BIOLOGY
AMINO ACIDS
|
Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
|
|
|
Histidine
|
|
|
Arginine
|
|
|
Cysteine
|
|
|
Serine
|
Detailed explanation-1: -Of the basic amino acid side chains, histidine has the lowest pKa (around 6) and is therefore neutral at around physiological pH.
Detailed explanation-2: -other amino acids which have ionizable side chains. These include arginine, aspartic acid, cysteine, glutamic acid, histidine, lysine and tyrosine.
Detailed explanation-3: -The pkA values of glutamic acid and aspartic acid are 4.1, the pKa of cysteine is 6.0, the pKa value of lysine is 8.3, the pKa value of lysine is 10.8, the pKa value of tyrosine is 10.9 and the pKa value of arginine is 12.5.
Detailed explanation-4: -The pKa of histidine is sensitive to its specific chemical environment; for example, it has been found that the pKa values of the histidine residues in the protein phosphatidylinositol-specific phospholipase C vary between 5.4-7.6 as determined by 1H NMR spectroscopy [31].