Protein synthesis does not occur in the nucleus. Instead, it takes place in the cytoplasm of the cell, specifically on ribosomes. Here’s a brief explanation of the process:
1. Transcription: The first step of protein synthesis is transcription, which occurs in the nucleus. During transcription, the DNA sequence of a gene is copied into messenger RNA (mRNA). This mRNA carries the genetic information from the DNA to the ribosomes.
2. mRNA Processing: After transcription, the mRNA undergoes processing, including the addition of a 5′ cap and a poly-A tail, as well as the removal of introns (non-coding regions). This processed mRNA then exits the nucleus through nuclear pores.
3. Translation: Once the mRNA reaches the cytoplasm, it binds to a ribosome. The ribosome reads the mRNA sequence and translates it into a sequence of amino acids, forming a polypeptide chain. This process is called translation.
4. Protein Folding and Modification: After translation, the polypeptide chain folds into its functional three-dimensional structure, becoming a protein. The protein may also undergo additional modifications, such as the addition of chemical groups, to become fully functional.
In summary, while the initial step of protein synthesis (transcription) occurs in the nucleus, the actual synthesis of proteins (translation) happens in the cytoplasm on ribosomes.