Lecture 5 - Translation Flashcards
What does Degenerate code mean
Multiple codons encode for the same amino acid
What is the only start codon in Eukaryotes
Methionine AUG
What do prokaryotes also use as start codons alongside methionine
GUG and UUG
What are the 3 kinds of RNA
mRNA,
rRNA,
tRNA
How is Ribosomal RNA processed
Synthesised by pol I
Not translated into protein
Processed by cleavage and chemical modifications into final form
Packaged with proteins in the nucleolus
What is snoRNAs
Small nucleolar RNA
60-300 nucleotides
Involved in processing rRNA
Many come from introns of protein-coding genes
What is tRNA
RNA with complex secondary structure
Transcribed by RNA pol III
Anticodons bind to mRNA codons
Charged with 1 AA each
What is aminoacylation
Aminoacylation is a two-step process in which amino acids are first activated by ATP, forming an intermediate aminoacyl adenylate, and then transferred to the 3′-end of tRNA to form the aminoacyl-tRNA end-product by ARS (Aminoacyl-tRNA synthetases)
What is the translation pre-initiation complex
Met-tRNA binds small ribosomal subunit
With eIF2 (eukaryotic initiation factor 2) + GTP
40S complex (S = sedimentation coefficient)
Describe the process for mRNA binding to 40S complex
eIF4 proteins binds the mRNA cap
mRNA folded on itself through interaction between polyA tail binding protein and eIF4 complex
eIF4 complex binds to eIF2 in the 40S subunit
43S complex
How is the large ribosomal subunit recruited
ATP hydrolysis powers scanning
GTP hydrolysis leads to release of eIF proteins and binding of Met-tRNA to large subunit
Met-tRNA is in the middle of three tRNA binding pockets
What are the Large ribosomal subunit tRNA binding sites
A site - Aminoacyl-tRNA
P site - Peptidyl-tRNA
E site - empty or exit
What is EF1(alpha)
aa-tRNA binds its codon to A site, then EF1alpha
Elongation factor 1 alpha is powered by GTP hydrolysis
How does conformational change occur in translation
GTP hydrolysis brings amino acids together
Describe transpeptidation
Ribozyme catalyses formation of the peptide bond between two amino acids
Peptidyl transferase transfers the peptide onto the growing chain
Amino acid dissociates from tRNA in the P site
Describe translocation in translation
tRNA with polypeptide chain moves into P site
Empty tRNA moves into the E site and is released
Powered by GTP hydrolysis - breaking the bond between 2nd and 3rd phosphate group of GTP –> GDP
Describe how termination occur
Release factor protein complex binds a STOP codon (eRF1 subunit)
No more peptide bonds can be formed
GTP hydrolysis (eRF3 subunit) –> complex falls apart, releasing the new polypeptide
What is wobble base-pairing
Base pairing is loose in the third position of tRNA-mRNA interaction
Accounts for redundancy in last letter of codons in genetic code on 5’ wobble position on tRNA (3’ mRNA)
What is a neutral or silent mutation
does not affect protein sequence
What is a neutral amino acid substitution
change does not affect protein function
What is a Ribonucleoprotein
RNA + protein complexes
What is a brief summary of translation
tRNAs are ‘charged’ with one amino acid each
tRNA anticodon bind mRNA codon
Met-tRNA is initiator
Translation PIC = Met-tRNA, eIF2, GTP, small ribosomal subunit
eIF4 complex brings mRNA to PIC
Large ribosomal subunit arrives last
Conformational changes driven by energy from GTP hydrolysis moves tRNA through A, P, and E sites
rRNA ribozyme catalyses peptide bonds in ribosome
eRF1 binds STOP codon, terminates polypeptide chain
Polyribosomes in the cytosol or tethered to ER
