Identify a protein present in nails

$A$ polypeptide can be called a protein when its mass is

The $\alpha$-helix structure is found in which of the following?

The bond that determines the secondary structure of a protein is

Which structure of protein remains intact after coagulation of egg white on boiling?

Identify the $N$-terminal and $C$-terminal $\alpha$-amino acids respectively in the following polypeptide fragment: $Ala-Gly-Ser-Tyr-Gly$.