Protein synthesis, the creation of proteins from amino acids, is a fundamental process in all living organisms. It's a two-step process involving transcription and translation.
Transcription: From DNA to mRNA
- Initiation: RNA polymerase, an enzyme, binds to a specific region of DNA called the promoter, initiating the process.
- Elongation: RNA polymerase moves along the DNA template, unwinding the double helix and synthesizing a complementary mRNA (messenger RNA) molecule. This mRNA molecule carries the genetic code from the DNA. Each three-nucleotide sequence on the mRNA, called a codon, specifies a particular amino acid.
- Termination: RNA polymerase reaches a termination sequence on the DNA, signaling the end of transcription. The newly synthesized mRNA molecule is released.
Translation: From mRNA to Protein
Translation occurs in the cytoplasm on ribosomes, which are cellular structures responsible for protein synthesis.
- Initiation: The ribosome binds to the mRNA molecule and identifies the start codon (AUG). A special tRNA (transfer RNA) molecule, carrying the amino acid methionine, binds to the start codon.
- Elongation: tRNA molecules, each carrying a specific amino acid, enter the ribosome. The anticodon on the tRNA (a three-nucleotide sequence) base-pairs with the complementary codon on the mRNA. A peptide bond forms between the adjacent amino acids, lengthening the polypeptide chain. This process continues as the ribosome moves along the mRNA, reading codon after codon.
- Termination: When a stop codon (UAA, UAG, or UGA) is encountered, the ribosome releases the completed polypeptide chain. The polypeptide chain then folds into a three-dimensional structure, becoming a functional protein.
The accuracy of protein synthesis relies on precise base pairing between codons and anticodons, ensuring the correct amino acids are incorporated into the growing polypeptide chain. The formation of aminoacyl-tRNA is a crucial step in maintaining this accuracy. [See reference: Domain-specific recruitment of amide amino acids for protein synthesis]
