
•MACHANISM OF TRANSCRIPTION IN EUKARYOTES:
-INITIATION
-ELONGATION
-TERMINATION
•RNA SPLISING
•DIFFERENT BETWEEN PROKARYOTIC & EUKARYOTIC TRANSCRIPTION
•BIBLIOGRAPHY
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3. INTRODUCTION
Transcription, orRNA synthesis, is the
process of creating RNA, copy of a
sequence of DNA.
Both RNA and DNA are nucleic acids,
which usebase pairs
ofnucleotidesas acomplementary
language that can be converted from
DNA to RNA in the presence of the
correct enzymes.
During transcription, a DNA sequence is
read byRNA polymerase, which produces
a complementary,RNA strand.
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4. Astructural GENE
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5. •Exons:-Exons code for amino acids
and acid sequence of the protein
product. It is these portions of the
gene that are represented in final
mature mRNA molecule.
•Introns:-Introns are portions of the
gene that do not code for amino
acids, and are removed from the
mRNA molecule before translation.
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6. Control regions
•Start site:-A start site for transcription.
•A promoter:-A region a few hundred
nucleotides 'upstream' of the gene
(toward the 5' end). It is not transcribed
into mRNA, but plays a role in controlling
the transcription of the gene.
Transcription factors bind to specific
nucleotide sequences in the promoter
region and assist in the binding of RNA
polymerases.
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7. •Enhancers:-Some transcription factors
(called activators) bind to regions called
'enhancers' that increase the rate of
transcription. Some enhancers are
conditional and only work in the presence of
other factors as well as transcription
factors.
•Silencers:-Some transcription factors
(called repressors) bind to regions called
'silencers' that depress the rate of
transcription.
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8. Eukaryotic RNAPs
In bacteria, all mRNA is made from
the same RNA polymerase. However, in
eukaryotes, there are THREE DIFFERENT
RNA polymerases.
1.RNA Polymerase Isynthesizes rRNA.
2. RNA Polymerase IIsynthesizes all
PROTEIN CODING GENES,& mos tly
mRNA.
3. RNA polymerase IIIsynthesizes tRNAs
and also snRNAs (small nuclear RNAs) and
small cellular RNAs.
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9. Eukaryotic Transcription Initiation
•In eukaryotes, the initiation of transcription,
requires the presence of a
corepromotersequence in the DNA. Promoters
are regions of DNA which promote transcription
and are found around -10 to -35 base pairs
upstream from the start site of transcription. Core
promoters are sequences within the promoter
which are essential for transcription initiation.
RNA polymerase is able to bind to core promoters
in the presence of various specifictranscription
factors.
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10. •The most common type of core promoter in eukaryotes is a
short DNA sequence known as aTATA box. The TATA box, as
a core promoter, is the binding site for a transcription factor
known asTATA binding protein(TBP), which is itself a subunit
of another transcription factor, called Transcription Factor II
D(TFIID).
•One transcription factor, DNA helicase, hashelicaseactivity
and so is involved in the separating of opposing strands of
double-stranded DNA to provide access to a single-stranded
DNA template.
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11. Eukaryotic RNA ELONGATION
•In eukaryotes, the RNA is processed at both
ends before it is spliced.
•At the 5‘ end, a cap is added consisting of
a modified GTP (guanosine triphosphate). This
occurs at the beginning of transcription. The
5' cap is used as a recognition signal for
ribosomes to bind to the mRNA.
•At the 3' end, a poly(A) tail of 150 or more
adenine nucleotides is added. The tail plays a
role in the stability of the mRNA.
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13. Eukaryotic RNA TERMINATION
•Transcription termination in eukaryotes is less
understood but involves cleavage of the new
transcript followed by template-independent
addition ofAs at its new 3' end, in a process
calledpolyadenylation.
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14. m-RNA splicing
•Eukaryotic mRNAs are spliced by
complexes of small nuclear Ribonucleo-
Proteins (snRNPs).
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15. TRANSCRIPTION IN EUKARYOTES
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COMPLETE PROCESS: -
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17. DIFFERENT BETWEEN PROKARYOTIC & EUKARYOTIC
IN PROKARYOTES
•DNA dependent RNA
Polymerase-RNAPs.
•Promoter sequences-
TATpuATpu located -10 bp
of upstream.& TTGACA
Located -35 bp upstream.
•Post transcriptional
changes is none.
Transcription and
translation takes place
simultaneously.
•Transcription factors not
required.
IN EUKARYOTES
•DNA dependent RNA
Polymerase-I,II,III.
•Promoter sequences-TATA
boxLocated-30bp
upstream.& CAATbox
Located -70 to -80bp
upstream.
•Co transcription and
post transcription
change present.
•Transcription factors
required.
.
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18. BIBLIOGRAPHY
GENES IX;BenjaminLewin;JONES &
BartlettPublishers,2006.
CELL&MOLECULAR BIOLOGY, eighth
edition;E.D.P.DeRobertis,E.M.F.De
Robertis;PublishedbyB.I.WaverlyPvt
Ltd,NewDelhi,1995.
Sites:-
http://en.wikipedia.org/wiki/transcriptionin
eukaryotes.
http://tfiib.med.hardword.edu/transcription.
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