Final answer:
Hydroxylysine is the critical amino acid important for the crosslinking of collagen trimers, providing strength and stability to the collagen structure within connective tissues.
Step-by-step explanation:
The amino acid critical for the crosslinking of collagen trimers is hydroxylysine. Collagen consists of a triple helix structure with a repeated sequence of Gly-X-Y. In this sequence, 'X' is often proline, and 'Y' is frequently hydroxyproline or hydroxylysine. These two amino acids play vital roles in the stability and strength of the collagen triple helix. Hydroxylysine, in particular, undergoes further modification which allows it to form cross-links between collagen molecules, providing tissue with additional tensile strength.
The hydroxylation of lysine residues, which creates hydroxylysine, is a posttranslational modification requiring specific enzymes such as lysyl hydroxylase, with ascorbic acid serving as a cofactor. Without hydroxylysine and its ability to crosslink, the structural integrity of collagen fibers would be compromised, leading to weaker connective tissues. Therefore, hydroxylysine is indispensable for the proper functioning and structure of collagen in the human body.