SIGNAL TRANSDUCTION MECHANISMS Flashcards
What does the signal represent?
information detected by specific receptors & converted to a cellular response, which involves a chemical process.
Signal transduction
The conversion of information into a chemical change.
Stages of signaling
- Reception
- Transduction
- Response
- Resonpse
Ion transport. Protein modification
(phosphorylation of target proteins, which changes their activities). Gene expression
Signals
*Antigens * Light * Developmental signals * Mechanical contact * Growth factors * Neurotransmitters * Hormones * Food
Signals 2
- ECM components * Odorants * Gustatory (Taste) * Pheromones * Cell surface glycoproteins / oligosaccharides
Features of signal transduction systems
- Specificity * Sensitivity * Amplification * Desensitization-adaptation * Integration
Specificity
signal molecule fits binding site on its complementary receptor; other signals don’t fit
amplification
when enzymes activate enzymes, the number of affected molecules increases geometrically in an enzyme cascade
desensitization / adaptation
receptor activation triggers a feedback circuit that shuts off the receptor/removes it from the cell surface
When a signal is present continuously, the receptor system is turned off
desensitization
When the stimulus falls below a certain threshold, the system again becomes sensitive
adaptation
Integration
when 2 signals have opposite effects on a metabolic characteristic like the concentration of a 2nd messenger X, or there membrane potential Vm, the regulatory outcome results from the integrated input from both receptors
ability of the system to receive multiple signals and produce a response appropriate to the needs of the cell or organism.
Integration
Importance of Lipid Rafts
Rafts sequester groups of signaling proteins & receptors in small regions of the plasma membrane, enhancing their interactions & making signaling more efficient.
Gated ion channels
Change cytosolic concentration of an ion (like Ca2+) which then serves as a 2nd messenger. or change transmembrane electrical potential
Acetylcholine Receptor Is a Ligand-Gated Ion Channel
Ach receptor is an allosteric protein with two high affinity binding sites for Ach.
Ach in the synaptic cleft
quickly removed by acetylcholinesterase (AChE). When Ach remains high for few milliseconds/+, receptor is desensitized.
G Protein-coupled receptors (GPCR)
Plasma membrane receptor with 7 transmembrane helical segments (serpentine receptor).vCytoplasmic part of receptor interacts with a guanosine nucleotide- binding protein (G protein).
G Protein-coupled receptors (GPCR) 2
G protein is a heterotrimeric protein including alpha, beta & gamma subunits. Inactive when GDP is bound to G alpha
G Protein-coupled receptors (GPCR) 3
When ligand (hormone) binds to its receptor, conformational change in the receptor occurs that stimulates G protein complex : Galpha subunit releases GDP & binds GTP & becomes active.
G Protein-coupled receptors (GPCR) 4
GTP-bound alpha subunit becomes activated, dissociates from receptor & binds to target enzyme, altering its activity. Target enzyme can be adenylyl cyclase, phospholipase C
G Protein-coupled receptors (GPCR) 5
Galpha has intrinsic GTPase activity that turns itself off by converting bound GTP>GDP. Inactive Galpha (GDP-bound) dissociates from enzyme & reassociates with beta gamma dimer>inactive Galpha is again available to interact with hormone bound receptor.
Amplification of the signal:
Adrenaline (epinephrine) is a hyperglycemic hormone that increases blood glucose by stimulating degradation of glycogen. Adrenaline triggers activation/ phosphorylation cascade & signal is amplified at every step of the cascade.
