Final answer:
Glycine has a low propensity to form alpha helix because it lacks a side chain.
Step-by-step explanation:
The low propensity of glycine to form alpha helix is due to the fact that glycine lacks a side chain. The side chains of amino acids play a crucial role in stabilizing the alpha helix structure through hydrogen bonding. Without a side chain, glycine is too flexible to form the stable, rigid structure of an alpha helix.