Upload
stella
View
38
Download
0
Embed Size (px)
DESCRIPTION
Transcription. Gene 2. DNA molecule. Gene 1. Gene 3. DNA strand (template). 5. 3. A. C. C. T. A. A. A. C. C. G. A. G. TRANSCRIPTION. A. U. C. G. C. U. G. G. G. U. U. U. 5. mRNA. 3. Codon. TRANSLATION. Gly. Phe. Protein. Trp. Ser. Figure 17.4. - PowerPoint PPT Presentation
Citation preview
Figure 17.4
DNAmolecule
Gene 1
Gene 2
Gene 3
DNA strand(template)
TRANSCRIPTION
mRNA
Protein
TRANSLATION
Amino acid
A C C A A A C C G A G T
U G G U U U G G C U C A
Trp Phe Gly Ser
Codon
3 5
35
A codon in messenger RNA Is either translated into an amino acid or serves as a
translational start or stop signal
Figure 17.5
Second mRNA baseU C A G
U
C
A
G
UUUUUCUUAUUG
CUUCUCCUACUG
AUUAUCAUAAUG
GUUGUCGUAGUG
Met orstart
Phe
Leu
Leu
lle
Val
UCUUCCUCAUCG
CCUCCCCCACCG
ACUACCACAACG
GCUGCCGCAGCG
Ser
Pro
Thr
Ala
UAUUAC
UGUUGCTyr Cys
CAUCACCAACAG
CGUCGCCGACGG
AAUAACAAAAAG
AGUAGCAGAAGG
GAUGACGAAGAG
GGUGGCGGAGGG
UGGUAAUAG Stop
Stop UGA StopTrp
His
Gln
Asn
Lys
Asp
Arg
Ser
Arg
Gly
UCAGUCAGUCAGUCAG
Firs
t mR
NA
bas
e (5
end
)
Third
mR
NA
bas
e (3
end
)
Glu
The following is the sequence of a bases on the template strand of DNA in the transcription unit
3’ – GGATCAGGTCCAGGCAATTTAGCATGCCCC – 5’
a) Transcribe this sequence into mRNA
b) List the order of amino acids
Four Major Steps1. Initiation
2. Elongation
3. Termination
4. Posttranscriptional Modification
Parts of a Genepromoter - DNA sequences which indicate the
location of a gene
promoters are located upstream from the DNA region that contains the information to be transcribed into mRNA
promoter transcription region termination sequence
gene
Orientation About a Gene
RNA polymerase – transcription enzyme (synthesizes mRNA in 5’ 3’ direction)
uses upstream, promoter region to determine where to start mRNA transcription
0positive numbersnegative numbers
upstream downstream
start transcription
InitiationdsDNA (double stranded DNA) needs to be opened
for mRNA to be made
promoter regions are often sequences of A’s and T’s2 H-bonds between A&Teasier to break than 3 H-bonds between G&Cprokaryotic genes have a TATA box
RNA polymerase opens the dsDNA
Initiation
transcription factors - numerous protein factors are involved in starting transcription
some of these proteins help control how often genes are transcribed
Figure 17.8
TRANSCRIPTION
RNA PROCESSING
TRANSLATION
DNA
Pre-mRNA
mRNA
Ribosome
Polypeptide
T A T A AA A
A T A T T T T
TATA box Start point TemplateDNA strand
53
35
Transcriptionfactors
5
3
3
5
Promoter
53
3
55
RNA polymerase IITranscription factors
RNA transcript
Transcription initiation complex
Eukaryotic promoters1
Several transcriptionfactors
2
Additional transcriptionfactors
3
Elongation
RNA polymerase synthesizes mRNA in the 5’ 3’ directionno primer is
necessary
template strand - only one strand of the DNA is transcribed
Elongation
RNApolymerase
Non-templatestrand of DNA
RNA nucleotides
3 end
C A U C C A AU
T A G G T TA
AC
G
G
AT
CA
T C C A A TT
GG
3
5
5
Newly madeRNA
Direction of transcription(“downstream”) Template
strand of DNA
Elongation Nomenclature
the template strand is copied into mRNA strand also known as the antisense strand
5’ A T T A C G A T C T G C A C A A G A T C C T 3’
5’ A U U A C G A U C U G C A C A A G A U C C U 3’
3’ T A A T G C T A G A C G T G T T C T A G G A 5’
SENSE STRANDANTISENSE STRAND
DNA
mRNA
TerminationRNA polymerase stops transcribing once it reaches
the termination sequenceenzyme dissociates with DNA strand and binds to
another promoter sequence
termination sequences differ between prokaryotes and eukaryotes
Transcription
Transcription Animation
http://www.youtube.com/watch?v=WsofH466lqkStart watching at 1:30.
Transcription
Figure 17.7
PromoterTranscription unit
RNA polymerase
Start point
53
35
35
53
53
35
53
35
5
5
Rewound
RNA
RNA
transcript
3
3
Completed RNA transcript
Unwound
DNA
RNA
transcript
Template strand of DNA
DNA
1 Initiation. After RNA polymerase binds to the promoter, the DNA strands unwind, and the polymerase initiates RNA synthesis at the start point on the template strand.
2 Elongation. The polymerase moves downstream, unwinding theDNA and elongating the RNA transcript 5 3 . In the wake of transcription, the DNA strands re-form a double helix.
3 Termination. Eventually, the RNAtranscript is released, and the polymerase detaches from the DNA.
Posttranscriptional Modification mRNA of eukaryotic cells need to be modified before
moving into the cytoplasm
primary transcript – initial eukaryotic mRNA transcript, before modification
1. 5’ cap – 7-methylguanosine triphosphate2. poly-A tail – approx. 200 adenine ribonucleotides are
added at the end
modifications prevent cellular enzymes from breaking down mRNA before it is translated into protein
5’ 3’
5’ cap added by capping enzyme complex
primary transcript
3’ poly-A tail added by poly-A polymerase
AAAAAAA
mG
mG
Modifications: Introns / Exonseukaryotic genes are longer than prokaryotic
geneswe carry extra “junk” DNAmost of this “junk” DNA signals when and how often
genes should be transcribed regulatory DNA
primary transcript is longer than necessaryexons – RNA sequences that will be expressed; helps
makes the proteinintrons – interfering RNA sequences; need to be
removed before translation
AAAAAAAmGexon exon exonintron intron intron intron
introns removed by spliceosome proteins
AAAAAAAmGexon exon exon
mRNA transcript
Spliceosome ComplexSpliceosomes are a series of small
nuclear ribonucleoproteins (snRNP) that work together to remove introns.
snRNPs recognize specific sequences on the intronscuts out intron sequencessplices exon sequences together
RNA transcript (pre-mRNA)Exon 1 Intron Exon 2
Other proteinsProteinsnRNA
snRNPsSpliceosome
Spliceosomecomponents
Cut-outintronmRNA
Exon 1 Exon 2
5
5
5
1
2
3
Classwork/HomeworkSection 5.3 – pg. 249 #1-5, 7-9