Translation

1
Translation
2
Translation

• ?????????????????????????????????? proteins
  (polypeptides) ????????????????? genes
  ????????????????????????????????????????????????
  (Central Dogma) ????
• ?????????????????????? (Gene expression)
  ?????????????

3
Transcription Translation ????Gene Expression
?? Prokaryote ??? Eukaryote
4

• ?????? ???? ?????? (Information/code) ??? gene
  ??? DNA ?????? (Transcription) ??????????? RNAs
  (mRNA, tRNA, rRNA)
• mRNA ?? information ????????????????????????
  (codons) ???????? ?????????? polypeptide
  (protein)
• tRNA ?? anticodon ??????? ????? amino acids
  ????????????? polypeptide ?????????? mRNA
• rRNA ??????? protein ?????????? Ribosome /
  ????????????????? proteins ????????

5
???????????????? Gene Expression ???? 2 ?????
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1. Messenger RNA (mRNA)

• ???????????????????????????????? translation
• ?????????????????
• Porkaryote ????????? Leader ?????????????
• Eukaryote ??? 5 cap ?????????????
• Coding region ????????????????? DNA ????????
  Codons ?????????
• Start ??? Stop codons ?????? ?????????????
  factors ????????????

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mRNA ??? Eukaryote
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Initiator ??? mRNA ?? Prokaryotic cells

• ????????????????? 5 ???????? Shine-Dalgarno
  sequence ???? ribosomal binding site ?????? 30S
  ribosome

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Initiator ??? mRNA ?? Eukaryotic cells

• ?? Cap ???? binding site ??? 40S subunit
• ?????? scan ????????
• 18S rRNA ????????
• Start codon
• ????????? Cap-binding protein ???? eIF3 ??? eIF4C
  ?????? ribosome ????

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Genetic CodeCodons

• Code ?? mRNA ???????? Codon
• 1 codon ?????????? 3 base ???????
• 1 amino acid
• 1 Code ?? 3 bases (triplet code) ??? 4 bases
• codes ??????? (4)3
• 64 codons

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??????????????? Codons
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• Condon ???? structural gene ??? code ???
  polypeptide ???????? Reading frame
• ?? 64 codons
• 1 start codon ????????????????? translation ???
  AUG ??? AUG ??????? code ??????? Methionine ??
  polypeptide
• 3 top codons ?????????? translation ???
• (1) UAA Ochre codon
• (2) UAG Amber codon
• (3) UGA Opal codon
• 60 codons ?????? amino acids ??? 19 ???

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(No Transcript)
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2. Transfer RNA (tRNA)

• tRNA ??????????????
• ?? secondary structure
• ??????? boot / cloverleaf ???? 3 stem loops
• D arm, Anticodon arm ??? T arm
• Anticodon arm ?? Anticodon ???????????? Codon
  ??? mRNA
• ???? 3 ????????????? amino acid

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Secondary structure ??? tRNA
16

• tRNA ???? translator ???? adaptor ??? amino acid
  ???????????????????? protein ???????????? mRNA ??
  ribosome
• tRNA ?????? amino acid ???? 2 ???????

17

• tRNA ??????????? ??? Prokaryote
• ??? methionyl-tRNAfMet ??????? tRNAfMet
• ????? formyl group ????????????????????? peptide
  bond ??????? amino group ??? carboxyl group
  ??????? 2 ??????? polypeptide

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• tRNA ??????????? ??? Eukaryote
• ??? methionyl-tRNAiMet ??????? tRNAiMet
• tRNA ????? methionine ???????? polypeptide
• ????????????? tRNAmMet ???? methionyl-tRNAmMet
  ?? methionine ??????
• polypeptide ?????????? ?????????
  ????????????????? polypeptide

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???????????????? Codon ??? Anticodon

• tRNAs decode ???????? mRNA ??????????????? base
  ??????? complementary bases ??????? tRNA ??? mRNA
• Francis Crick (1966) ?????
• 2 bases ?????? anticodon ?? complement ???????
  codon
• base ?????? 3 ??? anticodon ??????
  non-complementary base ??? codon

20

• ????? tRNA 1 ??? ?????? amino acid
  ??????????????? ?????? ???? codons ??? ????????
  Wobble Effect
• 60 codons ?????????? ??? 19 amino acids

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3. Ribosome
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rRNAs ?? Ribosomes

• Prokaryote
• 70S ribosome
• 30S subunit
• 16S rRNA
• 50S subunit
• 23S 5S rRNAs
• S Swedberg unit ?????????? ?????

• Eukaryote
• 80S ribosome
• 40S subunit
• 18S rRNA
• 60S subunit
• 28S, 5.8S, 5S rRNAs

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• Ribosome ???? 2 subunit ??????????????????????? 3
  codons ???? 3 sites
• A site ???? Aminoacyl site ?????? aminoacyl-tRNA
• P site ???? Peptidyl site ?????? tRNA ????
  peptide
• E site ???? Exit site ?????? free tRNA
• ???????????? ???????????????? ribosome

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(No Transcript)
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• Mechanism of Translation
• 1. Initiation
• 2. Elongation
• 3. Termination

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1. Initiation of Translation ???????????

• 1. Initiation factor (IF) ?????? small subunit
  ???ribosome
• 2. Small subunit ribosome-IF ?????? mRNA
• 3. First aminoacyl-tRNA ???????? ribosome ???
  Psite ?????????? AUG
• 4. Large subunit ribosome, IF, ??? GTP ??????
  small subunit ribosome complex
• 5. GTP --gt GDP ??? IF ??????? --gt initiation
  ???????

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Initiation processProakryote

• 30S subunit ribosome ?????? IF-3 ??? mRNA
• methionyl-tRNAfMet ?????? IF-2 ????????????
  ribosome ??? P site

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2. Elongation of Translation

• ???????????????? prokaryote ??? eukaryote
  ?????????
• 1. Aminoacyl-tRNA ???????????????????? A site ???
  ribosome
• 2. tRNA ??? P site ???? (transfer) polypeptide
  chain ???????? amino acid ??? tRNA ??? A site
  ???? peptide bond

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?????? amino acids
Amino acid
Dipeptide
Polypeptide
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• 3. Ribosome ?????????? (translocate) 1 codon ??
  mRNA ???????? A site ????
• 4. A site ??????????????? P site ???? ???
• P site ??????????????? E site
• 5. Free tRNA ???? (????? amino acid) ??? E site
  ????????????? ribosome

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• Elongation of translation
• Elongation factors ???
• EF-Ts,
• EF-Tu (eEF1),
• GTP ???
• EF-G (eEF2)

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3. Termination of Translation

• ??????? Stop codon 1 ?? 3 ?????????????
• Release factors (RFs) ??????????????? stop codons
  ???
• ????? tRNA ???? stop codons ???

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• ????? elongation ????? stop codon ?? ? ??? 1?? 3
  stop codons ???????? A site
• Release factors (RFs) ???????????? stop codon
• RFs ????????? peptidyl transferase ?????? H2O
  ??????? carboxyl end ??? polypeptide
• Polypeptide ?????????? tRNA ??????????? P site
• free tRNA ???????????? E site ?????? ribosome
  --gt ???? translation

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• Termination in
• Prokaryote
• ?? 2 RFs ???
• RF-1 ??? UAA
• ??? UAG
• RF-2 ??? UAA
• ??? UGA
• Eukaryote ?? RF
• ?????

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Polyrisome ?? prokaryotic cells

• ?? prokaryotic cells
• Translation ??? ???? ribosome ??????????
  mRNA?????
• ????? initiation ?? mRNA ?????? ribosome
  ?????????????
• Translation ???????? ??? ribosome ???????
  ??????????????
• ??????????? cycles ??? Translation ??????
  ribosomes ????????? polyribosome ?????? mRNA
  ?????????????????? polypeptide

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Polyribosome
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(No Transcript)