Eukaryotic Translation (Protein Synthesis), Animation.

Introduction

This tutorial provides a comprehensive overview of eukaryotic translation, the process by which proteins are synthesized in cells. Understanding translation is crucial for fields such as molecular biology, genetics, and biochemistry. This guide will break down the translation process into clear, actionable steps.

Step 1: Initiation of Translation

Initiation is the first phase of translation, where the ribosome assembles around the mRNA.

1. Formation of the Initiation Complex

   • The small ribosomal subunit binds to the initiator tRNA, which carries the amino acid methionine.
   • This complex attaches to the 5’ cap structure of the mRNA.
   • The ribosome scans along the mRNA to locate the start codon, AUG.

2. Joining of the Large Subunit

   • Once the start codon is found, the large ribosomal subunit joins the complex.
   • All initiation factors are released at this stage.

3. Understanding Ribosomal Sites

   • The ribosome contains three important sites:
     • A-site: Entry site for new tRNA carrying an amino acid.
     • P-site: Holds the tRNA carrying the growing polypeptide chain.
     • E-site: Exit site for tRNA after delivering its amino acid.
   • The initiator tRNA is positioned in the P-site.

Step 2: Elongation of the Polypeptide Chain

In the elongation phase, the polypeptide chain is extended through the addition of amino acids.

1. Entry of Aminoacyl-tRNA

   • A new tRNA carrying an amino acid enters the A-site of the ribosome.
   • The anticodon of the incoming tRNA matches with the mRNA codon in the A-site.

2. Proofreading Process

   • The ribosome checks the match between tRNA anticodon and mRNA codon.
   • Incorrect tRNA with mismatched anticodons is rejected and replaced.

3. Peptide Bond Formation

   • When the correct tRNA enters the A-site, a peptide bond is formed between the amino acids at the P-site and A-site.
   • The tRNA in the P-site releases its amino acids, becoming empty.

4. Translocation of the Ribosome

   • The ribosome moves one codon forward on the mRNA.
   • The empty tRNA moves to the E-site, while the peptidyl tRNA shifts to the P-site.
   • The A-site becomes available for the next tRNA.

5. Repetition of the Cycle

   • This cycle repeats for each codon on the mRNA until a stop codon is reached.

Step 3: Termination of Translation

Termination occurs when a stop codon is encountered in the A-site.

1. Recognition of Stop Codons

   • One of the three stop codons (UAA, UAG, UGA) appears in the A-site.
   • No tRNA can match these codons; instead, they are recognized by a release factor.

2. Cleavage of the Polypeptide

   • The binding of the release factor catalyzes the cleavage of the bond between the polypeptide and the tRNA.
   • The newly synthesized polypeptide is released from the ribosome.

3. Disassembly of the Ribosome

   • The ribosome dissociates into its subunits, preparing for the next round of translation.

4. Post-Translational Modifications

   • The newly formed polypeptide may require further modifications and folding to become an active protein.

Conclusion

This tutorial outlined the process of eukaryotic translation in three main steps: initiation, elongation, and termination. Understanding these steps is fundamental for studying protein synthesis and its implications in biological functions. For further exploration, consider studying post-translational modifications or the role of ribosomal RNA in ribosome structure and function.