Final answer:
The length of the peptides that bind to MHC Class I is determined by the length of the α protein chain.
Step-by-step explanation:
MHC Class I molecules consist of a longer α protein chain coupled with a smaller β₂ microglobulin protein. The length of the α protein chain determines the length of the peptides that bind to MHC Class I.
The α protein chain folds into three separate domains: α₁, α₂, and α₃, and the antigen-binding cleft is formed by the α₁ and α₂ domains. Therefore, the length of the peptides that bind to MHC Class I is determined by the length of the α protein chain.