 In this way chloroplasts adjust the activity of key processes such as the Calvin–Benson cycle, starch degradation, ATP production and gene expression according to light intensity.Over 90% of the dry weight of hair comprises proteins called keratins, which have a high disulfide content, from the amino acid cysteine.The robustness conferred in part by disulfide linkages is illustrated by the recovery of virtually intact hair from ancient Egyptian tombs.