The textbook is giving you a simplified version of the overall reaction, without considering the actual mechanism of how the reaction occurs.  The actual reaction is between an amino acid linked to transfer RNA (tRNA) which serves as an activated carrier of the amino acid, and allows for the polymerization to take place in a regulated and "programmed" way. Since the protein  sequence is ultimately determined by a specific DNA sequence, there is a series of steps involved to ensure the synthesis of a specific structure. A more advanced biochemistry textbook should describe the multi-step process of translating a DNA sequence into a protein.

Thanks Greg.

To quote the textbook "At physiological pH, the reaction shown here does not occur to any appreciable extent". I think the quest to simplicity has taken a step to far this time...

Yoram

Of course ribosomes do special chemistry. Even in the chemistry we conduct in glassware, the carboxylic group has to be first "activated" by converting the hydroxyl of the carboxy group into some kind of "good leaving group", and only then the activated carboxylic species is allowed to react with the amino group, under specially designed conditions facilitating the substitution of the leaving group with the amine of AA2. Proteins do the same trick, in their own way (as Greg Cote suggested). I guess, it is safe to assume that fundamental scientific questions, like your original one, would not stay unanswered for so long...