**Core Concept**
The alpha helix is a fundamental structure in protein folding, characterized by a spiral conformation where each amino acid is covalently bonded to its neighbors through peptide bonds. This structure is stabilized by hydrogen bonding between the carbonyl oxygen of one amino acid and the amide hydrogen of another, approximately four residues away.

**Why the Correct Answer is Right**
The alpha helix is a right-handed spiral structure, where each amino acid is positioned approximately 3.6 angstroms away from the next, with a hydrogen bond forming between the carbonyl oxygen of one amino acid and the amide hydrogen of the fourth preceding amino acid. This specific arrangement of hydrogen bonds and peptide bonds gives the alpha helix its stability and unique properties.

**Why Each Wrong Option is Incorrect**
**Option A:** This option does not specify any structure, making it an ambiguous choice.
**Option B:** This option is incorrect because the beta sheet is a different type of protein secondary structure, characterized by a sheet-like conformation.
**Option C:** This option is incorrect because the beta turn is a type of protein secondary structure that connects two beta strands, but it does not describe the alpha helix.

**Clinical Pearl / High-Yield Fact**
The alpha helix is a key component of many proteins, including enzymes, hormones, and structural proteins, and understanding its structure is crucial for understanding protein function and disease mechanisms.

**Correct Answer: C. Beta turn.