Proteins perform many different functions in the cell.Their roles depend on their shape and structure.Their molecular shapes can be one of two different types:Fibrous proteins such as collagen, which is a major component of soft tissue, skin and bone, have structural functions.Collagen is a stable molecule with high tensile strength.Fibrous proteins form long parallel chains linked by covalent cross-bridges and hydrogen bonds.Fibrous proteins are usually insoluble or have an insoluble form.Globular proteins such as enzymes and haemoglobin carry out metabolic functions. Enzymes are globular proteins that act as biological catalysts.Their function is dependent on their three-dimensional shape and their solubility.