KEY POINTS
1. All physiological change is mediated by proteins.
2. Protein function depends on protein shape and shape changes.
3. A series of enzymatic reactions converts tyrosine into the signaling molecules dopamine, norepinephrine, and epinephrine.
4. Muscle contraction and its initiation and cessation depend on the binding specificity and allosteric properties of proteins.
5. Biological membranes are a mosaic of proteins embedded in a phospholipid bilayer.
Transport
1. Only small, uncharged molecules and oily molecules can penetrate biomembranes without the aid of proteins.
2. Molecules move spontaneously from regions of high free energy to regions of lower free energy.
3. Important transport equations summarize the contributions of the various driving forces.
4. Starling's hypothesis relates fluid flow across the capillaries to hydrostatic pressure and osmotic pressure.
5. Membrane proteins that serve the triple functions of selective transport, catalysis, and coupling can pump ions and molecules to regions of higher free energy.
6. Many membrane proteins selectively facilitate the transport of ions/molecules from high to low electrochemical potential.
7. Passive transport of K+ across the plasma membrane creates an electrical potential.
8. Spatial organization of active and passive transport proteins enables material to pass completely through the cell.
9. Membrane fusion allows for a combination of compartmentalization and transport of material.
Information Transmission and Transduction
1. Cell signaling often occurs by a lengthy chain of sequential molecular interactions.
2. Signaling pathways begin with the binding of an extracellular molecule to a receptor.
3. Specific physiological information is inherent in the receptor/ligand complex, not in the hormone/neurotransmitter molecule.
4. G-protein-coupled receptors are the largest family (a "superfamily") of receptors and help regulate almost all physiological processes.
5. Most G-protein-linked information is sent to the cytoplasm by "second messengers."
6. Ca2+ transport across plasma and intracellular membranes is an important second messenger.
7. CycIicAMP is produced by activation of a membrane-bound enzyme in response to hormone/neurotransmitter binding to receptors.
8. The receptor-mediated hydrolysis of a rare phospholipid of the plasma membrane produces two different second messengers with different actions.
9. Steroid hormones and other lipid signals interact with nuclear receptors, which are transcription factors within the cell.