The telephone cord may well illustrate the idea of protein structures.
Form and function: an inseparable binomial
You will soon understand how the spatial structure of a protein is related to its biological function. For the time being, remember that the maintenance of secondary and tertiary structures is due to the bonds that occur between amino acids within the protein molecule, determining the different spatial aspects observed.
O heating a protein to certain temperatures promotes the breakdown of internal bonds between amino acids, responsible for the maintenance of secondary and tertiary structures. Amino acids do not separate, they break peptide bonds, but the protein is "dismantled", loses its original structure. We say that a protein denaturation occurred, with loss of its original form. In this way the biological function of the protein is impaired.
However, it is not always the temperature or the change in the acidity of the medium that causes the shape of the protein to change. Oftentimes, substitution of a single amino acid can change the shape of the protein.
An important example is the substitution of hemoglobin, of the amino acid glutamic acid by the amino acid valine. This simple change causes a profound change in the shape of the entire hemoglobin molecule, directly interfering with its ability to carry oxygen.
Red blood cells containing altered hemoglobin acquire the shape of a sickle when subjected to certain conditions, which gave the name to this anomaly: sickle cell anemia.