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How many distinct pKa values would you expect for the amino acid aspartic acid?
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3. Amino Acids
Amino Acid Groups
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Which of the following amino acids would be positively charged at physiological pH (approximately 7.4)?
A
Serine
B
Aspartic acid
C
Lysine
D
Glutamine
Guida verificata passo dopo passo1
Step 1: Understand the concept of physiological pH. Physiological pH is approximately 7.4, which is slightly basic. Amino acids can exist in different ionization states depending on the pH of their environment.
Step 2: Recall the properties of amino acid side chains. Amino acids with basic side chains, such as lysine, arginine, and histidine, tend to be positively charged at physiological pH due to the protonation of their side groups.
Step 3: Analyze the amino acids provided in the question. Serine has a hydroxyl (-OH) group, which is neutral at physiological pH. Aspartic acid has a carboxyl (-COOH) group in its side chain, which is negatively charged at physiological pH. Glutamine has an amide (-CONH2) group, which is neutral at physiological pH.
Step 4: Focus on lysine. Lysine has an amino (-NH3+) group in its side chain, which remains protonated and positively charged at physiological pH. This makes lysine the correct answer.
Step 5: Conclude that lysine is positively charged at physiological pH due to the protonation of its basic side chain, while the other amino acids listed are either neutral or negatively charged at this pH.
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