transcription.translation lecture
TRANSCRIPT
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TRANSCRIPTION / TRANSCRIPTION / TRANSLATIONTRANSLATION
Take Notes on 17R
Transcription- process that makes mRNA from DNA
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The Central DogmaThe Central Dogma
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AP Biology 2007-2008
Transcription
fromDNA nucleic acid language
toRNA nucleic acid language
Only a specific part of DNA is Tx at one time, NOT the entire strand of DNA
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Beadle & Tatum 1941 | 1958
George Beadle Edward Tatum
Nobel Prize for their discovery that genes act by regulating definite
chemical events
one gene : one enzyme hypothesis
one gene : one polypeptide
Enzymes are polypeptides- updated findings are:
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Transcription
Making a single strand of mRNAtranscribed DNA strand = template stranduntranscribed DNA strand = coding strand
• same sequence as RNA
synthesis of complementary RNA strand at transcription bubble
Enzyme used: RNA polymerase
template strand
rewinding
mRNA RNA polymerase
unwinding
coding strand
DNAC C
C
C
C
C
C
C
C CC
G
GG
G
G G
G G
G
G
GAA
AA A
A
A
A
A
A A
A
AT
T T
T
T
T
T
T
T T
T
T
U U
5
35
3
3
5build RNA 53
Transcription
animation
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3 Processes of TranscriptionIn Nucleus1. Initiation
DNA unzipped into 2 separate strands by DNA Helicase.
Promoter region identified, Initiation Complex Made
2. Elongation
Free floating RNA NITROGEN BASES in the nucleus pair up w/unzipped DNA NITROGEN BASES by RNA Polymerase
Ex: DNA template: 3’ –C G T- 5’
3. Termination
Complement pairing is done at the end of gene
-a single strand of RNA is released
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Which gene will be Tx?1. Initiation
• Promoter region– binding site before beginning of gene
– TATA box catches attention
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At Promoter Region, Transcription Factors make Initiation Complex
• Initiation complex– transcription factors bind to promoter region
suite of proteins which bind to DNA turn on or off transcription
– trigger the binding of RNA polymerase to DNA
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2. ElongationMatching bases of DNA & RNA• Match RNA bases to DNA
bases on one of the DNA strands
U
A G GGGGGT T A C A C T T T T TC C C CA A
U
UU
U
U
G
G
A
A
A C CRNA
polymerase
C
C
C
C
C
G
G
G
G
A
A
A
AA
5' 3'
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3. TerminationRNA Polymerase reaches the end of the gene
and the RNA P, DNA, and new mRNA dissociate.
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mRNA Strand Needs Processing:
After Transcription
• In our DNA there are sequences that are not needed to make proteins.
• Due to complementing, these region end up in mRNA after Tx.
• These regions (aka=some junk)must be removed before Tl.
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Eukaryotic genes have junk= mRNA have junk!
• Eukaryotic genes are not continuous– exons = the real gene
expressed / coding DNA
– introns = the junkIn between sequence
eukaryotic DNA
exon = coding (expressed) sequence
intron = noncoding (inbetween) sequence
intronscome out of RNA!
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After TranscriptionmRNA ProcessingmRNA Processing
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After Transcription Review
Which mRNA sequences are removed?
Why are they removed?
mRNA Processing
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Result:Genetic code from DNA is transferred to
mRNA
The code obtained from DNA lets the mRNA know which amino acids to pick up:
• code is a set of 3 nitrogen bases = Codon
Overall Process of Transcription
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mRNADNA
RNAPolymerase
TranscriptionTranscriptionAdenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)
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AP Biology 2007-2008
Translation
fromnucleic acid language
toamino acid language
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TranslationTranslation• Process that converts mRNA into
protein
• Proteins are made of monomers of AA
• Tl occurs on ribosomes
• Where are ribosomes?
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Ribosomes Facilitates coupling of tRNA anticodon to mRNA codon
• organelle & enzyme!!
Structureribosomal RNA (rRNA) & proteins
2 subunits large small E P A
Protein synthesis/quiz
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Ribosomes
Met
5'
3'
UUA C
A G
APE
A site (acceptor site) • holds the newest tRNA carrying the next
amino acid to be added to chain
P site (peptidyl-tRNA site) • holds tRNA carrying growing polypeptide
chain
E site (exit site)• empty tRNA leaves ribosome
from exit site
Protein synthesis 2
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tRNA: remindertRNA: reminder
• tRNA = transfer RNA• picks up the correct amino acids
and carries them to the mRNA strand forming the protein
• Location of anticodon, the complement to the mRNA codon
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3 Steps of Translationmaking proteins
1. Initiation2. Elongation
3. Termination
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Building a polypeptideInitiationbrings together mRNA, ribosome subunits, initiator tRNA
Elongationadding amino acids based on codon sequence
Terminationend codon 123
Leu
Leu Leu Leu
tRNA
Met MetMet Met
PE AmRNA5' 5' 5' 5'
3' 3' 3'3'
U UA AAACC
CAU UG G
GUU
A AAAC
CC
AU UG GGU
UA
AAAC
CC
AU UG GGU U
A AACCA U UG G
G AC
ValSer
AlaTrp
releasefactor
AA A
CCU UGG 3'
How translation works
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Step 1: Initiationa)Ribosome attaches to the mRNA
b) Start codon is always AUG
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Step 2: Elongation
a) tRNA anticodon matches with codon on mRNA
b) Peptide bonds are formed between the AA
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Elongation (continued)
c) AA released from tRNA
d) Ribosome moves down the mRNA and continues adding AA
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Step 3: Terminationa)The ribosome reaches one of three stop
codons (UAA, UAG, UGA)b) The mRNA and protein (polypeptide chain) is
released
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The Decoder
This allows humans to translate the mRNA code into proteins
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There are 20 Amino Acids
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mRNA Start codon
Ribosome
Methionine
PhenylalaninetRNA
Lysine
Nucleus
TranslationTranslation
mRNA
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mRNACodon on
mRNA Translation direction
Amino AcidtRNA
tRNARibosome
Growing polypeptide chain
mRNA
Translation (continued)Translation (continued)
Anticodon on tRNA
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The Decoder
This allows humans to translate the mRNA code into proteins
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Prokaryote vs. Eukaryote genesProkaryotesDNA in cytoplasmcircular chromosomenaked DNAno intronsTx & Tl can occur simultaneously
EukaryotesDNA in nucleuslinear chromosomesDNA wound on histone proteinsintrons vs. exonstime & physical separation b/w Tx & Tl: ~1 hr from DNA to protein