What are the roles of the small and large ribosomal subunits?

The small ribosomal subunit reads the RNA, while the large subunit joins amino acids to form a polypeptide chain.

Ribosomes, the protein factories of the cell, are composed of two subunits: a small one and a large one. Each of these subunits plays a crucial role in protein synthesis, the process by which the genetic code is translated into proteins.

The small ribosomal subunit is responsible for reading the messenger RNA (mRNA). It binds to the mRNA molecule and moves along it, reading the genetic code in the form of codons, which are sequences of three nucleotides. Each codon corresponds to a specific amino acid or a stop signal. The small subunit ensures that the mRNA is in the correct position for the translation process to occur.

The large ribosomal subunit, on the other hand, is where the actual process of protein synthesis takes place. It contains a peptidyl transferase centre, which is responsible for forming the peptide bonds between amino acids. Transfer RNA (tRNA) molecules bring the appropriate amino acids to the ribosome, according to the codon being read by the small subunit. The large subunit then catalyses the reaction that joins these amino acids together, forming a polypeptide chain. This chain will eventually fold into a functional protein.

In summary, the small and large ribosomal subunits work together to translate the genetic code into proteins. The small subunit reads the mRNA, while the large subunit joins the amino acids together. This process is fundamental to the functioning of all living cells, as proteins are involved in virtually all cellular processes.