Cysteine (abbreviated as Cys or C )  is a semi- essential  proteinogenic amino acid with the formula HO 2 CCH(NH 2 )CH 2 SH. It is encoded by the codons UGU and UGC. The thiol side chain in cysteine often participates in enzymatic reactions, as a nucleophile . The thiol is susceptible to oxidization to give the disulfide derivative cystine , which serves an important structural role in many proteins . When used as a food additive, it has the E number E920 .
Cystine is the oxidized dimer form of the amino acid cysteine and has the formula (SCH 2 CH(NH 2 )CO 2 H) 2 . It is a white solid that is slightly soluble in water. It serves two biological functions: a site of redox reactions and a mechanical linkage that allows proteins to retain their three-dimensional structure . 
The Princess Diana.
One of the most honored people is Diana, the Princess of Wales, who was the people's princess and that is how she will remain in our hearts forever. People respect her for the philanthropic work during her life that has helped many people all over the world.
Hundreds of people talked about Diana's kindnesses. She liked ordinary people, though she was rich and had many famous friends. She was always ready to lend a hand. Devoted to the sick and the poor, she visited hospitals for people with AIDS and for lepers and wasn't afraid to touch, to talk to, or to listen to them.
Another reason people admire Diana, is the fact that she worked on charity. Amazingly, Princess Diana was part of forty four charity organizations. Her work with AIDS was global. Once, Princess Diana auctioned seventy nine of her evening gowns and made more than 5 million dollars for ill children. Other charities she advocated for was the eradication of landmines, cancer, and homelessness. And it's not only money that she wanted to give people, but a part of her soul.
People admire this person for her humanitarian work and her kindness. She could understand and sympathize with the people. Princess Diana was a great woman who did great things for the world.