Final answer:
The principal carrier protein in vertebrate blood is albumin, which serves as a generalized carrier for various substances, including steroids, playing a significant role in cellular transport and regulatory functions.
Step-by-step explanation:
The principal carrier protein in vertebrate blood that binds non-specifically to various substances, including some steroids, is albumin.
Carrier proteins are crucial for the transport of substances across cell membranes. Specific carrier proteins are typically dedicated to transporting certain molecules like glucose or amino acids due to their selective nature. In contrast, albumin acts as a generalized carrier that can bind various substances including fatty acids, steroid hormones, and other compounds. Its ability to transport different substances makes it essential in maintaining osmotic pressure and the distribution of various molecules throughout the body.
Steroid hormones, for example, rely on carrier proteins like albumin for transport in the bloodstream before they can diffuse through the lipid bilayer of target cells and adhere to intracellular receptors, regulating gene expression and influencing cellular functions.