Transcript Gene expression powerpoint

Gene expression
Transcription and Translation
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1.
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Important Features
a. DNA contains genetic template for
proteins.
b. DNA is found in the nucleus
c. Protein synthesis occurs in the
cytoplasm - ribosome.
d. "Genetic information" must be
transferred to the cytoplasm where
proteins are synthesized.
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2. Processes of Protein Synthesis
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a. Transcription - genetic template for a
protein is copied and carried out to the
cytoplasm
b. Translation - template serves as a
series of codes for the amino acid
sequence of the protein
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Cells Use RNA to Make Protein
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The RNA Players – rRNA, mRNA, tRNA
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During polypeptide synthesis, ribosomal
RNA (rRNA) is the site of polypeptide
assembly.
Messenger RNA (mRNA) directs which
amino acids are assembled into
polypeptides.
Transfer RNA (tRNA) transports and
positions amino acids.
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Central Dogma of Gene Expression
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Transcription
– in the nucleus (if you have one)
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DNA sequence is transcribed into RNA
sequence
only one of two DNA strands (template or
antisense strand) is transcribed
non-transcribed strand is termed coding strand
or sense strand same as RNA (except T’s are
U’s)
In both bacteria and eukaryotes, the polymerase
adds ribonucleotides to the growing 3’ end of an
RNA chain.
 synthesis proceeds in 5’3’ direction
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(template runs 3’5’)
Transcription
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TATA box
– Signals beginning of section to be transcribed.
Transcription factor
– Binds to TATA box so that RNA polymerase can
then bind
Promoter
– Transcription starts at RNA polymerase binding
sites called promoters on DNA template strand,
which includes the TATA box and about 25 other
nucleotides that will not be transcribed.
Initiation
– Other transcription factors bind, assembling a
transcription initiation complex.
– RNA polymerase begins to unwind DNA helix.
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Transcription
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Elongation
– Transcription bubble moves down DNA at
constant rate leaving growing RNA strands
protruding from the bubble.
Termination
– Stop sequences, or terminators, at the end
of the gene cause phosphodiester bond
formation to cease, transcription bubble to
dissociate, and RNA polymerase to
release DNA.
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Transcription Bubble
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Transcription
Tell the story of transcription with your group –
one person starts: “First….,” and says one
sentence. The next group member picks up
where the first left off, and so on.
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RNA Processing
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In eukaryotes, RNA is modified after transcription
DNA sequence specifying a protein is broken into
coding segments (exons) scattered among longer
noncoding segments (introns).
– Small nuclear ribonuclearproteins (snRNPs)
associate with proteins to form spliceosomes.
Intron sequences are cut out of primary transcript
before it is used in polypeptide synthesis - they are
not translated
remaining exon sequences are spliced together to
form final processed mRNA
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RNA Processing
•5’ cap – G-P-P-P – protects mRNA from degradation
and serves as an “attach here” sign for ribosomes
•PolyA tail – A-A-A-A-A – inhibits degradation and
stabilizes mRNA as it moves out of nucleus
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RNA Processing
Each person in group tells one way that RNA
is modified after transcription in eukaryotes
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Now TRANSLATION!!!!
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Translation
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Begins when initial portion of mRNA molecule
binds to rRNA in a ribosome
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mRNA is in triplet code – 3 bases = codon
tRNA molecule with complimentary anticodon
binds to exposed codon on mRNA.
The codon determines which amino acid the
tRNA carries
AUG is always the start codon – it codes for the
amino acid Methionine (Met)
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Translation
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Elongation
– Once mRNA binds
to small subunit,
large subunit
attaches
– A site = where
tRNAs Arrive
– P site = where
Peptide bonds are
fomed
– E site = where
tRNAs Exit
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Translation
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Termination
– stop signal coded by one of three nonsense
codons: UAA - UAG – UGA
– Polypeptide released from ribosome
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Translation
Tell the story of translation with your group –
one person starts: “First….,” and says one
sentence. The next group member picks up
where the first left off, and so on.
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TC G TTC A AA
template
Strand
AG
T
T
C AAGT
U C G UU C A A A
mRNA
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A
A
TTC
G
A
C
T
template
Strand
AG
T
T
C AAGT
U C G UU C A A A
Nucleus
mRNA
Cytoplasm
Ribosome
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A
A
TTC
G
A
C
T
Template
Strand
AG
T
T
C AAGT
U C G UU C A A A
Nucleus
mRNA
Cytoplasm
U C G UU C A A A
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A
A
TTC
G
A
C
T
Template
Strand
AG
T
T
C AAGT
Nucleus
Cytoplasm
U C G UU C A A A
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A
A
TTC
G
A
C
T
template
Strand
AG
T
T
C AAGT
Nucleus
AA1
Cytoplasm
tRNA’s
AGC
U C G UU C A A A
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A
A
TTC
G
A
C
T
template
Strand
AG
T
T
C AAGT
Nucleus
ATP
AA1
•AA2
Cytoplasm
tRNA’s
AGC AAG
U C G UU C A A A
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A
A
TTC
G
A
C
T
Template
Strand
AG
T
T
C AAGT
AA1
Nucleus
ATP
AA1
•AA2
AA3
Cytoplasm
AAG U U U
U C G UU C A A A
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A
A
TTC
G
A
C
T
template
Strand
AG
T
T
C AAGT
AA1
Nucleus
AGC
AA1
•AA2
AA3
Cytoplasm
AAG U U U
U C G UU C A A A
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A
A
TTC
G
A
C
T
Template
Strand
AG
T
T
C AAGT
AA1
Nucleus
AGC
AA1
•AA2
AA3
Cytoplasm
AAG U U U
U C G UU C A A A
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A
A
TTC
G
A
C
T
Template
Strand
AG
T
T
C AAGT
AA1
Nucleus
AGC
AA1
•AA2
AA3
Cytoplasm
UUU
U C G UU C A A A
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The Genetic Code
1.A triplet code comprised of three nucleotide
bases in a sequence.
2.How many triplet codes?
20 common amino acids in a protein
4 diff. bases on DNA A,T,C, & G
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4 diff. bases on RNA U,A,G, & C
4 things put together in combinations of 3 =
43= 64
Therefore - 64 different DNA triplet codes or RNA
codons
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The 64 triplet codes
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60 code for amino acids
4 act as "stop" and "start codes
Degenerate Code- more than one
triplet code for some amino acids
e.g., GGG
GGU
GGC
GGA
All code for the
amino acid glycine
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