Biochemistry

To address the question regarding which group does not contain amino acids with ionizable side chains, let's first understand the nature of amino acid side chains and how they relate to the groups mentioned. Amino acids are the building blocks of proteins and are characterized by a central carbon atom (the alpha carbon), an amino group, a carboxyl group, and a distinctive side chain (R-group). The properties of the side chain determine the overall properties of the amino acid, including whether it is hydrophobic, polar, and whether it can ionize. 1. **Negatively-charged amino acids**: These amino acids have side chains that can lose a proton and carry a negative charge at physiological pH (around 7.4). Examples include aspartic acid (Asp, D) and glutamic acid (Glu, E). Their side chains contain a carboxyl group that can ionize, so they do have ionizable side chains. 2. **Positively-charged amino acids**: These amino acids have side chains that can gain a proton and carry a positive charge at physiological pH. Examples include lysine (Lys, K), arginine (Arg, R), and histidine (His, H). Their side chains contain an amino group (in the case of lysine and arginine) or an imidazole ring (in the case of histidine) that can ionize, so they also have ionizable side chains. 3. **Hydrophobic amino acids**: These amino acids have side chains that are generally nonpolar and do not interact favorably with water. Examples include leucine (Leu, L), isoleucine (Ile, I), and valine (Val, V). Their side chains are made up of carbon and hydrogen atoms and do not ionize under physiological conditions. Therefore, hydrophobic amino acids do not have ionizable side chains. 4. **Polar amino acids**: These amino acids have side chains that are polar but not charged at physiological pH. Examples include serine (Ser, S), threonine (Thr, T), and tyrosine (Tyr, Y). Some polar amino acids, like tyrosine, can ionize under certain conditions (e.g., tyrosine can lose a proton from its phenolic hydroxyl group at high pH), but not all polar amino acids have ionizable side chains. From the information provided, we can conclude that all groups except "Hydrophobic amino acids" contain amino acids with ionizable side chains. Hydrophobic amino acids have side chains that are nonpolar and do not ionize at physiological pH, making them the correct answer to the question.

Math

Amino acids with ionizable side chains are found in all groups except: - Negatively-charged amino acids - Positively-charged amino acids - Hydrophobic amino acids - Polar amino acids

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