Which of the following would you expect to be hydrophilic?
A) The interior of a cell membrane
B) A water soluble peptide
C) A triacylglycerol
D) Fatty acid
The correct answer and explanation is:
The correct answer is B) A water soluble peptide.
Explanation:
Hydrophilic means “water-loving” — substances that can interact well with water, usually because they have polar or charged groups that can form hydrogen bonds or ionic interactions with water molecules.
Let’s examine each option:
A) The interior of a cell membrane
- The interior of a cell membrane is made up of the fatty acid tails of phospholipids. These tails are nonpolar and hydrophobic (water-fearing). They avoid water and face inward, away from the aqueous environment inside and outside the cell. So, the interior of a membrane is hydrophobic, not hydrophilic.
B) A water soluble peptide
- Peptides (chains of amino acids) that are water soluble have polar or charged side chains. These groups interact well with water molecules through hydrogen bonding or ionic interactions. Such peptides readily dissolve in water, making them hydrophilic.
C) A triacylglycerol
- Triacylglycerols (or triglycerides) are fats made of three fatty acids attached to glycerol. They are largely nonpolar and do not dissolve in water. They are stored as fat droplets and are hydrophobic.
D) Fatty acid
- Fatty acids have a carboxyl group (-COOH) which is polar and can interact with water, but their long hydrocarbon tail is nonpolar and hydrophobic. This makes them amphipathic (having both hydrophilic and hydrophobic parts). However, generally, fatty acids are considered mostly hydrophobic due to their large nonpolar tail.
Summary:
- Water soluble peptides are clearly hydrophilic because they dissolve in water due to their polar or charged groups.
- The interior of membranes, triacylglycerols, and fatty acids are mostly hydrophobic or amphipathic, but not strongly hydrophilic.
Hence, the best choice here is B) A water soluble peptide.