Final answer:
Collagen units are linked together by a triple helix structure, which is formed by the intertwining of three left-handed collagen peptides, leading to a stable and strong right-handed supercoil. This structure is supported by hydrogen bonds and posttranslational modifications, including hydroxylation and glycosylation, which also contribute to cell communication and tissue integrity within the extracellular matrix.
Step-by-step explanation:
The individual units of collagen are linked together to form a triple helix. This helical structure is made possible by the repeating amino acid sequence Gly-X-Y in each collagen peptide, where 'X' is often proline and 'Y' is frequently hydroxyproline. The hydroxyproline, which is a modified version of proline with an additional hydroxyl (-OH) group, allows for more hydrogen bonding, thereby enhancing the strength of the connective tissues. In the triple helix structure, three left-handed helices are intertwined and displaced along a common axis, resulting in a right-handed supercoil. Posttranslational modifications such as the hydroxylation of proline and lysine, aided by the enzymes prolyl hydroxylase and lysyl hydroxylase, with cofactors including ascorbic acid and a-ketoglutarate, contribute to the stability and strength of the collagen fibrils. Certain hydroxylysyl residues may also undergo further modification by the addition of sugars such as galactose, forming a carbohydrate component called proteoglycans which are interwoven with the collagen fibers in the extracellular matrix, playing a significant role in cell communication and tissue structure.