Skip to main content
Biology LibreTexts

4: Buffers, Polyprotic acids; Amphoteric Substances,

Reading & Problems: LNC p. 63-66, p. 72 prob. 12, 15-18, 20-29; Segel p. 92 prob. 25 a,d,f (note: pKa for ammonia is 9.26), 32, 34, 38a (here is the external link: solution to 38a, but see if you can do it yourself first!), p. 93 prob. 40, 42 (if additional clarification is needed, read Segel p. 31- 41, 53-62)

I. Buffers - mixtures of conjugate acid and conjugate base at ±1 pH unit from pH = pKa. Resistant to changes in pH in response to small additions of H+ or OH-.

II. Polyprotic acids - dissociation of each H+ can be treated separately if the pKa values are different.

III. Amphoteric substances - can act as both acids and bases.

IV. Introduction to proteins - linear chains of amino acids connected by peptide bonds.

  1. Enzymes - protein catalysts, facilitate/enable most of the reactions in a cell.
  2. Binding - receptors mediate communication, O2 storage and transport (myoglobin, hemoglobin), antibodies for defense.
  3. Channels/pumps - proteins embed in cell membranes allow selective flow or transport of small molecules.
  4. Structure - collagen in connective tissue of animals, extensin in plant cell walls.
  5. Movement - dynamic assembly of cytoskeleton (actin filaments, microtubules), motor proteins provide directional movement of cells and subcellular components.

V. external link: alpha amino acids - 20 different ones are used in protein synthesis. The properties page also links to external link: 3-D structure views.


Some additional take home information

Lecture 4 info.jpg