Final answer:
Fibrin is the protein that forms insoluble strands and is responsible for the formation of blood clots through the coagulation process, where soluble fibrinogen is converted by the enzyme thrombin.
Step-by-step explanation:
The protein that forms insoluble strands and makes up blood clots is known as fibrin. During the coagulation process, fibrinogen, which is a soluble protein produced by the liver, is converted into fibrin. This conversion is mediated by the enzyme thrombin, which is activated from its inactive form, prothrombin, through a series of reactions known as the clotting cascade.
Fibrin then forms a mesh-like structure that traps platelets and red blood cells, solidifying into a clot that seals the damaged blood vessel. This process is essential to prevent excessive blood loss following injury.