The amino acid composition of collagen is pivotal for its structural properties. Notably, every third amino acid residue in collagen is glycine, the smallest amino acid. Its size allows for the tight packing of the three polypeptide chains, ensuring structural compactness. Additionally, the presence of proline and hydroxyproline imparts a distinct kinked shape to the chains, adding to the stability of the triple helix. This specific amino acid arrangement, combined with the triple helix configuration, gives collagen its unmatched tensile strength. It's this strength and resilience, attributed to its amino acid composition, that allows collagen to provide robust structural support in various tissues.

The haem group is a prosthetic group embedded in each of the polypeptide chains of haemoglobin. Central to the haem group is an iron atom, which is precisely where oxygen binds. When oxygen binds to the iron atom, it forms a reversible coordinate covalent bond, allowing haemoglobin to pick up oxygen in the lungs and release it in tissues. The presence of these haem groups in all four chains of haemoglobin means the protein can transport up to four oxygen molecules simultaneously, optimising its efficiency. Without the haem group and its iron atom, haemoglobin would be unable to fulfil its primary role in oxygen transport.

Mutations that alter protein structures can significantly impact their function, leading to diseases. For instance, in sickle cell anaemia, a single amino acid mutation in the beta chain of haemoglobin alters the protein's structure. This results in the haemoglobin molecules stacking together under low oxygen conditions, deforming the red blood cells into a sickle shape, which can block blood vessels and cause pain. In other scenarios, misfolded proteins, due to mutations or other reasons, can aggregate, leading to diseases like Alzheimer’s and Parkinson’s. These aggregated proteins can interfere with cell functions, leading to cell death and the associated symptoms of the diseases.

The presence of both A and B chains in the insulin molecule is paramount for its biological function. These two polypeptide chains are linked by two disulphide bonds, and an internal disulphide bond is also present within the A chain. This arrangement ensures the stability of the insulin molecule. Furthermore, the specific positioning and interaction of the A and B chains facilitate the binding of insulin to its receptor on cell surfaces. A disruption in this configuration, either due to mutations or post-translational modifications, can impair insulin's binding efficiency, which, in turn, may impact its ability to regulate glucose levels effectively in the bloodstream.

To unravel the intricate details of protein structures, scientists rely on advanced technologies. X-ray crystallography, for instance, allows for the determination of protein structures at atomic resolutions. In this technique, proteins are crystallised, and then subjected to X-ray beams. The diffraction patterns produced are then analysed to decipher the protein's structure. Another significant technology is cryogenic electron microscopy (cryo-EM), where samples are flash-frozen and examined under electron microscopes, providing high-resolution images. Moreover, bioinformatics tools enable researchers to predict protein structures based on amino acid sequences. Together, these technologies offer a comprehensive view of protein structures, shedding light on their functions and interactions.