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Transcription and Translation (full version)
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12-3 RNA and protein synthesis
The Central Dogma
RNA and DNA
DNA• Double helix strands
• Deoxyribose
• A,T,C,G
• Nucleus
RNA• One strand
• Ribose
• A,U (uracil), C,G
• Cytoplasm & nucleus
Strands
Sugar
Base
Location
DNA ( A T C G)
RNA (A U C G)
A. messenger RNA (mRNA)B. transfer RNA (tRNA)C. ribosome RNA (rRNA)
Three types of RNA
A cooking book in French
A cooking book in Chinese
The Central Dogma
Steps from DNA to Proteins
Sequence of nucleotides
Sequence of nucleotides
Sequence of amino acids
Steps from DNA to Proteins
Nuclearmembrane
Transcription
RNA Processing
Translation
DNA
Pre-mRNA
mRNA
Ribosome
Protein
Transcription• Synthesize a mRNA molecule along one template
strand of DNA– In nucleus– Starts at promoter (TATA region of DNA)– Ends at terminator – Need enzyme RNA polymerase– When complete, pre-mRNA is released.
A T C G T A C G A A G T C T A C G G G A C T A T C G
T A G C G A T A G CA T G C T T C A G A T G C C C T
DNA
A C G A A G U C
mRNA
RNA polymerase
Direction of transcription
5 3
Transcription
• Steps– DNA unzipped by RNA polymerase– RNA polymerase builds RNA by base paring RNA
nucleotides to one strand of DNA– U is used instead of T– RNA is released and leaves the nucleus
Question
• What would be the complementary RNA strand for the following DNA sequence?
• DNA: GCGTATG
RNA: CGCAUAC
Question
• What is the enzyme responsible for the production of the RNA molecule?
• RNA Polymerase– Separates the DNA molecule by breaking the H-
bonds between the bases.
– Then moves along one of the DNA strands and links RNA nucleotides together.
RNA processing
RNA processing
mature mRNA transcript5’ 3’
3’
poly-A tail
5’snipped out intron snipped out intron
cap
transcription into pre-mRNA
Part of a DNA strand
exon intron exon exonintron3’ 5’
Translation
• Synthesize a polypeptide chain using the genetic code on mRNA
Translation
• Key characters– 1) mRNA : provide code– 2) tRNA : bring building blocks– 3) Ribosome (rRNA) : provide site
1) mRNA
• A linear sequence of nucleotides
• Three nucleotides make a codon – Codon : the genetic code
for a amino acid– 64 codons– AUG: start– UAA, UAG, UGA: stop
methionine glycine serine isoleucine glycine alanine stopcodon
protein
A U G G G C U C C A U C G G C G C A U A AmRNA
startcodon
Primary structure of a protein
aa1 aa2 aa3 aa4 aa5 aa6
peptide bonds
codon 2 codon 3 codon 4 codon 5 codon 6 codon 7codon 1
1) mRNA
2) tRNA
• Delivers amino acids to ribosomes
• One side attached with amino acid
• Another side with anticodon– Anticodon: 3 nucleotides
that can pair with a codon
– 20 different types of amino acids
amino acidattachment site
U A C
anticodon
methionine amino acid
2) tRNA
3) rRNA
• Major component of ribosomes
• Ribosome • Place where amino acids are
made into proteins• Small subunit + large subunit• Large subunit has 2 sites for
tRNA
PSite
ASite
Largesubunit
Small subunit
mRNA
A U G C U A C U U C G
Ribosome
3) rRNA
Translation
• Three Steps1. initiation: start codon (AUG)2. elongation:3. termination: stop codon (UAG, UAA, UGA)
• Let’s make a PROTEIN!!!!.
1) Initiation
PSite
ASite
Largesubunit
Small subunit
mRNA
A U G C U A C U U C G
1-tRNA
U A C
aa1
anticodon
codon
mRNA
A U G C U A C U U C G
2-tRNA
G
aa2
A U
Aanticodon
hydrogenbonds codon
1-tRNA
U A C
aa1
2) Elongation
mRNA
A U G C U A C U U C G
1-tRNA 2-tRNA
U A C G
aa1 aa2
A UA
anticodon
hydrogenbonds codon
peptide bond
3-tRNA
G A A
aa3
mRNA
A U G C U A C U U C G
1-tRNA
2-tRNA
U A C
G
aa1
aa2
A UA
peptide bond
3-tRNA
G A A
aa3
Ribosomes move over one codon
(leaves)
mRNA
A U G C U A C U U C G
2-tRNA
G
aa1
aa2
A UA
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
mRNA
A U G C U A C U U C G
2-tRNA
G
aa1aa2
A U
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
(leaves)
Ribosomes move over one codon
mRNA
G C U A C U U C G
aa1aa2
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
U G A
5-tRNA
aa5
mRNA
G C U A C U U C G
aa1aa2
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
U G A
5-tRNA
aa5
Ribosomes move over one codon
mRNA
A C A U G U
aa1
aa2
U
primarystructureof a protein
aa3
200-tRNA
aa4
U A G
aa5
C U
aa200
aa199
terminator or stop codon
3) Termination
4) End Product
• The end products of protein synthesis is a primary structure of a protein.
– A sequence of amino acid bonded together by peptide bonds.
aa1
aa2 aa3 aa4aa5
aa200
aa199
Question:
• The anticodon UAC belongs to a tRNA that recognizes and binds to a particular amino acid.
• What would be the DNA base code for this amino acid?
Answer:
• tRNA - UAC (anticodon)• mRNA - AUG (codon)• DNA - TAC