In some -helices, one side is hydrophilic and the other is hydrophobic. Such hel

Question

In some -helices, one side is hydrophilic and the other is hydrophobic. Such helices are termed amphiphilic because they have two different chemical characteristics. The figure to the right depicts just such an amphiphilic helix. The backbone of the peptide is depicted as a ribbon with the side chains projecting outward. One side of the helix has charged side chains extending out and the other side has hydrophobic side chains.

Which of the following statements most accurately describes the orientation of an amphiphilic helix in a folded protein? Note – more than one answer may be correct.

The hydrophobic region of the helix would be oriented towards the outer surface of the protein interacting with the cytoplasm.

The hydrophobic region would be oriented towards the interior of the protein away from the cytoplasm.

The hydrophilic region of the helix would be oriented towards the interior of the protein away from the cytoplasm.

The hydrophobic surface of the protein could be oriented to allow interactions with bilayer and the hydrophilic surface could be lining a channel that transports polar substances

The hydrophobic surface could be oriented to interact with the phosphate backbone of DNA.

Explanation / Answer

In some -helices, one side is hydrophilic and the other is hydrophobic. Such helices are termed amphiphilic because they have two different chemical characteristics.

The following statements most accurately describes the orientation of an amphiphilic helix in a folded protein -

2. The hydrophobic region would be oriented towards the interior of the protein away from the cytoplasm.

It is obvious that the hydrophobic side chains are on one side of the helix would pack into the nonpolar interior of the protein to minimize the free energy. The other side of the helix, which is exposed to the solvent water, containshydrophilic side chains.

And 4. The hydrophobic surface of the protein could be oriented to allow interactions with bilayer and the hydrophilic surface could be lining a channel that transports polar substances.

The membrane-binding amphipathic helix (AH) is a common motif encountered in various proteins and peptides. They usually adopts an orientation parallel to the membrane plane, with its central axis positioned at the level of the lipid glycerol group: hydrophobic residues insert between fatty acyl-chains whereas polar residues face lipid polar heads or the lining of a transporter channel.

Thanks for asking.

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