When vesicles of the cardiac sarcoplasmic reticulum (CSR) are incubated with ATP Mg^2+ and Ca^2+, they take up Ca^2+ and reach a
pseudo steady-state. This is a steady state that changes, but slowly. The uptake of Ca2+ is mediated by the SERCA2a Ca-ATPase. The uptake reaction can be quenched by adding EGTA to the external solution, which binds the Ca^2+ outside of the vesicles, or by adding glucose plus hexokinase, that converts the ATP to ADP and glucose-6 phosphate. When the uptake reaction is stopped, Ca^2+ that was already taken up by the vesicles leaks out passively A. The amount of Ca^2+ taken up by the vesicles is generally normalized to the amount of CSR protein in mg rather than being expressed as a concentration. A typical steady state Ca2 uptake is 40 nmol mg^-1. In separate experiments, the enclosed volume of the CSR vesicles was determined to be 5 mu L mg. What is the approximate concentration of Ca^2+ inside the vesicles at steady-state? The total Ca^2+ concentration is its amount divided by the volume in which it is distributed. In this case the amount is 40 nmal mg CSR protein^-1 and the volume is 5 mu L mg CSR protein^-1, The concentration is estimated as B. The average vesicle size determined by electron microscopy is about 150 nm. What is the volume and surface area of a vesicle this size, assuming it is a sphere? C. Given that the enclosed volume of the aggregate vesicles is 5 iL mg-1, how many vesicles are there per mg of CSR protein? How much surface area is there per mg of CSR protein? D. The initial passive efflux at a load of 40 nmol mg when the pump is stopped is 16 nmol min^-1mg^-1. Convert this to a flux in units of nmol cm^-2 s^-1 by dividing by the surface area per mg of CSR protein and converting min to s. E. What is the passive permeability to Ca^2+ in cm s^-1?
1 answer:
Answer
I added 4 and 5 as an attachment due to time constraint.
Explanation:
1. at a steady state ca2+ taken by vesicle = 40n/mol
enclosed volume of CSR = 5μ/mg
concentration of ca2+ in vesicle =
40*10⁻⁶/5x10⁻⁶
= 0.008
= 8x10⁻⁹mol/L
2. radius of circle =75nM
volume = 150nm
volume of vesicle = 4/3 x pi x r³
= 1.33 x 3.14 x (75x10⁻⁹)³
= 1.77 x 10⁻²¹
when we convert this we get
1.77x10⁻¹⁸L since 1m³ is equal to 100oL
surface area =4x3.14x(75x10⁻⁹)²
= 12.56x5.625⁻¹⁵
= 7.065x10⁻¹⁴m²
this is 7.065x10⁻¹⁰cm²
3. number of vesicle/CSR
= 5x10⁻⁶/1.77x10⁻¹⁸
= 2.824x10¹²
surface are = 2.824x10¹² x7.06x10⁻¹⁰
= 19.95x10²
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