(N/A) Proteins are macromolecules formed by the polymerization of amino acids.
Structurally,proteins are divided into four levels:
$1$. Primary structure: It is the linear sequence of amino acids in a polypeptide chain.
$2$. Secondary structure: The polypeptide chain is coiled to form a three-dimensional structure.
$3$. Tertiary structure: The helical polypeptide chain is further coiled and folded to form a complex structure.
$4$. Quaternary structure: More than one polypeptide chains assemble to form the quaternary structure.
Milk contains many globular proteins. When milk is converted into curd or yoghurt,these complex proteins undergo denaturation. During this process,the secondary and tertiary structures of the proteins are destroyed,causing the globular proteins to unfold and coagulate,which gives curd its characteristic texture.