Why do amino acids exist as Zwitterions at physiological pH?

Related questions

1. What is the difference between an amino acid and an amino acid residue?
2. What affects pKa of amino acids?
3. How do you identify amino acids?
4. How does pH affect the amino acid side chains of a protein?
5. What happens to amino acids at high pH?
6. What are some reactions that amino acids undergo?
7. What is amino acid sequence?
8. Does a weak acid have a high or low pKa?
9. What is the pH of amino acids?
10. Which amino acids are acidic and basic?

Tags

1. #charged
2. #positively
3. #zwitterions
4. #exist
5. #value
6. #molecules
7. #group
8. #certain
9. #zwitterion
10. #added
11. #hydrogen
12. #ability
13. #because
14. #containing
15. #amino
16. #carboxylate
17. #nearly
18. #solution
19. #captures
20. #different
21. #becomes