An unstimulated mammary epithelial cell at steady state has approximately 10^5 EGFR molecules on its surface. Using radiolabeled EGF, you calculate a basal internalization rate of 0.01 min-1 for EGFR on unstimulated cells.
a) Assuming all of the internalized receptors are degraded, how many receptor molecules does the cell synthesize per minute?
b) When mammary epithelial cells are exposed to saturating concentrations of EGF (so that all receptors are bound), the rate of internalization increases by 5-fold. Once the stimulated cells reach equilibrium, how many receptors will be on the surface of each cell?
c) Given your calculations, what is the average time (i.e. half-life) each receptor molecule will spend on the cell surface under the unstimulated or stimulated conditions?
a.Since the basic internalization rate is 1 in 100 molecules in one minute. therefore, 1000 molecules will be degraded out of 10^5 molecules with the given rate. to maintain the steady state the cell will have to synthesize 1000 EGFR molecules.
b. since the internalization rate increases by 5 fold, therefore there will be 5 x 10^3 molecules degraded. therefore post equilibrium, there will be .95 x 10^5 or 95,000 EGFRs left on the surface.
c. under unstimulated conditions, 0.01 molecules are internalised in 1 minute therefore amount of time to internalize for 1 molecule will be = 1min/0.01 *1 molecule = 100 minutes
in an stimulated environment, since the internalization rate increases to 0.05, therfore, based on calculations = 1min/0.05 *1 molecule = 20 minutes
An unstimulated mammary epithelial cell at steady state has approximately 10^5 EGFR molecules on its surface....