Ch. 10 – From DNA to Protein - Quia Biology! Ch. 10 – From DNA to Protein AP Biology! Protein...
Transcript of Ch. 10 – From DNA to Protein - Quia Biology! Ch. 10 – From DNA to Protein AP Biology! Protein...
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Metabolism and Gene Expression n Inheritance of metabolic diseases suggests that genes
coded for enzymes
n Diseases (phenotypes) caused by non-functional gene product (Tay-sachs, PKU (phenylketonuria), albinism)
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RNA vs. DNA
RNA DNA
Single strand
Double strands
Ribose Deoxyribose
Uracil (U) Thymine (T)
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Transcription n the formation of a
specific RNA sequence from a specific DNA sequence
n requires: - a DNA template - nucleoside
triphosphates (ATP, GTP, CTP, UTP) as substrates
- RNA polymerase
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§ RNA polymerase binds only to promoter.
§ TATA box § Transcription factors
(proteins) help RNAP to bind.
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§ RNAP moves along the DNA template from 3’ to 5’
§ RNAP adds complementary nucleotides to the growing mRNA.
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Transcription
Transcription Animation http://bcs.whfreeman.com/hillis1e/
#667501__674147__
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Eukaryotic DNA has “junk”
n Exons – (expressed/coding) segment of DNA
n Introns – in-between (non-coding) sequence
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RNA splicing enzymes
Not smurfs! “snurps”
n snRNPs (small nuclear ribonucleoproteins)
n Spliceosome - snRNPs binds to
consensus sequences
- cut and paste gene
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Alternative RNA splicing n different segments treated as exons
Defining a gene is getting more complicated!
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A A mRNA
5'
3'
G P P P
50-250 A’s
More post-transcriptional processing n Adding 5ʹ′ GTP cap and poly-A tail: - protects mRNA on its trip from nucleus to cytoplasm
from (hydrolytic) enzymes in cytoplasm - facilitates binding of RNAP
n Neither 5’ cap and poly-A tailget translated into proteins
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AUGCGUGUAAAUGCAUGCGCC!mRNA
mRNA codes for proteins in triplets
TACGCACATTTACGTACGCGG!DNA
AUGCGUGUAAAUGCAUGCGCC!mRNA
Met Arg Val Asn Ala Cys Ala!protein
?�
codon
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Cracking the Code
Animated Tutorial 10.3 – Deciphering the Code http://bcs.whfreeman.com/hillis1e/
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The Code n is the code for ALL
life!
n strongest support for a common origin for all life
n redundant (several codons for each amino acid) but not ambiguous (code for the different amino acids)
n 3rd base (3’ end) “wobble”
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Transfer RNA structure n “Clover leaf” structure n anticodon on “clover leaf” end, amino acid
attached on 3ʹ′ end
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Charging tRNA n Aminoacyl-
tRNA synthetase bonds amino acid to tRNA
n Energy is required
n ATP → AMP
n bond is unstable so it can release amino acid at ribosome easily
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Ribosomes n A site (aminoacyl-tRNA) holds tRNA carrying next
amino acid to be added to chain
n P site (peptidyl-tRNA) holds tRNA carrying growing polypeptide chain
n E site (exit) empty tRNA leaves ribosome from exit site
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Building a polypeptide n Initiation brings together
mRNA, ribosome subunits, initiator tRNA
n Elongation adds amino acids based on codon sequence
n Termination adds end codon
1 2 3
Leu
Leu Leu Leu
tRNA
Met Met Met Met
P E A mRNA 5' 5' 5' 5'
3' 3' 3' 3' U U A A A A C
C C
A U U G G G U U
A A A A C
C C
A U U G G G U U
A A A A C
C C
A U U G G G U U A A A C
C A U U G G
Val Ser Ala Trp
release factor
A A A
C C U U G G 3'
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Protein Synthesis
Animated Tutorial 10.4 – Protein Synthesis http://bcs.whfreeman.com/hillis1e/
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Initiation
n small ribosomal subunit binds to mRNA recognition sequence
n Methione-charged tRNA binds to AUG.
n Large subunit joins
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Elongation n Second tRNA enters A
site n Bond breaks between
tRNA in P site and its amino acid
n peptide bond forms between that amino acid and the amino acid on tRNA in A site
n First tRNA moves to E site, dissociates from complex
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Elongation
n Elongation occurs as the steps are repeated, assisted by elongation factors.
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Elongation
n a stop codon enters A site
n Stop codon binds a protein release factor
n Polypeptide chain separates from the ribosome
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Can you tell the story?
DNA
pre-mRNA
ribosome
tRNA
amino acids
polypeptide
mature mRNA
5' GTP cap
poly-A tail
large ribosomal subunit
small ribosomal subunit
aminoacyl tRNA synthetase
E P A
5'
3'
RNA polymerase
exon intron
tRNA
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Protein Synthesis in Prokaryotes
Bacterial chromosome
mRNA
Cell wall
Cell membrane
Transcription
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Prokaryote vs. Eukaryote genes n Prokaryotes - DNA in cytoplasm - circular chromosome - naked DNA - no introns
n Eukaryotes - DNA in nucleus - linear chromosomes - DNA wound on
histone proteins - introns vs. exons
eukaryotic DNA
exon = coding (expressed) sequence
intron = noncoding (inbetween) sequence
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n Transcription and translation are simultaneous in bacteria
n DNA is in cytoplasm
n no mRNA editing
n ribosomes read mRNA as it is being transcribed
Translation in Prokaryotes