What is the primary difference between paracrine and endocrine signaling?

Paracrine signals affect nearby cells, while endocrine signals affect distant cells through the bloodstream.

Explain why hydrophobic signaling molecules require carrier proteins in the extracellular space.

Hydrophobic molecules are not water-soluble and thus need carrier proteins to transport them through the aqueous extracellular environment.

Reception, transduction, and response.

GTP replaces GDP on the alpha subunit of the G protein, causing the alpha subunit to dissociate and activate downstream targets.

I can describe the main steps of cell signaling pathways.

1
Autocrine signals affect the same cell that produces them, while paracrine signals affect nearby cells, and endocrine signals affect distant cells.
2
Hydrophobic ligands can diffuse across the cell membrane and bind to receptors inside the cell, whereas hydrophilic ligands bind to transmembrane receptors on the cell surface.
3
The three main classes of transmembrane receptors are G protein-coupled receptors, enzyme-coupled receptors, and ion channel receptors.