PLEASE HELP WITH BIOCHEMISTRY, HYDROPHOBIC EFFECT!!! THANK YOU IN ADVANCE . :) 5

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PLEASE HELP WITH BIOCHEMISTRY, HYDROPHOBIC EFFECT!!! THANK YOU IN ADVANCE . :)

5. Application: Hydrophobic effect and drug efficacy Data for this problem are from: MacCallum JL Tieleman DP. Computer simulation of the distribution of hexane in a lipid bilayer: Spatially resolved free energy, entropy, and enthalpy profiles. J. Am. Chem. Soc. 2006 128: 125-130 Drugs often need to pass through cell membranes to reach their target biomolecules. Thus drug efficacy is influenced by the solubility of a drug in nonpolar (lipid) vs. polar (blood, cytosol, etc.) environments. Does the hydrophobic effect play a role in this journey from blood stream to target? a) On the Data Sheet, handed out separately, is a model of a lipid bilayer (Fig. 3A). This model is repeated at right. Label the regions of the model that represent polar environments and label the regions that are nonpolar environments. Use the coloring of the various parts of the phospholipid to locate its component structures in the figure at right. The water is shown in red (oxygen) and white (hydrogen) on the sides. b) Many drugs must passively diffuse from the blood stream to inside a cell to bind their molecular target. Which membranes are crossed in this process? c) To explore the drug diffusion process through membranes, researchers placed an n-hexane molecule in this model system, and simulated the molecular dynamics so the n-hexane could wander about. The probability of n-hexane as a function of location in the system could then be determined at several different temperatures. From these probabilities the AG could be determined; the AH could also be determined from the strength of interactions. These results are given in Fig. 3C, with the change in thermodynamic components given relative to the n-hexane being in the bulk water. Using measurements of AH, where was the n-hexane when the system experienced the strongest interactions? Give the position (see scale at bottom of figure) in nanometers from the center ofthe membrane from Panel Cand the part of the membrane at that location from panel A d) Using the thermodynamic data in Panel Cand the membrane model in panel A, where is the n-hexane most likely to be located in this system? Explain

Explanation / Answer

(a)

The hydrophilic part is the water liking part, hence is towards the water side. water is present on the outer part of the molecules in red and white colour on both the sides of the lipid bilayer system. Soo the water along with Chlorine (in yellow) and phosphate( in oramge) represents the hydrophilic or water loving part. where as the hydrophobic parts are in grey ( alkyl chains), and in blue( gycerol and carbonyl groups).

(b)

The drugs in blood pass through a semipermeable membranes which just allow selective absorption of the drug from the fluid stream (i.e. blood stream).

(c)

To find the position of the strongest interaction.

We can say that at the point of strongest interactions, the binding force between the molecules would be the maximum, which would result in decreasing the free movement of the particles and thus the gibbs free energy or the value of delta(G) would zero or positive.

delta(G) = delta(H) - Tdelta(S)

Thus n-hexane was around 2.5nm when it experienced the maximum interactions, as the value of delta(G) i maximum around this location.

(d)

n-hexane would be most likely to be located near the center of the bilayer lipid system, as the value of delta (G) for it is the lest on around that position, Thus n-hexane would be present near the center.

(e)

Given the knowldge the delta(H) and delta (G), researchers could easily calculate the value of delta (S) using the following relation for gibbs free energy for any system:

delta(G) = delta(H) - Tdelta(S),

knowing the temperature of the location we can easily determine the entropy.

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