Why would cells die if they were unable to make (or otherwise obtain) the amino acid arginine?

Arginine is an amino acid that is incorporated into proteins. So if cells can not make or obtain arginine, the cell can not make proteins needed for survival.

Explanation:

Arginine is an amino acid used to build proteins, and it is classified as a semiessential or conditionally essential amino acid.

Proteins are large molecules consisting of long chains of amino acids. They perform many functions such as catalysing metabolic reactions, providing structure to cells and organisms, and transporting molecules, among many others.

Most notably, arginine is part of proteins that play an important role in many different processes such as cell division, immune function, wound healing and the release of hormones. Without this amino acid, the cell cannot manufacture the proteins necessary for proper functioning. So the cell dies because it cannot function properly.