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-   -   help with biochem problems, any bio/chem people out there!! (http://archives1.twoplustwo.com/showthread.php?t=559125)

 jgallardo 12-02-2007 03:57 AM

help with biochem problems, any bio/chem people out there!!

Hey, if any of you have taken biology/chemistry courses and can help me with my biochem homework or part of it, I'd appreciate it. My professor phrases questions in a somewhat odd manner, but here goes:

There is a cartoon that goes along with the question, but basically there is a liposome with these given facts:

membrane potential: -70mV (-0.07V)
temperature: 37 degrees celsius (310K)
Internal ion concentrations: [K+]=140mM , [Na+]=12mM
External ions: [K+]=4mM, [Na+]=145mM
there is an N+K+ATPase transport protein in the bilayer, intake: 2K+; pump out: 3Na+
outer diameter of liposome is = 0.5 micrometers (µm = 10^-6)

(1) A liposome contains 10 glycogen molecules, each molecule on average contains 10,000 glucose unit. If all glycogens are broken down to glucose, how does osmotic pressure inside the liposome CHANGE?

osmotic pressure pi = nRT/V. pi is in unit of atmosphere, T in Kelvin, R is the gas constant, n is the moles of molecules and V is effective volume in liter. MW of glucose is roughly 180 Dalton.

(2) The cartoon shows the resting state of a liposome. Under such condition, what is deltaG of Na+K+ATPase undergoing one cycle of reaction (pump out 3 Na+ and intake 2 K+, Pg 304)? How efficient of the ATP fuel is utilized?

(3) In an alternative design of experiment, liposomes contain no glycogen nor glucose but gluose utilization enzymes to power the Na+K+ATPase. The liposomes also have glucose transporters on it membrane to facilitate inward diffusion of glucose. A series of glucose solutions are quickly mixed with liposome and the initial intake velocity, v0, is measured (Table 1). Assuming the transporter works like a Michaelis-Menten-like enzyme, calculate Vmax and Km.

(4) Table 1 also includes measurement of the transporter kinetics in the presence of 4 µ compound X. Calculate kinetic parameters (eg. alpha, alpha, KI or KI) and use kinetics to explain possible mechanism of this inhibitor.

[glucose] (mM), no inhibitor: v0 (µM/s), 4uM inhibitor: v0 (µM/s)
1, 2.5, 1.0
2, 4.0, 1.8
5, 6.3, 3.6
10 , 7.6 , 5.3
20, 9.0, 6.9

(5) Glucose undergoes glycosis that generates ATP molecules directly fueling the Na+K+ATPase to pump ions. How many glucose molecules need to be broken down to reduce the cytosolic Na+ concentration to 10 mM? (assuming membrane potential does not change and liposomes only occupy a small fraction of volume of suspension)

Thanks, if you can lead me in the right direction or help me.

 jgallardo 12-02-2007 04:13 AM

Re: help with biochem problems, any bio/chem people out there!!

For question 1, i've used the equation to find pi, the osmotic pressure, but i think i'm wrong in my calculations of n.
i'm using R = 0.08206 L-atm/K-mol
T =310K
V = 6.545 x 10^-17L (i used the outer diameter given to find the volume of a sphere)

n is confusing me, because since the 10 glycogen are broken down into 10000 glucose each, it seems as if the osmotic pressure would increase 10000 fold. i'm not sure if this is a correct assumption.

2. i used the equation for deltaG = RTln( [A+] in/ [A+] out ) + ZF?
F= faraday constant = 96485 C/mol
R=8.314 J/Kmol
T=310 K
Z = 1 (ionic charge of the molecules)

I also multiplied the K one by 2 because there were 2 molecules goin into the liposome, and for the Na I multiplied the answer is got by 3 because there were 3 molecules taken out of the liposome.

 kevin017 12-02-2007 05:14 AM

Re: help with biochem problems, any bio/chem people out there!!

1. seems like 10000 fold increase

5. think about this. you're changing the concentration from 12mM to 10mM, so you need to expel 2 mM of Na, which takes how many mM of ATP, which is generated by how many mM of glucose?

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