At pH 7.2, what charge will a lysine side chain typically carry?

At pH 7.2, what charge will a lysine side chain typically carry?

• A. Neutral
• B. Positive
• C. Negative
• D. Variable

Answer: (B)

At pH 7.2, a lysine side chain typically carries a positive charge. Lysine is an amino acid with a side chain that contains an amino group (-NH2) that can accept a proton (H+). In biological systems, especially at physiological pH levels, this amino group is protonated, forming a positively charged ammonium ion (-NH3+). The pKa of the side chain amino group of lysine is about 10.5, meaning that at pH values below its pKa, the amino group will be predominantly protonated and positively charged. Since pH 7.2 is well below the pKa of the lysine side chain, we can confidently conclude that the lysine side chain will predominantly exist in its protonated, positively charged form at this pH. Other options, such as neutral or negative charges, do not accurately reflect the state of the lysine side chain at this pH. A neutral charge would imply that the amino group is not protonated, which contradicts the conditions near physiological pH. A negative charge is not typical for lysine's side chain at this pH, as the side chain does not have functional groups that would be deprotonated under

At pH 7.2, a lysine side chain typically carries a positive charge. Lysine is an amino acid with a side chain that contains an amino group (-NH2) that can accept a proton (H+). In biological systems, especially at physiological pH levels, this amino group is protonated, forming a positively charged ammonium ion (-NH3+).

The pKa of the side chain amino group of lysine is about 10.5, meaning that at pH values below its pKa, the amino group will be predominantly protonated and positively charged. Since pH 7.2 is well below the pKa of the lysine side chain, we can confidently conclude that the lysine side chain will predominantly exist in its protonated, positively charged form at this pH.

Other options, such as neutral or negative charges, do not accurately reflect the state of the lysine side chain at this pH. A neutral charge would imply that the amino group is not protonated, which contradicts the conditions near physiological pH. A negative charge is not typical for lysine's side chain at this pH, as the side chain does not have functional groups that would be deprotonated under