Hillard Flashcards
Initiators of cell signaling
Overview
- much of cell signaling initiated by binding of small molecules to receptors
- difference in distance from site of release and target define the types of signaling
- different time courses
Ionotropic receptors TRP channels
NT’s and sensory stimuli utilize this cell signaling method
The receptor transducer and amplifier are combined and release messengers such as Ca2+, Na+, and Cl-
Voltage-operated calcium channels
Electrical signals like membrane depolarization active use these
Change in membrane potential (depolarization) opens Ca2+ channels flowing the cell with Ca2+ which acts as a messenger
GPCR
Acted on by NTs and hormones
- GPCR is bound by ligand
- conformational change in alpha and beta/gamma subunit inside cell GDP exchanged for GTP
- signal amplified by AC
- AC stimulates production of cAMP
Or amplifier is PLC and second messengers are DAG and InsP3 and Ca2+
Genomic and nongenomic action of steroid hormones
Both of these happen in the cell
Genomic action: receptor, transducer, and messenger are all in one and the amplification is through regulation of gene transcription
Nongenomic action: GPCR
Tyrosine kinases and serine/threonine kinases
TK: Growth and survival factors
Use transducers, amplifiers and messengers
S/T Kinases: transforming growth factor B superfamily
Combined transducer and amplifier
Summary of chemical cell signaling
- greater variety of ligands and signaling motifs
- effective way to interfere selectively with a signaling pathway is to mimic or inhibit the ligand binding event
- trying to alter signaling motif can result in off target effects
Small molecular weight amines as ligands
- ACh, glutamate, NE, and dopamine
- stored and released in vesicles
- mech for tight regulation of amount released; inactivation
- fast or medium transmission
Lifecycle of ACh
- ACh synthesized by ChAT
- packaged into vesicles by VAChT
- once in synapse used to signal or degraded by AChE
- AChE degrade ACh into acetate and choline
- Choline imported back into the cell via the CHT (choline transporter)
- CHT rate-limiting step of this process
- Neuromuscular junction used ACh
- Release from vesicles is regulated by calcium
Pathway of epinephrine synthesis
Tyrosine (TH with cofactor TTHP) > DOPA > Dopamine > NE > Epinephrine
First rxn is rate-limiting step
Peptides as ligands
- Common in nervous system
- Large
- Not released using synaptic vesicles but through secretory pathway
- synthesized as large precursors
(example: chemokines)
Lipid signaling molecules
- membrane soluble
- made on demand
- derivatives of arachidonic acid
- targets can be intracellular and membrane
EX: 2-arachidonoylglycerol (2-AG)
Gaseous molecules
-can diffuse freely through membranes and water
EX: NO (important transmitter in vasculature)
Steroid hormones
Cholesterol can be converted into cortisol or aldosterone
PARs
- thrombin receptors
- important in blood clotting
- ligand is part of receptor
- peptide ligand gets cleaved off by thrombin causing activation of receptor
Equation explaining ligand and receptor relationship
Ligand + Receptor = LR complex = effect
What does binding involve?
- overcoming Brownian motion of the ligand in solution
- breaking H bonds between ligand and water
- energy required to transduce the receptor
Ligand binding to receptor and the law of mass action
Law of mass action: proposition that the rate of a chemical reaction is directly proportional to the product of the activities or concentrations of the reactants
k1: rate constant for association
k2: rate constant for dissociation
Equilibrium
k1 [L] * [R] = k2 [LR]
k2 / k1 = [L] * [R] / [LR]
k1 / k2 = Kd
Kd
- Equilibrium dissociation constant
- goodness of fit
- inversely related to affinity of L for receptor
- units are concentration
- when [L] is large, [LR] = Rt
- when [L] = Kd, [LR] = 1/2 Rt
Fractional occupancy of receptor by ligand at equilibrium
[LR] / Rt
-under most physiological conditions, the fractional occupancies of receptors by their ligands is very small
Saturation binding assay
- performed at equilibrium
- used to determine Kd value for LR complex
- can be used to estimate total # of receptors (Rt)
- determine LR at various conc of L
- if need to determine time to equilibrium, use lowest [L]
Competition among ligands
- Reversible competitive
- Irreversible competitive
- Noncompetitive
- Partial agonist/antagonist
Random Tidbits
-Usually, all receptors do not need to be bound to produce maximal effect
