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Bio 201 - Cell Biology Dr. Hutson. Lecture 20 – Review March 14, 2014. Review topics. Motor proteins Signal transduction all Other. Signal transduction: what it is. How cells interpret (i.e. “transduce”) signals from other cells.
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Bio 201 - Cell BiologyDr. Hutson Lecture 20 – Review March 14, 2014
Review topics • Motor proteins • Signal transduction all • Other
Signal transduction: what it is • How cells interpret (i.e. “transduce”) signals from other cells. • Involves ligand binding to a receptor, usually on the cell surface. • High affinity • Specificity • Conformational change in receptor is key to intracellular response. • Intracellular response often involves complex, multi-step pathways • Sometimes involves a second messenger: soluble molecule produced in response to ligand binding; responsible for activation of next step in pathway
“Modes” of signaling between cells • Juxtacrine and Contact-dependent: very fast and specific to cells in immediate surroundings • Paracrine: relatively fast, affects more cells • Endocrine: much slower, affects many different cells throughout organism; good for coordinating cellular responses
Different ligands may bind to different types of receptors. Different receptors transduce qualitatively different types of responses. GPCRs: Many different types of ligands • Response to ligand binding usually involves changes in enzyme activity • Relatively fast • Reversible • Response amplification AC α β Υ cAMP enzymes PKA Many different responses RTKs: Growth factors • Response to ligand binding usually involves changes in transcriptional activity • Slower • Not necessarily reversible • b/c enzymes involved, amplification ras txn MAPK Growth, proliferation
Different ligands may bind to different types of receptors. Different receptors transduce qualitatively different types of responses. Steroid hormone Rs: Steroid hormones • Response to ligand binding almost always involves changes in transcriptional activity • Slower • Not necessarily reversible • No amplification (no enzymes) txn Many different responses, incl. growth, differentiation
The same ligand may have different effects on different types of cells. This is sometimes due to the fact that different cells have different targets of Gα. Liver: Epinephrine α β AC Υ Glycogen breakdown glucose cAMP enzymes PKA Some blood vessels and sweat glands: Epinephrine PLC α β Υ Contraction (some blood vessels); Secretion (sweat glands) IP3 Ca++
In other cases, it is due to the fact that different cells have different targets of PKA. Liver: Epinephrine α β AC Υ Glycogen breakdown glucose cAMP PKA Bronchial smooth muscle cells: Epinephrine α AC β Υ Bronchodilation cAMP PKA
Analyzing the effects of activators and inhibitors α AC Υ Epinephrine β GTP cAMP PKA Glycogen breakdown glucose (and inhibition of glycogen production)
Motor proteins - Myosin Function: Muscle contraction, actin retraction in amoeboid cells Interacts with: actin Direction: + end directed - + Myosin is anchored - + ATP binds - +
Motor proteins - Kinesin Function: Organelle transport Interacts with: Microtubules Direction: + end directed - + Kinesin is bound to vesicle or organelle (NOT anchored) ATP binds - +
Motor proteins - Dynein Function: Organelle transport; cilia and flagella Interacts with: Microtubules Direction: - end directed Mechanistically similar to kinesin, but going in the opposite direction.
