Question

Describe the steps in protein synthesis.
Beginning of translation:
Assembly of polypeptide tide:
Completing the polypeptide:

Answer 1

Protein synthesis is the process by which cells generate proteins, and it occurs in two main stages: transcription and translation. Here, we'll focus on the steps of translation, which involves the assembly of amino acids into a polypeptide chain based on the information encoded in mRNA.

### 1. Beginning of Translation
- **Initiation**:
- The small ribosomal subunit binds to the 5' end of the mRNA molecule.
- An initiator tRNA molecule, carrying methionine (the first amino acid), binds to the start codon (AUG) on the mRNA.
- The large ribosomal subunit then joins the complex, forming a complete ribosome with the mRNA and the initiator tRNA at the P site (peptidyl site).

### 2. Assembly of Polypeptide Chain
- **Elongation**:
- The ribosome moves along the mRNA, reading the codons (triplet sequences of nucleotides).
- For each codon, a corresponding tRNA carrying the appropriate amino acid enters the A site (aminoacyl site) of the ribosome.
- A peptide bond is formed between the amino acid in the P site and the amino acid in the A site. This is catalyzed by the ribosomal RNA (rRNA) in the large subunit.
- The tRNA in the P site, now without an amino acid, is released, and the ribosome shifts one codon down the mRNA. The tRNA with the growing polypeptide chain moves from the A site to the P site, and a new tRNA with the next amino acid enters the A site, continuing the process.

### 3. Completing the Polypeptide
- **Termination**:
- The elongation process continues until a stop codon (UAA, UAG, UGA) is encountered in the A site of the ribosome.
- When a stop codon is reached, release factors bind to the ribosome, promoting hydrolysis of the bond between the polypeptide and the tRNA in the P site.
- The newly synthesized polypeptide is released from the ribosome, which then dissociates into its subunits, freeing the mRNA for potential reuse or degradation.

### Summary
In summary, translation begins with the assembly of the ribosome on the mRNA and binding of the initiator tRNA. The polypeptide chain is then elongated by the successive addition of amino acids as the ribosome reads the mRNA codons. Finally, translation terminates upon reaching a stop codon, resulting in the release of the completed polypeptide chain.