1. mRNA carries the blueprint:
* The DNA sequence that codes for a specific protein is transcribed into mRNA. This mRNA molecule carries the genetic information from the nucleus to the ribosome in the cytoplasm.
* mRNA consists of codons, each three-nucleotide sequence that codes for a specific amino acid.
2. Ribosome binds to mRNA:
* The ribosome has two subunits: the small subunit and the large subunit.
* The small subunit binds to the mRNA molecule, recognizing a special start codon (AUG) that signals the beginning of the protein-coding sequence.
3. tRNA delivers amino acids:
* Transfer RNA (tRNA) molecules are responsible for carrying specific amino acids to the ribosome.
* Each tRNA molecule has an anticodon that recognizes and binds to a complementary codon on the mRNA.
* The tRNA carrying the first amino acid (determined by the start codon AUG) binds to the ribosome.
4. Peptide bond formation:
* The ribosome moves along the mRNA, reading each codon sequentially.
* As it reads each codon, the corresponding tRNA brings in the correct amino acid.
* The large subunit of the ribosome catalyzes the formation of a peptide bond between the amino acids, linking them together to form a growing polypeptide chain.
5. Elongation and termination:
* The ribosome continues moving along the mRNA, adding more amino acids to the polypeptide chain.
* This process of elongation continues until the ribosome encounters a stop codon (UAA, UAG, or UGA) on the mRNA.
* Stop codons signal the end of the protein sequence.
6. Protein release and folding:
* Once the stop codon is reached, the ribosome releases the completed polypeptide chain.
* The polypeptide chain then folds into its three-dimensional structure, guided by interactions between its amino acids.
In summary, the ribosome "knows" which protein to make because it reads the genetic code in mRNA, which is a copy of the DNA sequence that codes for that protein. The ribosome uses this information to assemble amino acids into a polypeptide chain in the order specified by the codons on the mRNA. This polypeptide chain then folds into the final three-dimensional structure of the protein.
