Try not to get too bogged down with the amino acid classifications. In general, this may be beyond the scope of the MCAT¨. If you take anything away from this chapter, focus on amino acid structure and reactions (above) with less emphasis on classification (below).
In fact, this section might help you out more for a biochem exam or in medical school.
Amino acid characteristics are numerous, so if you want to be super hard core, you can memorize this jingle that is sung to the tune of the Beverly Hillbillies theme54.1:
| Come an' listen to my story about the a-mi-nos |
| Five Al-i-phats kick off our show |
| Glycine, Alanine, Valine and then |
| Leucine and Iso make up half of ten |
| Well the next thing you know are three aromats |
| phenylalanine (F) is right off the bat |
| tYrosine has alcohol next to its ring |
| And tryptophan (W) has indole double ring thing. |
| Sulfur in Cysteine; it loves to bond |
| Sulfur Methionine is much more a snob |
| Alcoholic Serine, well wouldn't you know, |
| And Threonine's OH gives a warm glow. |
| Acid-aspartic (D) and glutamic (E) are ionized |
| With pK of 4, their protons are lysed, |
| asparagine (N) and glutamine (Q) play a different role |
| With amides they're neutral but they both have poles |
| lysine(K) and aRginine are the basic kind, |
| But Histidine's imidazole can't make up its mind, |
| Proline, the last one, coming at the end |
| It's imine, an oddball, proteins use to bend. |
Classification by pH: basic and acidic amino acids:
| Histidine | Glutamic acid |
|---|---|
| Arginine | Aspartic acids |
| Lysine |
Classification by essential amino acids for humans:
| Phenylalanine | Thronine | Histidine |
|---|---|---|
| Valine | Isoleucine | Arginine |
| Tryptophan | Methionine | Leucine |
| Lysine |