29. Which of the following statements about peptidoglycan is incorrect? (A) It is the main component of bacterial cell wall, which helps bacteria maintain a certain shape and resist hypotonic environments. (B) The polysaccharide chain of peptidoglycan is aβ(1-4) linked copolymer of N- acetylglucosamine and N-acetylmuramic acid. (C) The polysaccharide chains of peptidoglycan are cross-linked together through tetrapeptides. (D) One end of the tetrapeptide chain links to a N-acetylglucosamine in the polysaccharide chain at the C-2 position. (E) In many Gram negative bacteria, two adjacent tetrapeptide chains are joined directly between the e-amino group of lysine in one chain and the carboxyl group of D-alanine in the other.