The process of assembling a protein molecule according to the code in an mRNA molecule is called translation. It happens in the cytoplasm of the cell and involves the following key players:
1. mRNA: The messenger RNA molecule carries the genetic code from the DNA in the nucleus to the ribosomes in the cytoplasm.
2. Ribosomes: These are complex molecular machines composed of ribosomal RNA (rRNA) and proteins. They act as the site for protein synthesis, reading the mRNA code and assembling amino acids into a polypeptide chain.
3. tRNA: Transfer RNA molecules are small RNA molecules that act as "adaptors" in the translation process. Each tRNA molecule carries a specific amino acid and recognizes a corresponding codon (three-nucleotide sequence) on the mRNA molecule.
Here's how translation works:
1. Initiation:
- The ribosome binds to the mRNA molecule at a specific start codon (usually AUG).
- The first tRNA molecule carrying the amino acid methionine (Met) binds to the start codon.
2. Elongation:
- The ribosome moves along the mRNA molecule, one codon at a time.
- For each codon, a corresponding tRNA molecule carrying the appropriate amino acid enters the ribosome and binds to the mRNA.
- The ribosome catalyzes the formation of a peptide bond between the amino acid on the incoming tRNA and the growing polypeptide chain.
- The empty tRNA molecule detaches from the ribosome.
3. Termination:
- The process continues until the ribosome encounters a stop codon (UAA, UAG, or UGA) on the mRNA.
- At this point, the ribosome releases the completed polypeptide chain.
In summary:
- The mRNA molecule acts as a blueprint for the protein sequence.
- The ribosome reads the mRNA code and assembles amino acids into a polypeptide chain.
- tRNA molecules act as adaptors, bringing the correct amino acids to the ribosome based on the mRNA code.
- The process is initiated at a start codon and terminates at a stop codon.
Outcome:
The final polypeptide chain folds into a specific three-dimensional structure, forming a functional protein. The structure of the protein dictates its function, which can be anything from catalyzing biochemical reactions to transporting molecules across cell membranes.
Note:
This is a simplified overview of the process. There are many other factors involved in translation, such as initiation factors, elongation factors, and release factors. Additionally, post-translational modifications can further modify the protein structure and function.
