pH and Buffers Bonnie Ownley Department of Entomology and Plant Pathology The University of Tennessee, Knoxville

What is pH? Measure of the concentration of hydrogen ions (H + ) in a solution

Why is pH important? All living things on earth are water-based systems, and are very dependent on acid-base equilibrium. The cell environment is always buffered at pH 7.0.

The pH scale ranges from 0 (extremely acid) to 14 (extremely basic). Acidic conditions = 0 to 6.9. Alkaline conditions = 7.1 to 14.0 The pH scale is logarithmic, so that for each 1 unit change in pH, there is actually a ten-fold change in acidity or alkalinity.

How does this relate to proteins? In biology, macromolecules, such as proteins, act as acids and bases by accepting and donating protons. Enzymes (proteins) require a certain pH level for activity.

Enzymes are large molecules and have acidic and basic groups, rather than just being an acid or a base. Hydrophobic Hydrophilic Basic Acidic

On protein (enzyme) molecules, changes in pH determine which groups are protonated (have an attached hydrogen ion). Enzyme At low pH (acidic conditions), the -NH 3 + group will not be affected, but the -COO - will pick up a hydrogen ion. In this case, we have lost the ability to form ionic bonds between the substrate and the enzyme. If those bonds were needed to attach the substrate and activate it, then at a lower pH, the enzyme will not work. If pH is higher than 7 (alkaline conditions), the - COO - group will not be affected, but the -NH 3 + group will lose a hydrogen ion.

What is a buffer? Usually a weak organic acid and its salt Acts to protect against abrupt changes in acidity or alkalinity

Buffer for Exercise Phosphate buffered saline Components: NaCl (sodium chloride) KCl (potassium chloride) KH 2 PO 4 (monopotassium phosphate) Na 2 HPO 4 ×7H 2 O (disodium phosphate)