What characterizes polypeptide segments that span the lipid bilayer?

What characterizes polypeptide segments that span the lipid bilayer?

• A. They have no peptide bonds
• B. They possess a hydrophilic peptide backbone
• C. They contain a disordered structure
• D. They have no hydrogen bonds

Answer: (B)

Polypeptide segments that span the lipid bilayer are characterized by possessing a hydrophilic peptide backbone. The structure of the lipid bilayer creates a scenario where the hydrophobic tails of the phospholipids repel water and thus any hydrophilic (water-attracting) parts of a molecule. However, segments of polypeptides that penetrate or are embedded within the membrane may be surrounded by hydrophobic regions of the lipid bilayer while retaining some hydrophilic sections. When these polypeptide segments traverse the membrane, the backbone remains hydrophilic, which is essential for stability and interactions with the aqueous environment both inside and outside the cell. This property ensures that the regions of the polypeptide outside the lipid bilayer can engage effectively with other molecules, such as signaling molecules or ions. Additionally, polypeptide segments that span the bilayer often adopt specific structures, such as alpha-helices or beta-sheets, which can be stabilized by intramolecular hydrogen bonding. However, the key characteristic remains the hydrophilicity of the peptide backbone, enabling the polypeptide to navigate through the hydrophobic core of the membrane while maintaining interactions with the external aqueous environments.

Polypeptide segments that span the lipid bilayer are characterized by possessing a hydrophilic peptide backbone. The structure of the lipid bilayer creates a scenario where the hydrophobic tails of the phospholipids repel water and thus any hydrophilic (water-attracting) parts of a molecule. However, segments of polypeptides that penetrate or are embedded within the membrane may be surrounded by hydrophobic regions of the lipid bilayer while retaining some hydrophilic sections.

When these polypeptide segments traverse the membrane, the backbone remains hydrophilic, which is essential for stability and interactions with the aqueous environment both inside and outside the cell. This property ensures that the regions of the polypeptide outside the lipid bilayer can engage effectively with other molecules, such as signaling molecules or ions.

Additionally, polypeptide segments that span the bilayer often adopt specific structures, such as alpha-helices or beta-sheets, which can be stabilized by intramolecular hydrogen bonding. However, the key characteristic remains the hydrophilicity of the peptide backbone, enabling the polypeptide to navigate through the hydrophobic core of the membrane while maintaining interactions with the external aqueous environments.