Please explain in detail thanks 1. Compared and contrast intracellular signaling
ID: 36792 • Letter: P
Question
Please explain in detail thanks
1. Compared and contrast intracellular signaling by receptor tyrosine kinase and G- protein receptor. Discuss how these receptors are activated respectively and name at least 2 downstream targets for each kind of receptor. Also name one example for each kind of receptor of a physiological process is activated via these receptor.
2. Discuss the role of calcium in the contraction of striated skeletal muscle contraction and smooth muscle. Clearly discuss how Ca2+ release is triggered and the effects of the Ca2+ inside the cell in each case. Also discuss why sometimes a person may experience some involuntary
Explanation / Answer
Answer:
1)
G-protein-linked receptors bind a ligand and activate a membrane protein called a G-protein. The activated G-protein then interacts with either an ion channel or an enzyme in the membrane. All G-protein-linked receptors have seven transmembrane domains, but each receptor has its own specific extracellular domain and G-protein-binding site.
Cell signaling using G-protein-linked receptors occurs as a cyclic series of events. Before the ligand binds, the inactive G-protein can bind to a newly-revealed site on the receptor specific for its binding. Once the G-protein binds to the receptor, the resultant shape change activates the G-protein, which releases GDP and picks up GTP. The subunits of the G-protein then split into the ? subunit and the ? subunit. One or both of these G-protein fragments may be able to activate other proteins as a result. Later, the GTP on the active ? subunit of the G-protein is hydrolyzed to GDP and the ? subunit is deactivated. The subunits reassociate to form the inactive G-protein, and the cycle starts over .
The tyrosine kinase receptor transfers phosphate groups to tyrosine molecules. Signaling molecules bind to the extracellular domain of two nearby tyrosine kinase receptors, which then dimerize. Phosphates are then added to tyrosine residues on the intracellular domain of the receptors and can then transmit the signal to the next messenger within the cytoplasm.
2)
Cardiac-muscle cells are striated, and are a lot like skeletal-musclecells except that in cardiac muscle, the fibers areinterconnected. Thesarcoplasmic reticulum of cardiac-muscle cells is not as well-developed as that of skeletal-muscle cells. Cardiac-muscle contraction is actin-regulated, meaning that the calcium ions come both from the sarcoplasmic reticulum (as in skeletal muscle) and from outside the cell (as in smooth muscle). Otherwise, the chain of events that occurs in cardiac-muscle contraction is similar to that of skeletal muscle.
Compared to skeletal muscle,smooth-muscle cells are small. They are spindle-shaped, about 50 to 200 microns long and only 2 to 10 microns in diameter. They have no striations or sarcomeres. Instead, they have bundles of thin and thick filaments (as opposed to well-developed bands) that correspond to myofibrils. In smooth-muscle cells, intermediate filaments are interlaced through the cell much like the threads in a pair of "fish-net" stockings. The intermediate filaments anchor the thin filaments and correspond to the Z-disks of skeletal muscle. Unlike skeletal-muscle cells, smooth-muscle cells have no troponin, tropomyosin or organized sarcoplasmic reticulum.
As in skeletal-muscle cells, contraction in a smooth-muscle cell involves the forming of crossbridges and thin filaments sliding past thick filaments. However, because smooth muscle is not as organized as skeletal muscle, shortening occurs in all directions. During contraction, the smooth-muscle cell's intermediate filaments help to draw the cell up, like closing a drawstring purse.
Calcium ions regulate contraction in smooth muscle, but they do it in a slightly different way than in skeletal muscle:
This process is called myosin-regulated contraction.
3)
Role of the endocannabinoid system in synaptic plasticity in the hippocampus
Neuronal activity is a potent stimulus for endocannabinoid synthesis and release . Once released by the postsynaptic neurons, endocannabinoids travel retrogradely across the synapse to bind presynaptic CB1R, suppressing neurotransmitter release at both excitatory and inhibitory synapses in a short- and long-term manner. Activation of CB1R and subsequent long-term inhibition of transmitter release defines endocannabinoid-mediated long-term depression (eCB-LTD).
When eCB-LTD occurs at inhibitory terminals (I-LTD), it can facilitate the induction of long-term potentiation (LTP) at excitatory inputs. Nevertheless, CB1R also mediates short-term plasticity, as in the case of depolarization-induced suppression of inhibition or excitation (DSI or DSE, respectively).
In the same target cell, the difference between eCB-LTD and eCB-DSI/DSE relies on the duration of CB1R activity, which engages distinct signalling events in the neuron, leading to a short or long suppression of neurotransmitter release . A role for intracellular CB1R and mitochondrial mechanisms has been recently reported for eCB-DSI in the hippocampus .
On the other hand, the ECS can be directly modulated by exogenous cannabinoids. In this regard, the exposure to a single administration of THC abolished eCB-LTD and I-LTD when measured in hippocampal slices obtained the next day after cannabinoid administration, an effect that was reversed to control conditions when the electrophysiological recordings were performed 3 days after THC administration.
More recently, a critical role for astroglial CB1R was revealed using in vivo recordings of cannabinoid-induced LTD (CB-LTD) at hippocampal CA3