Insulin is

Which one of the following is not a fibrillar protein?

Which amino acids have polar and positively charged $R$ groups?

The exoskeleton of birds and mammals is composed of which biomolecule?

Which one is the most abundant protein in the animal world?

The triple helical structure of collagen was published in Nature in $1954$, and the analysis of the allowed conformations of proteins was performed through the use of the: