Protein- Reynolds Flashcards
Protein synthesis
mRNA is translated into aa sequence
mRNA sequence corresponds to the non-template strand of DNA except
U in place of T in RNA
Codons
- triplet nucleotides bind to anticodon
- 5’ to 3’
- each codon codes for one specific aa
degenerate Codon
Multiple ways to code for the same aa
Start codon
stop codon
- Start codon
- AUG
- corresponds to N-terminus of the protein
- Stop codon
- UAA, UAG, UGA
- corresponds to C-terminus of the protein
Reading Frames
- mRNA= 3 potential reading frames
- DNA= 6 potential reading frames (3 each strand)
Use aa table
first letter vertical
second letter horizontal
third letter find in the box
Splice site mutation
alter the way in which introns are removed
Requirements for protein synthesis
7
- aa
- tRNAs
- aminoacyl-tRNA synthetases
- mRNA
- Ribosomes
- Protein factors
- ATP and GTP
Steps in protein synthesis
5
- Activation of amino acids
- Initiation
- Elongation
- Termination
- Folding and posttranslational processing
tRNA structure
- reads the codons
- stucture
- acceptor stem→ ACC
- anticodon→ tRNA bp w/ codon in mRNA antiparallely
- unique nucleotide bases
Wobble
- allows one anticodon to base pair with several different codons
- If tRNA anticodon recognized only one codon, cells would have a different tRNA for each codon (which they do not)
- First 2 bases of codon form strong H-bonding with anticodon
- Codons that differ in the first two bases require different tRNAs
Ribosome
- mainly rRNA (65%) and some protein
- Different size subunits
- most RNA is rRNA (80%)→ tRNA (15%)→mRNA (5%)
AA activation/tRNA charging
Aminoacyl-tRNA synthetases
- aa activation/charge to cognate tRNA
- specific for one aa and one or more tRNAs
Initiation
SD
Shine-Dalgarno sequence (SD)
- only in prok
- euk has 5’ cap
- purine rich sequence upstream of AUG
Initiation Requires
7
- 30S ribosomal subunit
- 50S ribosomal subunit
- mRNA
- fMet-tRNAfMet
- GTP
- Mg+2
- Initiation factors
Initiation complex
A site = aa attaches
P site=form the peptide bond
E site=Exit
(in euk the introns are gone and the cap is already on)
what recruits the unique fMET-tRNA fMET (Formyl Met)
AUG, start codon
Elongation 3 steps
- Binding of incoming aminoacyl-tRNA
- Peptide bond formation
- Translocation
adding aa to carboxyl end of polypeptide chain N→C direction
Elongation requires
4
- Initiation complex
- Aminoacyl-tRNAs
- Elongation factors
- GTP
Polysomes
In prokaryotes, several ribosomes translating an mRNA simultaneously
coupled transcription/translation
prok. transcription and translation are coupled
euk. mRNAs must leave the nucleus for translation
Termination
- stop codons occupies the A site
- Release factors (RF) hydrolyze the terminal peptidyl bond
- Eelease polypeptide
- dissociation of the ribosome
