"He is liar"
Histidine. Lysine. Arginine.
Updated on 22/11/2013:
Question asked on tumblr:
Basicity: the willingness to donate electrons
Wait, why would they be positive again? Aaaaahhhh
Hey don’t get confused between your “basic” concepts! *pun intended*
I was talking about being positive in the physiological pKa.
All amino acids can act as either an acid or a base because they have a carboxyl group than can lose protons and an amino group than can gain protons/donate electrons.
Amino acids that are said to be basic have an extra moiety which will accept electrons (Their side chains contain nitrogen and resemble ammonia, which is a base at neutral pH).
They will have iso electric points at a pH higher than physiological pH and will be positively charged at physiological pH (You need a more alkaline environment to obtain an overall neutral charge because the amino group can hold onto another proton).
In other words, their pKa’s are high enough that they tend to bind protons, gaining a positive charge in the process.
Similarly, amino acids that are said to be acidic have an extra carboxyl group. They will have iso electric points at a pH lower than physiological pH and be negatively charged at physiological pH (You need a more acidic environment to obtain an overall neutral charge because the carboxyl groups can more easily lose a proton).