What happens to the biological activity of a protein due to denaturation?

The total number of carbon atoms present in tyrosine,an amino acid,is $................$

Assertion : Proteins are made up of $\alpha-$ amino acids.
Reason : During denaturation,secondary and tertiary structures of proteins are destroyed.

The dipeptide,$Gln-Gly$,on treatment with $CH_3COCl$ followed by aqueous work-up gives:

Which amino acid from the following contains $-CH_3$ as a side chain?

Protein found in a biological system with a unique three-dimensional structure and biological activity is called a native protein. When a protein in its native form is subjected to a physical change like a change in temperature or a chemical change like a change in $pH$,denaturation of proteins takes place. Explain the cause.