L9 Translation Flashcards
What are ribosomes?
Ribosomes are large, abundant RNP particles, consisting of two unequal subunits.
Ribosome consists of two RNP subunits, what are they and what are their functions?
Small subunit: responsible for decoding the mRNA sequence.
Large subunit: responsible for forming peptide bonds between amino acids.
Explain ribosome synthesis in eukaryotes.
Ribosome synthesis is a complex and energy-intensive process. It involves:
- Transcription and early processing of rRNA: Occurs in the nucleolus
- Later processing and assembly: Occurs in the nucleoplasm and cytoplasm
- Export from the nucleus: Functionally active ribosomes are generated after export
What is the function of ribosomes?
Ribosomes are the cellular machinery responsible for protein synthesis. They translate the genetic information encoded in mRNA into amino acid sequences, which are then assembled into proteins.
How many tRNAs are bound to the ribosome during translation elongation?
Two tRNAs are bound to the ribosome at any given time during translation elongation.
What are the three steps of translation elongation?
- Aminoacyl-tRNA binding
- Peptide bond formation
- Translocation of the ribosome along the mRNA
What factor delivers aminoacyl-tRNA to the ribosome?
Elongation factor EF1A (EF-Tu in prokaryotes)
What factor is required for translocation?
Elongation factor EF2 (EF-G in prokaryotes)
What is the energy source for translation elongation?
Hydrolysis of GTP molecules. Two GTP molecules are hydrolyzed per elongation cycle.
How are initiator methionyl-tRNAs different from elongator methionyl-tRNAs?
Initiator methionyl-tRNAs are distinct from elongator methionyl-tRNAs and bind to the start codon (AUG) in association with eukaryotic initiation factor 2 (eIF2, IF2 in prokaryotes).
What is the role of eIF2?
eIF2 is a GTPase that facilitates the binding of initiator methionyl-tRNA to the start codon.
What selects the initiation codon in prokaryotic cells?
16S/mRNA base pairing
How is the start codon positioned in the P site?
The Shine-Dalgarno (SD) sequence within prokaryotic mRNAs is recognized by base-pairing with nucleotides at the 3’ end of the 16S rRNA.
How does the initiation complex assemble at the 5’ end of mRNA in eukaryotes?
The initiator tRNA (bound to eIF2), together with the small ribosomal subunit, is assembled at the 5’ end of the mRNA through interaction with the cap-binding complex (CBC).
What is the role of the Kozak sequence in translation initiation?
The pre-initiation complex scans along the mRNA, using the helicase activity of CBC, until it finds an AUG codon within an appropriate sequence context: the Kozak sequence.
