mRNA translation is the process by which the genetic code carried by messenger RNA (mRNA) is decoded to produce specific amino acid sequences, or polypeptide chains. It is essentially how cells make proteins.
Key Steps in mRNA Translation:
Here's a breakdown of how mRNA is translated into protein:
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Initiation:
- The process begins with the mRNA molecule binding to a ribosome.
- A special initiator tRNA carrying methionine (Met) binds to the start codon (usually AUG) on the mRNA. This signals the beginning of the protein sequence.
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Elongation:
- The ribosome moves along the mRNA, codon by codon.
- For each codon, a tRNA molecule with the corresponding anticodon brings the correct amino acid to the ribosome.
- The amino acid is added to the growing polypeptide chain through a peptide bond.
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Translocation:
- After a tRNA adds its amino acid, the ribosome shifts down the mRNA by one codon.
- The "empty" tRNA leaves the ribosome and another tRNA carrying the corresponding amino acid will then bind to the next codon, continuing the elongation process.
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Termination:
- The ribosome encounters a stop codon (UAA, UAG, or UGA) on the mRNA.
- Release factors bind to the stop codon, causing the polypeptide chain to be released from the ribosome.
- The ribosome disassociates from the mRNA.
The Role of Ribosomes and Polysomes
The references indicate that mRNAs are usually translated by a series of ribosomes, spaced at intervals of about 100 to 200 nucleotides.
- Ribosomes are the molecular machines that catalyze protein synthesis.
- A polyribosome (or polysome) is a group of ribosomes bound to a single mRNA molecule. Each ribosome within the group functions independently to synthesize a separate polypeptide chain. This allows for the efficient production of multiple copies of the same protein from a single mRNA molecule.
Summary Table
| Step | Description |
|---|---|
| Initiation | mRNA binds to the ribosome, initiator tRNA binds to the start codon. |
| Elongation | The ribosome moves along the mRNA, adding amino acids to the growing polypeptide chain based on the codon sequence. |
| Translocation | After a tRNA adds its amino acid, the ribosome shifts down the mRNA by one codon, making the A site accessible for a new tRNA to bind. |
| Termination | The ribosome encounters a stop codon, releasing the polypeptide chain and disassociating from the mRNA. |
| Polysomes | Multiple ribosomes bind to a single mRNA molecule (at intervals of 100-200 nucleotides), each synthesizing a polypeptide chain independently, increasing efficiency of protein production. |
