Final answer:
Chemical messengers like hormones and neurotransmitters often require a carrier protein to move through the bloodstream, as many are insoluble or hydrophobic, necessitating the use of these specialized proteins for transport to target cells.
Step-by-step explanation:
Chemical messengers that may require a carrier protein to move through the bloodstream include hormones, neurotransmitters, and certain drugs. These molecules are often not soluble in water on their own and may be too large or too hydrophobic to move freely in the aqueous environment of the bloodstream. For example, steroid hormones and thyroid hormones are hydrophobic and must bind to carrier proteins to become soluble and be transported to their target cells. Similarly, insulin influences the number of glucose transport proteins (GLUTs) on cells to facilitate the uptake of glucose from the blood, an important process that is altered in diabetic patients.
Carrier proteins operate by binding to the molecule they transport, which triggers a conformational change in the protein, allowing the molecule to move across the cell membrane. This process is different from how channel proteins operate, as carrier proteins transport molecules at a much slower rate. Some proteins, also known as integral proteins, facilitate the passage of certain molecules through the cell membrane, indicating the specificity and importance of carrier protein-mediated transport in biological systems.