Molec and Cell 3

signals within a cell

signals between cells

signals that bind other molecules on target cells

Paracrine Endocrine Autocrine Direct signaling across gap junctions

move by diffusion through extracellular matrix examples include synaptic signals and neurotransmitters intercellular

signals from distant cells, typically produce a slower response with a long-lasting effect e.g., hormones intercellular

signaling cells that can also bind to the ligand that is released, such that signal and target cell can be the same or similar to each other e.g., cell death signaling intracellular

intracellular mediators that allow small signaling molecules to move between cells intercellular

hydrophobic signaling molecules that typically diffuse across the plasma membrane and interact with intracellular receptors in the cytoplasm e.g.; DNA and gene expression in nucleus

ligands for these receptors are typically not hydrophobic and would react to the plasma membrane if not for these receptors might be water soluble or gas

Ion channel-linked receptors G-protein-linked receptors Enzyme-linked receptors

ligands that signal the channel to open or close.

ligands that bind to these receptors can help regulate many processes in this case, they help create GTP by hydrolyzing it to GDP, like ATP and ADP

ligands help regulate enzymatic activity e.g.; receptor tyrosine kinase

• ligand binds to enzyme causing it to dimerize • Tyrosine residues on the back end of enzyme on the intracellular domain are then autophosphorylated, triggering a downstream cellular response • signal is terminated by a phosphatase that removes the phosphates from the phosphotyrosine residues

receptors mediating cell-to-cell communication and controlling a wide range of complex biological functions, including cell growth, motility, differentiation, and metabolism

Small hydrophobic ligands so they can diffuse directly across the plasma membrane into the cell, where they interact with internal receptors might be gas or water soluble steroid hormones have similar chemical structures to their precursor, cholesterol

Cholesterol Testosterone Estradiol

Signal transduction Dimerization Signaling pathway Signal integration

when a ligand binds to a receptor and the signal is transmitted through the cell membrane and into the cytoplasm continuing the signal

two receptors bind to each other to form a stable complex

chain of events including second messengers, enzymes and activated proteins that follow ligand binding to a receptor

signals from two or more different cell-surface receptors merge to activate the same response in the cell

epidermal growth factor (EGF) receptor (EGFR) is a receptor tyrosine kinase involved in the regulation of cell growth, wound healing, and tissue repair if EGFR is activated at inappropriate times, uncontrolled cell growth (cancer) may occur