A) What information will a hydropathy analysis about a predicted membrane protei

Question

A) What information will a hydropathy analysis about a predicted membrane protein give you?

B) How can a scientist distinguish between a singlepass integral membrane protein with only its N-terminus exposed on the extracellular surface and a multipass integral membrane protein with only three hydrophilic loops exposed on the extracellular surface?

C) Would a scientist be able to determine if a protein is fatty acylated or GPI-anchored protein using hydropathy analysis?

D) What information could a scientist determine from a FRAP experiment?

E) You were examining the mobility of two different unknown integral plasma membrane proteins, proteins X and protein Y. In one cell, you fluorescently label the X proteins. In another cell, you label all the Y proteins. When you perform FRAP analysis on both cells, you find that most of the protein X fluorscence has recovered within 3 minutes, but recovery of the protein Y fluorescence us significantly slower. Explain what results tell you about mobility of the X and Y proteins, and propose a possible explanation for why the mobilities of the two proteins differ.

For a particular cell at 25 degress C, the concentration of sucrose is 10mM on the inside of the cell and 0.5 mM on the outside, whereas the concnetration of sodium ions (Na+) is 0.5mM on the inside of the cell and 10mM on the outside. The membrane potential is -150mV

Constants: R=1.987cal/mol-K; T=25C=298K; F= 23,062cal/mol-volt

What is the delta G for the inward transport of sucrose?

What is the delta G for the inward transport of sodium ions?

What would be the net delta G for the coupling of these two reactions?

Explanation / Answer

a) Hydropathy plot is a method to display the hydrophobic and hydrophilic regions of a protein sequence and predict the structure based on these regions. In othr words it is useful in determining the ydrophobic interior portions of globular proteins and determines membrane spanning regions on membrane proteins. about membrane protein, it tells that an integral membrane protein has a stretch of about 20 hydrophobic amino acids on the surface to enable it to pass through membrane lipid bilayer.

b) Single pass integral membrane and multipass integral membrane protein can be identified using Hydropathy plot.  A hydropathy plot reveals one or more regions with a high hydropathy index. For multipass integral membrane protein, the plot will show three distinct peaks revealing the presence of 3 transmembrane segments and for single pass integral membrane protein their will be only one peak indicating the presence of only one hydrophobic segment.

d) The lateral movement of membrane proteins can be seen by fluorescence microscopy through the technique termed as Fluorescence recovery after photobleaching (FRAP). FRAP exeriment showed that the membrane proteins can move freely in the lipid bilayer.

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