[W1] Eukaryote translation Flashcards
(34 cards)
What is translation?
The synthesis of proteins from an mRNA template by the ribosome
What is required for translation?
- mRNA
- Ribosome
- tRNA
- Initiation, elongation, and release factors
- Energy (ATP and GTP)
What are the three stages of translation?
- Initiation
- Elongation
- Termination
What are the ribosomal subunits in eukaryotes?
40S (small) and 60S (large), together forming the 80S ribosome
What are the three tRNA binding sites in the ribosome?
- A site (aminoacyl site)
- P site (peptidyl site)
- E site (exit site)
What happens at each ribosomal site?
- A: tRNA enters with amino acid
- P: tRNA holds growing peptide
- E: tRNA exits after peptide transfer
What is a codon?
A sequence of three mRNA bases that codes for an amino acid or stop signal
How many codons are there?
64 total codons — 61 for amino acids, 3 stop codons (UAA, UAG, UGA)
What is the wobble hypothesis?
Flexibility in base pairing at the third codon position allows some tRNAs to bind multiple codons
What is aminoacyl-tRNA?
A tRNA molecule bound to its corresponding amino acid
What enzyme charges tRNA with amino acids?
Aminoacyl-tRNA synthetase, using ATP in a two-step reaction
What is the start codon for translation?
AUG, which codes for methionine (Met)
What is the initiator tRNA in eukaryotes?
Met-tRNAi — specialized for initiation and not formylated like in prokaryotes
What is the 43S pre-initiation complex?
Contains 40S subunit, Met-tRNAi, and initiation factors (eIF2, eIF3, eIF1, eIF1A)
What is the role of the cap-binding complex?
Binds the 5′ cap of mRNA using eIF4E, eIF4G, and PABP, facilitating ribosome binding
What happens during scanning?
The 43S complex scans mRNA from 5′ to 3′ for the AUG start codon
What is the 48S initiation complex?
Formed when Met-tRNAi base-pairs with the AUG start codon
What is the final step of initiation?
GTP hydrolysis by eIF5 and eIF5B leads to 60S subunit joining and formation of 80S ribosome
How is translation initiation regulated?
- eIF4E availability and phosphorylation
- eIF2B phosphorylation (inhibitory)
What is an IRES?
A sequence allowing ribosome binding internally on mRNA, bypassing the 5′ cap
What occurs during elongation?
- Aminoacyl-tRNA enters A site (eEF1A-GTP)
- Peptide bond forms (peptidyl transferase on 60S)
- Ribosome translocates (eEF2-GTP)
- Deacylated tRNA exits via E site
What does eEF1A do?
Binds aminoacyl-tRNA and GTP, delivers it to the A site
What does eEF1B/1γ do?
Acts as GEF to recycle eEF1A by replacing GDP with GTP
What does eEF2 do?
Translocates the ribosome along the mRNA using GTP
