Translation In Eukaryotes II Protein Synthesis

 The translation is the process of synthesizing proteins from the information encoded in mRNA. In eukaryotic cells, this process occurs in the cytoplasm and involves a complex machinery consisting of ribosomes, tRNAs, and numerous translation factors. The process of translation in eukaryotes can be divided into three main stages: initiation, elongation, and termination. Each stage involves a specific set of proteins and processes that work together to ensure accurate and efficient protein synthesis.

Initiation: 

The initiation of translation in eukaryotes is a complex process that involves several steps.

·         The first step is the binding of the small ribosomal subunit to the 5' end of the mRNA. This binding is facilitated by a protein called the cap-binding complex (CBC), which recognizes the 5' cap structure of the mRNA. Once the small ribosomal subunit is bound, it scans along the mRNA in a 5' to 3' direction until it encounters the first AUG codon, which serves as the start codon for protein synthesis.

·         The next step in initiation involves the recruitment of translation initiation factors (eIFs), which help to stabilize the complex and promote the correct positioning of the mRNA on the ribosome. The eIFs also help to recruit the initiator tRNA (tRNAiMet), which carries the first amino acid (methionine) of the protein. The initiator tRNA is bound to the eIF2 complex, which is a GTP-binding protein that helps to ensure that the correct tRNA is selected.

·         The final step in initiation involves the binding of the large ribosomal subunit, which completes the formation of the functional ribosome. This binding is facilitated by eIF5, which helps to stabilize the interaction between the small and large ribosomal subunits.

Elongation:

 Once initiation is complete, the ribosome is ready to begin the elongation phase of translation. During elongation, the ribosome moves along the mRNA in a 5' to 3' direction, reading each codon and bringing in the appropriate aminoacyl-tRNA to add to the growing polypeptide chain. The incoming aminoacyl-tRNA is brought to the ribosome by another set of protein factors called elongation factors (eEFs).

The process of elongation involves three main steps:

• ·       Codon recognition,
• ·         Peptide bond formation,
• ·         Translocation.

In the first step, the incoming aminoacyl-tRNA binds to the codon in the mRNA, a process that is facilitated by the eEF1 complex.

 In the second step, the amino acid on the incoming tRNA is covalently bonded to the growing polypeptide chain, a process catalyzed by the peptidyl transferase activity of the ribosome.

 In the final step, the ribosome moves along the mRNA by one codon, a process called translocation, which is facilitated by the eEF2 complex.

Termination:

 The final stage of translation is termination, which occurs when the ribosome encounters a stop codon in the mRNA. There are three stop codons (UAA, UAG, and UGA) that signal the end of protein synthesis. When a stop codon is encountered, a release factor (eRF) binds to the A site of the ribosome, causing the polypeptide chain to be released from the ribosome. The ribosome then dissociates into its component subunits, ready to initiate translation on a new mRNA.

In summary, the process of translation in eukaryotes is a complex and highly regulated process that involves numerous protein factors and occurs in three main stages: initiation, elongation, and termination.