tRNA
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Transfer RNA (tRNA) is a crucial component of the protein synthesis machinery in cells. It serves as the adapter molecule that links messenger RNA (mRNA) codons to specific amino acids, facilitating the accurate translation of genetic information into proteins.
Structure of tRNA
Structure of tRNA
1. Cloverleaf Structure:
tRNA molecules typically fold into a distinctive secondary structure known as a cloverleaf structure due to intramolecular base pairing.
The cloverleaf structure consists of four arms:
Acceptor Stem: At one end, the 3' end, where the amino acid attaches.
D Arm: Contains dihydrouridine residues.
TψC Arm: Contains pseudouridine (Ψ) and ribothymidine (T) residues.
Anticodon Arm: At the opposite end from the acceptor stem, it contains the anticodon triplet which base-pairs with the mRNA codon during translation.
2. L-shaped Structure:
The cloverleaf structure folds further into an L-shaped tertiary structure due to additional base pairing and interactions between different parts of the tRNA molecule.
3. Variable Loop (or TΨC Loop):
Contains the TΨC arm and can vary in length and sequence among different tRNA molecules.
Types of tRNA
Types of tRNA
1. Canonical tRNA:
These are the standard tRNA molecules found in cells, each recognizing a specific amino acid and having a distinct anticodon sequence.
2. Non-canonical tRNA:
Some organisms or organelles may have tRNA molecules with unusual features, such as modified bases or altered structures.
Key Points
Key Points
Structure: Cloverleaf and L-shaped structures, with distinct arms and loops.
Types: Canonical and non-canonical tRNAs exist, with canonical tRNAs being the standard in cells.
Activation: Aminoacylation by aminoacyl-tRNA synthetases ensures that each tRNA is correctly charged with its corresponding amino acid before participating in translation.
Understanding the structure, types, and activation process of tRNA is fundamental to comprehending the precise mechanisms involved in protein synthesis and the fidelity of genetic information transfer within cells.
Activation of tRNA
Activation of tRNA
1. Aminoacylation:
Before tRNA can participate in protein synthesis, it must be "charged" with its corresponding amino acid.
Aminoacyl-tRNA synthetases are enzymes responsible for this process, each recognizing a specific tRNA and its corresponding amino acid.
The process involves:
Binding of ATP and the specific amino acid to the synthetase.
Transfer of the amino acid to the 3' end of the tRNA, forming aminoacyl-tRNA.
2. Accuracy Check:
Aminoacyl-tRNA synthetases have proofreading mechanisms to ensure accuracy, preventing incorrect amino acids from being attached to tRNA.
3. Role in Translation:
During translation, aminoacyl-tRNA molecules bring amino acids to the ribosome, where they are incorporated into the growing polypeptide chain according to the mRNA sequence.
The anticodon of the tRNA base-pairs with the complementary mRNA codon, ensuring that the correct amino acid is added to the growing protein.
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