31 Questions
What is the primary reason for the high conservation of aminoacyl-tRNA synthetases across species?
To ensure the correct amino acid attachment to tRNA
What is the main purpose of the pre-transfer editing mechanism in aminoacyl-tRNA synthetases?
To hydrolyze incorrectly charged tRNA molecules
What is the intermediate formed during the amino acid activation reaction catalyzed by aminoacyl-tRNA synthetases?
Aminoacyl-adenylate
What is the primary region of the tRNA molecule recognized by aminoacyl-tRNA synthetases?
Acceptor stem
What is the consequence of defective editing mechanisms in aminoacyl-tRNA synthetases?
Increased error frequency in protein sequences
What is the primary function of the peripheral domains of aminoacyl-tRNA synthetases?
To provide additional functional diversity
What is the energy source that drives the amino acid activation reaction?
Energy from the destruction of PPi
What is the function of the enzyme Met-tRNA transformilase?
To introduce the formyl group into the tRNA
What is the difference between Class I and Class II aminoacyl-tRNA synthetases?
Class I synthetases transfer the amino acid to the 2'OH of the tRNA, while Class II synthetases transfer to the 3'OH
What is the amino acid that is modified to become selenocysteine?
Serine
What is the region of the tRNA molecule recognized by aminoacyl-tRNA synthetases?
The acceptor stem
What is the consequence of the amino acid activation reaction?
The formation of an aminoacyl-AMP complex
What is the characteristic of the amino acid selenocysteine?
It is synthesized from serine
What is the structure of Class I aminoacyl-tRNA synthetases?
Monomeric
What is the purpose of the union of the amino acid to the tRNA?
To facilitate the formation of the peptide bond
What is the result of the breakdown of the pyrophosphate in the amino acid activation reaction?
Formation of 2 monophosphates
What is the location of the aminoacyl-tRNA synthetases in eukaryotes?
Both in the cytoplasm and mitochondria
What is the role of the aminoacyl-tRNA synthetases in protein synthesis?
To form a covalent bond between the amino acid and the tRNA
What is the purpose of the ATP in the amino acid activation reaction?
To activate the amino acid by forming a 5'-aminoacyl adenylate
How many different aminoacyl-tRNA synthetases can form a complex in the cytoplasm?
Up to 11
What codifies the mitochondrial aminoacyl-tRNA synthetases?
Nuclear genes
What is the outcome of the attack of the carboxyl group of the amino acid on the ATP?
Formation of a 5'-aminoacyl adenylate
In some bacteria and archaea, which amino acid is charged onto tRNA?
Glutamate
What is the role of the protein that recognizes the tRNA of selenocysteine and attracts it to the ribosome?
Factor of elongation
What is the codon recognized by the termination factor?
UGA
Which amino acid is not ancestral, but is coded by a codon that was previously used by another amino acid?
Glutamine
In eukaryotes, what is the state of glutamine?
Free
What is the role of the aminotransferase in glutamine synthesis?
Transforms glutamate into glutamine
Which protein participates in antioxidant reactions and contains selenocysteine?
Glutathione peroxidase
What is the intermediate in the reaction catalyzed by selenocysteine synthase?
Seril-tRNASec
Which amino acid has its own enzyme that charges it onto its specific tRNA?
Pirrolisine
Study Notes
Aminoacyl-tRNA Synthetases
Evolutionary Conservation
- Aminoacyl-tRNA synthetases are highly conserved across species, indicating their essential role in translation.
- The core catalytic domain is highly conserved, while the peripheral domains show more variation.
- Conservation of amino acid sequences and structures across species highlights their importance in maintaining protein synthesis fidelity.
Editing Mechanisms
- Aminoacyl-tRNA synthetases have built-in editing mechanisms to ensure correct amino acid attachment to tRNA.
- Editing mechanisms include:
- Pre-transfer editing: hydrolysis of incorrectly charged tRNA molecules.
- Post-transfer editing: proofreading and correction of mischarged tRNA molecules.
- Editing mechanisms help maintain the fidelity of protein synthesis by reducing errors.
Amino Acid Activation
- Aminoacyl-tRNA synthetases catalyze the reaction between amino acids and tRNA molecules.
- The reaction involves the formation of an aminoacyl-adenylate intermediate, which is then transferred to the tRNA molecule.
- Amino acid activation is a two-step process:
- Amino acid is adenylated, forming an aminoacyl-adenylate intermediate.
- The intermediate is then transferred to the tRNA molecule, forming an aminoacyl-tRNA molecule.
tRNA Recognition
- Aminoacyl-tRNA synthetases recognize specific tRNA molecules through interactions with the tRNA acceptor stem and anticodon.
- Recognition is based on the sequence and structure of the tRNA molecule, ensuring correct pairing with the corresponding amino acid.
- tRNA recognition is crucial for maintaining the fidelity of protein synthesis.
Error Correction
- Aminoacyl-tRNA synthetases have error correction mechanisms to prevent incorrect amino acid incorporation.
- Errors can occur due to:
- Misactivated amino acids.
- Incorrect tRNA recognition.
- Error correction mechanisms include:
- Hydrolysis of incorrectly charged tRNA molecules.
- Proofreading and correction of mischarged tRNA molecules.
- Error correction mechanisms help maintain the fidelity of protein synthesis.
Learn about the crucial role of aminoacyl-tRNA synthetases in protein synthesis, including their evolutionary conservation, editing mechanisms, amino acid activation, tRNA recognition, and error correction mechanisms. Understand how these enzymes ensure the fidelity of protein synthesis.
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