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TRANSLATIONINTRODUCTION
Protein (amino acid polymer, N terminus, C terminusRibosomes: 30 S subunit plus 50 S subunit form functional 70 S ribosomemRNA is read 5' to 3'Initiation Codons; Stop CodonsPolysomes
INITIATIONInitiator tRNA (N - formyl methionyl tRNA) Initiation complex
ELONGATIONPeptidyl transferaseA, P, E sites on ribosome
TERMINATIONStop codons
SHINE-DALGARNO
2
3AMIDES
ACID
AMINE
AMIDE
PEPTIDE BOND
PEPTIDE-AMIDE FORMED BETWEEN TWO AMINO ACIDS: ALANYL-GLYCINE
MONO SUBSTITUTED DISUBSTITUTED
4
5'
3'
3'
5'
TRANSCRIPTION
TRANSLATION
UNTRANSLATED REGION
5' 3'
N CCODENOBELHOLLEY
NIRENBERGKHORANA
[STOP CODONS = UAA/UAG/UGA]
GENEPROMOTER
+1
5RIBOSOMES - NON-SPECIFICTRANSLATE ANY MESSAGEPROKARYOTIC
70S 50S + 30SSUBUNITS
COMPOSITION 50S 30S
NUMBER OF DIFFERENT PROTEINS 34 21
NUMBER OF DIFFERENT rRNA MOLECULES
ONE - 5SONE - 23S ONE 16S
POLYSOMES
6
CODON FOR PHENYLALANINE
tRNA - IS AN ADAPTER - ADAPTS AMINO ACID AND CODON
ANTICODON3' 5'
mRNA
5' 3'
TRANSFER RNA tRNA ~ 60EACH SPECIFIC FOR 1 AMINO ACID AND 1 CODON
HO5'
3'
tRNAPHE
SPECIFIC FORPHENYLALANINE
8OVERALL:
AMINO ACID + ATP + tRNA AMINO ACYL-tRNA + AMP + PPiSTEP 1:
NUCLEOTIDYLTRANSFER
PPi
AMINO ACID + ATP AMINO ACYL-AMP + PPiAMINO ACID ACTIVATING ENZYME =
AMINO ACYL~tRNA SYNTHETASE
+
ANHYDRIDE
7GENETIC CODE IS DEGENERATE -
DIFFERENT TRIPLETS ENCODE THE SAME AMINO ACID
"WOBBLE" MEANS THAT SOME SPECIFIC tRNAs CAN READ MORE THAN ONE CODON
"WOBBLE" MAKES IT POSSIBLE FOR AN ORGANISM TO TRANSLATE ALL 61 CODONS WITH FEWER THAN 61 tRNAsPROKARYOTES OFTEN HAVE 60 - 80 tRNAs
SOME DIFFERENT tRNAs CARRY THE SAME AMINO ACIDSSOME HIGHLY SPECIALIZED PROKARYOTES HAVE ~ 40
tRNA GENES
ACAACGACCACU
ALL CODE THREONINE
A THREONINE tRNA WITH AN ANTI-CODON OF3' UGG 5'
5' ACC 3'5' ACU 3'
PAIRS WITHOR THREONINE
9
FORMYL METHIONINE~tRNA[SPECIFIC FOR STARTING TRANSLATION]
INITIATING TRANSLATION
METHIONINE + tRNAfMET
+ ATP+ ACTIVATING ENZYME
fMET
METHIONYLtRNAfMET
fMET
FORMYLGROUP
[FOLIC ACID]
N-FORMYL METHIONYL
~tRNAfMET
10INITIATION COMPLEXES
F MET
F MET
pppG5' 3'
mRNA + 30S + F - MET~tRNAfMET
+ GTP + INITIATION PROTEINS
30S SUBUNIT30S INITIATION
COMPLEX
50S SUBUNIT
E P A
mRNA
EXITPEPTIDYL
ACCEPTORpppG 3'
70S RIBOSOME
11
PEPTIDYL TRANSFERASE
F-METSER
F-MET SER TYR
P A
ELONGATION-POLYMERIZATION
[CHLORAMPHENICOL]
5' G
5' G
3'
3'P A
12
TRANSLOCATION [ERYTHROMYCIN – INHIBITS MOVEMENTAMINO ACYL TRNA FROM A SITE TO P SITE, BLOCKS ELONGATION;AZITHROMYCIN]
F-METSER TYR
P A5' 3'
P A
TYRF-MET
SER
5' 3'
HO
HO
E
13
P
TYRF-MET SER
5'
HO
AE
GLNHO
GUC
ALL INHIBIT 30S RIBOSOME FUNCTION
TETRACYCLINE – INHIBITS AMINO ACYL TRNA BINDING A SITEDOXYCYCLINE - NEWER
STREPTOMYCIN - TRNA MISMATCHING, MIS-TRANSLATION SPECTINOMYCIN - BINDS 30S SUBUNIT; EXACT MECHANISM ?
15HOW DO RIBOSOMES KNOW WHERE TO START
TRANSLATING?
A. HOW TO DISTINGUISH INITIAL AUG FROM INTERNAL AUG
B. HOW TO RECOGNIZE SEVERAL INITIATING AUG's IN ONE mRNA
AUG
AUG UAA5' 3'
PROTEIN CODING REGIONINTERNAL AUG
UNTRANSLATEDREGION
5' 3'AUG
AUG
1st CODINGREGION
2nd CODINGREGION
3rd CODINGREGION
AUG
POLY CISTRONIC mRNA RIBOSOMES TRANSLATE ALL THREE INDEPENDENTLY.
HOW?
16
PROTEIN CODING REGIONS ARE PRECEDED BY SHINE-DALGARNO SEQUENCES [PROKARYOTES]
5' 3'
5'
CODING REGION
AUGCODING REGION
~ 7+1
SHINEDALGARNO
SHINE DALGARNO SEQUENCES:
SHINE
DALGARNOSHIN
E
DALGARNO
AUG
17
30S SUBUNIT
SITES
BINDING BETWEEN SHINE-DALGARNO AND rRNA (16S) POSITIONS mRNA SO THAT AUG
OCCUPIES P SITE
18
mRNA
PROTEINSRIBOSOMES
REPLICATION, TRANSCRIPTION & TRANSLATION - DYNAMIC
THEY ALLGO ON ATTHE SAME
TIME !
19RIBOSOMES ARE RIBOZYMES - THE ACTIVE SITE FOR CATALYZING PEPTIDE BOND
FORMATION IS ENTIRELY RNA
23S rRNA IS PEPTIDYL TRANSFERASEADENINE [#2451] PARTICIPATES IN FORMING PEPTIDE
BONDSADENINE #2451
H BOND
ADENINE N3 TAKES PROTONNITROGEN ATTACKS
APPRECIATE !
CHLORAMPHENICOLBINDS A 2451 &A 2452 - INHIBITS
20
H BOND STABILIZES
INTERMEDIATE
tRNA OXYGEN TAKES PROTONtRNA PEPTIDE BOND BREAKS
OXYANION ELECTRONS FORM C O
APPRECIATE !
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