WJEC Biology Practice Exam

Protein synthesis primarily occurs at ribosomes, which are the essential machinery of the cell responsible for translating mRNA into polypeptide chains, forming proteins. Ribosomes can be found floating freely in the cytoplasm or attached to the endoplasmic reticulum, creating rough ER. The process begins when messenger RNA (mRNA) is produced in the nucleus and then transported to the ribosomes in the cytoplasm. Here, ribosomes read the sequence of codons in the mRNA and facilitate the assembly of amino acids into a specific protein according to the genetic code.

The ribosome plays a crucial role because it has two subunits that come together during protein synthesis, and it has binding sites for both mRNA and the transfer RNA (tRNA) that carries amino acids. This functional aspect of ribosomes is what makes them the central site for protein synthesis in the cell.