3. (10 points) Integral membrane proteins, those that are embedded in the membra

Question

3. (10 points) Integral membrane proteins, those that are embedded in the membrane bilayer,
mediate cellular communication, and solute transport across the plasma membrane.
a. How is the amino acid distribution of integral membrane proteins different to
that of soluble proteins? Compare and Contrast.
b. One method of predicting the presence of transmembrane (TM) segments in integral
membrane proteins involves the identification of 20 residue segments that have high
hydrophobicity. Bioinformatics analysis has shown that such an analysis is capable
of identifying possible TM segments with high accuracy when it is known that the
protein is an integral membrane protein. However, the presence of a 20 residue
hydrophobic segment is not a predictor of a protein being an integral membrane
protein versus a soluble protein. Explain these seemingly contradictory
observations.
c. Almost all of the known structures of membrane proteins contain either -helical
transmembrane segments, or -strand TM segments that form -barrels. Membrane
protein do not tend to contain transmembrane segments that lack secondary
structure. Why don’t the transmembrane segments of membrane proteins
unstructured regions (i.e. why are -helices and -barrels the predominant
structures of membrane proteins)?

Explanation / Answer

c) The alpha helix and beta sheets structure give more stability, for a pore like structure facililating transport of molecules in or out of the membrane, they prevent exposure of their hydrophobic aminoacids to the cytocolic water phase.

integral membrane proteins Peripheral membrane proteins also called intrinsic proteins called extrinsic proteins have one or more segments embedded in the phospholipid bilayer donot interact with the lipid bilayer have hydrophobic sidechains tht interact with the lipid bilar no interaction they are membrane spanning localised on the cytosolic side more hydrophobic aminoacids in the internal side of the membrane Hydrophillic aminoacids

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