The deprotonated form of the R group of cysteine.
The ratio of protonated to deprotonated form depends on the pKa of the R group and the pH of the solution.
=> Select all the pH values at which the protonated form of the R group would predominate.
9.0
8.3
7.0
11.0
3.0
only pH=3.0 right ?
To determine at which pH values the protonated form of the R group would predominate, we need to consider the pKa of the R group. The pKa is the pH value at which half of the molecules are in the protonated form and half are in the deprotonated form. For cysteine, the pKa of the R group is approximately 8.3.
When the pH is lower than the pKa (pH < pKa), the protonated form predominates. When the pH is higher than the pKa (pH > pKa), the deprotonated form predominates.
Let's evaluate each given pH value to determine whether the protonated form would predominate:
- pH 9.0: pH > pKa (9.0 > 8.3). The deprotonated form would predominate.
- pH 8.3: pH = pKa (8.3 = 8.3). Both forms would be present in equal amounts.
- pH 7.0: pH < pKa (7.0 < 8.3). The protonated form would predominate.
- pH 11.0: pH > pKa (11.0 > 8.3). The deprotonated form would predominate.
- pH 3.0: pH < pKa (3.0 < 8.3). The protonated form would predominate.
So, the pH values at which the protonated form of the R group would predominate are pH 7.0 and pH 3.0.