A site

Definition

The A site, also known as the aminoacyl site, is a specific location on the ribosome where the incoming aminoacyl-tRNA (charged tRNA) binds during the process of protein synthesis, or translation. The A site is one of the three tRNA binding sites on the ribosome, along with the P site and the E site.

5 Must Know Facts For Your Next Test

1. The A site is where the incoming aminoacyl-tRNA binds to the ribosome during the elongation stage of protein synthesis.
2. The A site ensures the correct amino acid is added to the growing polypeptide chain by checking the anticodon of the incoming aminoacyl-tRNA against the codon on the mRNA.
3. The binding of the aminoacyl-tRNA to the A site triggers the formation of a new peptide bond between the amino acid in the A site and the amino acid in the P site.
4. After the peptide bond is formed, the ribosome translocates, moving the tRNA in the A site to the P site and the tRNA in the P site to the E site.
5. The A site is essential for maintaining the reading frame and ensuring the accurate synthesis of the correct protein.

Review Questions

• Explain the role of the A site in the process of protein synthesis.
  • The A site on the ribosome is where the incoming aminoacyl-tRNA, carrying the next amino acid to be added to the growing polypeptide chain, binds during the elongation stage of translation. The A site ensures the correct amino acid is added by checking the anticodon of the aminoacyl-tRNA against the codon on the mRNA. Once the correct aminoacyl-tRNA is bound, the A site triggers the formation of a new peptide bond, connecting the amino acid in the A site to the amino acid in the P site. This process is essential for maintaining the reading frame and synthesizing the correct protein.
• Describe the relationship between the A site, P site, and E site on the ribosome during protein synthesis.
  • The A site, P site, and E site on the ribosome work together to facilitate the step-by-step process of protein synthesis. The A site is where the incoming aminoacyl-tRNA binds and the new peptide bond is formed. The P site holds the tRNA carrying the growing polypeptide chain. The E site is where the deacylated tRNA exits the ribosome after its amino acid has been transferred. As the ribosome translocates, the tRNA in the A site moves to the P site, the tRNA in the P site moves to the E site, and a new aminoacyl-tRNA enters the A site. This coordinated movement of the tRNAs through the three binding sites on the ribosome is essential for the accurate and efficient synthesis of proteins.
• Analyze the importance of the A site in ensuring the fidelity of protein synthesis.
  • The A site plays a critical role in maintaining the fidelity of protein synthesis by verifying the accuracy of the incoming aminoacyl-tRNA. The A site checks the anticodon of the aminoacyl-tRNA against the codon on the mRNA to ensure the correct amino acid is being added to the growing polypeptide chain. If the wrong aminoacyl-tRNA binds to the A site, it will not form a proper codon-anticodon interaction, and the ribosome will reject it. This proofreading function of the A site is essential for preventing the incorporation of incorrect amino acids, which could lead to the production of non-functional or potentially harmful proteins. By ensuring the accuracy of each step in translation, the A site contributes to the overall fidelity and integrity of the final protein product.

Related terms

P site: The P site, or peptidyl site, is the location on the ribosome where the tRNA carrying the growing polypeptide chain is bound during protein synthesis.

E site: The E site, or exit site, is the location on the ribosome where the deacylated tRNA (tRNA without an amino acid) exits the ribosome after its amino acid has been transferred to the growing polypeptide chain.

Aminoacyl-tRNA: Aminoacyl-tRNA is a tRNA molecule that has been charged with an amino acid, ready to be incorporated into the growing polypeptide chain during translation.