( ( In ( ( the formation ) ( of proteins ) ) ) ( , ( it ( ( is ( ( a ( condensation reaction ) ) ( that ( ( links ( ( the ( amino group ) ) ( of ( one ( amino acid ) ) ) ) ) ( to ( ( the ( variable ( side chain ) ) ) ( of ( the ( adjacent ( amino acid ) ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN In) (NP (NP (DT the) (NN formation)) (PP (IN of) (NP (NNS proteins))))) (, ,) (NP (PRP it)) (VP (VBZ is) (NP (NP (DT a) (NN condensation) (NN reaction)) (SBAR (WHNP (WDT that)) (S (VP (VBZ links) (NP (NP (DT the) (JJ amino) (NN group)) (PP (IN of) (NP (CD one) (JJ amino) (NN acid)))) (PP (TO to) (NP (NP (DT the) (JJ variable) (NN side) (NN chain)) (PP (IN of) (NP (DT the) (JJ adjacent) (JJ amino) (NN acid)))))))))) (. .)))
In the formation of proteins, it  is a condensation reaction that links the amino group of one amino acid to the variable side chain of the adjacent amino acid.
(ROOT (S (NP (JJ Many) (NNS enzymes)) (VP (VBP are) (NP (NP (JJ simple) (NNS proteins)) (VP (VBG consisting) (ADVP (RB entirely)) (PP (IN of) (NP (QP (CD one) (CC or) (JJR more)) (JJ amino) (NN acid) (NNS chains)))))) (. .)))