Are cytosine and Tyrosine the only amino acids that are ionized R-group chains at pH of 7?
To determine whether cytosine and tyrosine are the only amino acids with ionized R-group chains at a pH of 7, we need to analyze the ionization properties of all the amino acids.
Amino acids can be classified based on the ionization states of their R-groups at specific pH levels: acidic, basic, and neutral.
1. Acidic Amino Acids: These amino acids have R-groups that can donate a proton (H+ ion) at a neutral pH of 7. The two common acidic amino acids are aspartic acid (abbreviated as Asp or D) and glutamic acid (abbreviated as Glu or E). Both of these amino acids possess carboxyl groups (COOH), which can ionize to release a proton.
2. Basic Amino Acids: These amino acids have R-groups that can accept a proton (H+ ion) at a neutral pH of 7. There are three basic amino acids: lysine (abbreviated as Lys or K), arginine (abbreviated as Arg or R), and histidine (abbreviated as His or H). These amino acids have amino groups (NH2) within their R-groups that can pick up a proton, thereby becoming positively charged.
3. Neutral Amino Acids: The remaining amino acids have R-groups that do not possess strong acidic or basic properties and remain uncharged at a pH of 7. This category includes cytosine and tyrosine, which have R-groups that are neither acidic nor basic.
Therefore, cytosine and tyrosine are not the only amino acids with ionized R-group chains at a pH of 7. Aspartic acid, glutamic acid, lysine, arginine, and histidine also have ionized R-groups at this pH level. It is important to note that the degree of ionization may vary depending on the specific pKa value of each amino acid's R-group.