[crays]

Thanks, i understand now.

[rahul2ghosh]

Hi Guys.. 

I am a new member and was not aware that such a site exists. I was a science student and finished my schooling way back. My Job however took me away from science (esp. chemistry). So when I saw this site.. could not control myself from from relearning the old concepts...!

Hey Crays! .. though others have aptly explained the concept and you have acknowledged them too, please let me explain a little more.. and all please correct me where I am wrong... thus I can also relearn with Crays... 

As per the structure of glycine:   H2NCH2COOH
... Amine group :NH2- being basic wants to capture one Proton (H+) while Carboxylic group -COOH being acidic wants to donate one Proton, so that they can form the Zwitter Ion.

Now all this depends on the pH of the solution. If the pH < 7, then the solution is acidic (excess Protons) and thus glycine exists as a positive ionH3N(+)CH2COOH. For pH > 7 the solution is basic (excess Hydroxide Ions), thus glycine exists as a negetive ion H2NCH2COO(-). However, for every Amino Acid there is a specific range of pH where it behaves as if it a neutral species! This is when glycine exists as a zwitter ion.

You may think why I am refering a zwitter ion as neutral species 

... because zwitter ion has equal positve charge and negetive charge, thus the net glycine stucture is Neutral. The pH at which this zwitter ion exists is called Isoelectric Point.

Hope... I still remember few concepts correctly