Question

The term subunit can be used in a variety of ways. What is the difference between a protein subunit and a ribosomal subunit?

Short answer

A protein subunit refers to an individual polypeptide within a larger protein that either functions independently or forms a functional protein complex and a ribosomal subunit refers to one of the two parts of a ribosome (large and small) that facilitate protein synthesis.

Step-by-step solution

Defining Protein Subunit

A protein subunit is an individual polypeptide within a larger protein complex. These proteins can function individually or they can combine (typically through non-covalent interactions) to form a larger, functional protein complex.

Defining Ribosomal Subunit

In the context of a ribosome, a subunit refers to the two distinct parts of the ribosome that come together to facilitate protein synthesis. Ribosomes are composed of two subunits: a large subunit and a small subunit. Each of these has a distinct role in protein synthesis.

Comparing the Two

Protein and ribosomal subunits, while both being subunits, have distinct roles and structures. Protein subunits refer to individual polypeptide chains in a protein complex, while ribosomal subunits refer to independent structural entities in a ribosome which have specific roles in protein synthesis. Essentially, protein subunits aid in the structure and functionality of proteins, whilst ribosomal subunits have a more directed role in the formation of new proteins via translation.