Chapter 4: Problem 7

Explain how an \(\alpha\) helix can be amphipathic.

Short Answer

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Answer: An α-helix is amphipathic when it is composed of alternating hydrophilic and hydrophobic amino acids, with the hydrophilic residues facing the solvent and the hydrophobic residues facing the interior of the protein structure. This amphipathic property is essential for many protein functions, such as membrane proteins that span lipid bilayers and soluble proteins that interact with diverse molecules. It allows the helix to be soluble in aqueous environments while also being able to interact with nonpolar regions of other molecules or within the protein itself.

Step by step solution

Understand amphipathic properties

Amphipathic molecules contain both hydrophilic (polar or charged groups that can form hydrogen bonds with water) and hydrophobic (nonpolar groups that do not form hydrogen bonds with water) regions.

Learn the structure of an α-helix

An α-helix is a secondary structure of proteins where the peptide backbone forms a helical structure in which the N-H group of an amino acid donates a hydrogen bond to the C=O group of another amino acid, four residues earlier in the amino acid sequence. The helix is right-handed, and each turn of the helix contains around 3.6 amino acid residues.

Understand the arrangement of amino acid residues in an α-helix

In an α-helix, the amino acid residues are arranged in such a way that the hydrophilic and hydrophobic residues can be separated along the helical axis. The side chains of the amino acids in the helix extend outwards from the peptide backbone, allowing the hydrophilic and hydrophobic residues to cluster on opposite sides of the helix.

Explain the amphipathic nature of an α-helix

An α-helix can be amphipathic when it is composed of alternating hydrophilic and hydrophobic amino acids, with the hydrophilic residues facing the solvent and the hydrophobic residues facing the interior of the protein structure. This arrangement allows the helix to be soluble in aqueous environments while also being able to interact with nonpolar regions of other molecules or within the protein itself. This amphipathic quality is essential for many protein functions, such as membrane proteins that span lipid bilayers and soluble proteins that interact with diverse molecules.

Look at an example of an amphipathic α-helix

One common example of an amphipathic α-helix is the helical region in membrane proteins. In these proteins, the hydrophobic residues face the lipid bilayer, while the hydrophilic residues face the aqueous environment of the cell's interior or exterior. This arrangement allows for stable interactions with both the lipids and water, enabling the protein's proper function within the membrane.

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Explain how an \(\alpha\) helix can be amphipathic.

Short Answer

Step by step solution

Understand amphipathic properties

Learn the structure of an α-helix

Understand the arrangement of amino acid residues in an α-helix

Explain the amphipathic nature of an α-helix

Look at an example of an amphipathic α-helix

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