M03.04.03 Amino Acid Activation and Codon Translation by tRNAs

Amino acids are essential building blocks of proteins, but they lack a direct affinity for mRNA. To facilitate translation, an adapter molecule called transfer RNA (tRNA) is required. This document discusses the processes of amino acid activation and codon translation by tRNAs.

Amino Acid Activation

Amino acid activation is the process by which tRNAs combine with their corresponding amino acids in the cytoplasm. This process is crucial for ensuring that the correct amino acid is added during protein synthesis.

Process Overview

1. Entry of tRNA: Each tRNA enters the cytoplasm.
2. Cognate Amino Acid Binding: Each tRNA binds to its specific amino acid in a reaction facilitated by aminoacyl-tRNA synthetase.
3. Energy Requirement: Two high-energy bonds from ATP are utilized in the activation process.

Activation Steps

Important Features

• Aminoacyl-tRNA Synthetases: Each amino acid is activated by a specific aminoacyl-tRNA synthetase, ensuring accuracy in pairing.
• Self-Checking Mechanism: These synthetases possess self-checking functions to prevent the formation of incorrectly paired aminoacyl-tRNAs. However, if an error occurs (e.g., ala-tRNA^ser), there is no mechanism during translation to detect it, which may result in an incorrect amino acid being incorporated into a protein.

Codon Translation by tRNAs

Each tRNA has an anticodon sequence that pairs with the codon for its cognate amino acid in the mRNA. This interaction is crucial for accurate translation.

Anticodon-Codon Interaction

• Complementary and Antiparallel Orientation: The base pairing between the tRNA anticodon and the mRNA codon follows complementary and antiparallel rules.
• Example: The aminoacyl-tRNA for arginine (arg-tRNA^arg) has the anticodon sequence UCG, allowing it to pair with the arginine codon CGA in mRNA.

Diagram of Amino Acid Activation

Points to Remember

• tRNA acts as an adapter between amino acids and mRNA.
• Amino acid activation involves specific aminoacyl-tRNA synthetases.
• Energy from ATP is required for the activation process.
• Accurate pairing of tRNA and amino acids is crucial for proper protein synthesis.

Bibliography

1. Berg, J. M., Tymoczko, J. L., & Stryer, L. (2015). Biochemistry. W.H. Freeman and Company.
2. Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., & Walter, P. (2014). Molecular Biology of the Cell. Garland Science.
3. Lodish, H., Berk, A., Kaiser, C. A., Krieger, M., Scott, M. P., & Bretscher, A. (2016). Molecular Cell Biology. W.H. Freeman and Company.