pKa of the amino group of glycine is 9.6. The pH range at which glycine can be used as an effective buffer due to its amino group is:

Appeared in: HP CHO -9 October 2022

Explanation

A buffer solution is most effective at resisting pH changes when the pH is close to the pKa of the weak acid or base.
The generally accepted effective buffering range is defined as pKa ± 1 pH unit.
Given the pKa of glycine's amino group is 9.6, the effective range is calculated as 9.6 ± 1.
This results in a lower limit of 8.6 (9.6 - 1) and an upper limit of 10.6 (9.6 + 1).
Therefore, glycine can act as an effective buffer due to its amino group in the pH range of 8.6 to 10.6.

Option A: This range (7.6 to 9.6) is centered at 8.6, which is 1 pH unit below the pKa. It only covers the lower half of the effective buffering zone and is not centered on the pKa.
Option C: This range (9.6 to 11.6) is centered at 10.6, which is 1 pH unit above the pKa. It only covers the upper half of the effective buffering zone and is not centered on the pKa.
Option D: This range (10.6 to 12.6) is centered at 11.6. This is 2 pH units away from the pKa of 9.6, placing it well outside the effective buffering capacity of glycine's amino group.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Buffering range of amino acids as background academic context rather than a clinical decision trigger.
Understanding buffer systems is crucial in nursing as the human body relies on them to maintain homeostasis. The bicarbonate buffer system in the blood is a prime example, keeping pH between 7.35 and 7.45.
Proteins, which are made of amino acids like glycine, act as significant physiological buffers due to their ionizable side chains, helping to absorb excess acid or base.
What if? If a patient develops metabolic acidosis, the blood pH drops below 7.35. The body's buffer systems, including proteins and bicarbonate, will be working to neutralize the excess acid. A nurse would monitor arterial blood gases (ABGs) to assess the severity and the body's compensation.

How to Approach the Question

First, identify the core concept being tested, which is the definition of an 'effective buffer range'.
Recall the key principle: A buffer is most effective within a range of pKa ± 1 pH unit.
Identify the given pKa value from the question stem, which is 9.6 for the amino group of glycine.
Apply the principle by performing the calculation: 9.6 - 1 = 8.6 and 9.6 + 1 = 10.6.
Determine the resulting range, which is 8.6 to 10.6.
Compare this calculated range with the given options and select the one that matches.

Concept Tested & Keywords

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E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 2 — Subpart A (pp 1-239 of 478) p. 71-73

E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 1 (pp 26-370 of 370) p. 97-99

Practise the full HP CHO -9 October 2022

Attempt every question from this paper in a timed mock, then review the full solution for each one.