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Old 12-02-2007, 03:57 AM
jgallardo jgallardo is offline
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Join Date: Oct 2006
Location: New York
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Default 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.
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