The document discusses the role of buffers in maintaining pH levels in biological systems, emphasizing that even small pH changes can significantly impact biological processes. It defines buffer systems as mixtures of weak acids and their conjugate bases that resist pH changes and introduces the Henderson-Hasselbalch equation for calculating pKa, pH, and molar ratios of proton donors and acceptors. Additionally, it highlights two key biological buffers: the phosphate buffer system in the cytoplasm and the bicarbonate system in blood plasma.

1. Buffers

2. Buffering against pH Changes
in Biological Systems
• Almost every biological process is pH
dependent
• a small change in pH produces a large change
in the rate of the process.
• Cells and organisms maintain a specific and
constant cytosolic pH, keeping biomolecules
in their optimal ionic state, usually near pH 7

3. Constancy of pH is achieved primarily by
biological buffers
Buffers Are Mixtures of Weak Acids and
Their Conjugate Bases

4. Definition of a buffer system
• Buffers are aqueous systems that tend to
resist changes in pH when small amounts of
acid (H) or base (OH) are added.
• A buffer system consists of a weak acid (the
proton donor) and its conjugate base (the
proton acceptor).

5. The acetic acid–acetate pair as a buffer
system

6. The Handerson Hasselbalch
equation

9. • The Henderson-Hasselbalch equation also
allows us to
(1)calculate pKa, given pH and the molar ratio of
proton donor and acceptor
(2) Calculate pH, given pKa and the molar ratio
of proton donor and acceptor
(3) calculate the molar ratio of proton donor
and acceptor, given pH and pKa.

11. Biological buffers
• Two especially important biological buffers
are the phosphate and bicarbonate systems
• The phosphate buffer system, which acts in
the cytoplasm of all cells, consists of H2PO4 as
proton donor and HPO4
2-
as proton acceptor

12. • Blood plasma is buffered in part by the
bicarbonate system, consisting of carbonic
acid (H2CO3) as proton donor and bicarbonate
(HCO3) as proton acceptor: