Ribosome-nascent chain complex

Ribosome-nascent chain complex

The ribosome-nascent chain complex (RNC) is a molecular structure formed during the process of protein synthesis in cells. It consists of a ribosome bound to a nascent polypeptide chain that is being synthesized. The RNC plays a crucial role in the translation phase of gene expression, where the genetic code carried by messenger RNA (mRNA) is decoded to produce a specific polypeptide.

Structure

The ribosome is a large ribonucleoprotein complex composed of two subunits: the small ribosomal subunit and the large ribosomal subunit. The nascent chain is the emerging polypeptide that is synthesized by the ribosome as it reads the mRNA sequence. The RNC is stabilized by interactions between the ribosome and the nascent chain, as well as by various chaperone proteins that assist in the proper folding of the nascent polypeptide.

Function

The primary function of the RNC is to facilitate the synthesis of proteins by translating the genetic information encoded in mRNA. During translation, the ribosome moves along the mRNA, decoding its sequence into a corresponding sequence of amino acids. The nascent chain grows as amino acids are added one by one, forming a polypeptide that will eventually fold into a functional protein.

Translation Process

The translation process can be divided into three main stages:

• Initiation: The small ribosomal subunit binds to the mRNA and the initiator transfer RNA (tRNA) carrying the first amino acid, usually methionine. The large ribosomal subunit then joins to form the complete ribosome.
• Elongation: The ribosome moves along the mRNA, and tRNAs bring amino acids to the ribosome, where they are added to the growing nascent chain.
• Termination: When the ribosome encounters a stop codon on the mRNA, translation ends, and the nascent chain is released from the ribosome.

Role of Chaperones

Chaperone proteins play a vital role in the RNC by assisting in the proper folding of the nascent polypeptide. These chaperones prevent misfolding and aggregation of the nascent chain, ensuring that it attains its correct three-dimensional structure. Some well-known chaperones involved in this process include the Hsp70 and Hsp90 families.

Clinical Significance

Defects in the translation process or in the function of the RNC can lead to various diseases, including neurodegenerative disorders and cancer. Understanding the mechanisms of the RNC and its associated chaperones is crucial for developing therapeutic strategies for these conditions.

See Also

• Ribosome
• Translation (biology)
• Messenger RNA
• Transfer RNA
• Chaperone (protein)