Translation of the Genetic Message Flashcards
Overview of translation
AA are activated and fused to tRNA
Aminoacyl-tRNA combines with ribosomes and mRNA
AA are joined in the ribosome to make a polypeptide in the order specified by the mRNA sequence
the polypeptide chain is terminated
What part of the ribosome catalyzes formation of peptide bond between growing polypeptide and incoming AA
large subunit
How are 4 bases of DNA and RNA decoded into protein
Adaptor hypothesis
Translation requires
mRNA-contains the codons
tRNAs-contains the anticodons
- 3’ end of tRNA carries a specific AA
Ribosome
Ribosomal RNA makes up what percentage of RNA
85%
Three types of RNA used in protein synthesis
rRNA
tRNA
mRNA
An AA gets matched to tRNA by a
tRNA synthetase
forms a covalent bond
the aminoacylation has two steps and requires
free energy from ATP
Two steps of aminoacyl-tRNA synthetase reactions
activation of AA- reacts with ATP to form aminoacyl-adenylate- irreversible step
conjugation of AA to ribose of 3’ adenylate of tRNA- forms an aminoacyl-tRNA and AMP
What is the irreversible step of aminoacyl-tRNA synthetase reaction
activation of AA
Amino acid + tRNA + ATP ->
aminoacyl tRNA + AMP + PPi
the genetic code is read by tRNA molecules in sets of three consecutive nucleotides in mRNA called a
codon
Each codon specifies
one particular AA used in a protein
Codon triplet is
non-overlapping
comma-less
degenerate
universal
Reading frame is
important
3 bases-codon
Start codon
AUG methionine
Stop codons
UAA
UAG
UGA
Many codons are
degenerate or redundant
two or more codons may code for
the same AA
How is degeneracy of the code possible with base pairing
certain tRNAs can recognize more than one codon because of adaptable hydrogen bonding
wobble
adaptability of tRNAs to recognize more than one codon
The wobble base is in which position
5’ position of the anticodon
Chain initiation in prokaryotes requires
fmet-tRNA
initiation codon of mRNA
30s ribosomal subunit
50s ribosomal subunit
initiation factors IF-1, IF-2, and IF-3
GTP, Mg 2+
Summary of translation initiation in E. coli
- mRNA and fMEt-tRNA in complex IF-2-GTP bind to the small ribosomal subunit
2.association of large subunit with 30s triggers IF-2 to hydrolyze its bound GTP
- tRNA bearing the initial fMet is positioned in the P site of the ribosome
Chain elongation requires
70s ribosome
mRNA
aminoacyl-tRNAs
elongation factors EF-Tu, EF-Ts, and EF-G
GTP and Mg2+
Function of EF-Tu in translation elongation in E. coli
delivers an aminoacyl-tRNA to the A site of the ribosome
anticodon matches the mRNA codon, EF-Tu hydrolyzes its GTP and dissociates from the ribosome, leaving the aminoacyl-tRNA in the A site
tRNA codon and mRNA codon are mismatched the aminoacyl-tRNA dissociates before EF-Tu hydrolyzes GTP
E. coli ribosomal elongation cycle
delivery of aminoacyl-tRNA
peptidyltransferase
translocation
EF-G-GDP
Translation termination in E. coli
ribosome recycling factor
