8.0: Introduction

Blood, Balance, and Biochemistry: Acid–Base Equilibria in the Body
                            

Figure \(\PageIndex{1}\): A graphic with basic facts about Marie Maynard Daly, the first Black woman to earn a PhD in chemistry in the US. Dr. Daly spent her career researching human biochemistry, leading her to make discoveries ranging from the structure of DNA to the role of cholesterol in human health. Image reproduced with permission from the Archives of the Albert Einstein College of Medicine; Ted Burrows, photographer.

Acid-base reactions are everywhere, from tooth erosion caused by soda to the action of household cleaners to the digestion of food.  These reactions can also influence the behaviour of enzymes, affect the outcome of chemical reactions, and determine whether molecules carry a charge. Understanding how acids and bases behave, how they reach equilibrium, and how they can be controlled is essential to many areas of science and health.

Dr. Marie Maynard Daly, the first Black woman to earn a Ph.D. in chemistry in the United States, made groundbreaking contributions to biochemistry and human physiology. Though she did not study acid–base equilibria directly, much of her research depended on carefully controlling pH to study biological molecules under realistic conditions.

In the 1940s and 1950s, Daly investigated nucleic acids and protein synthesis, uncovering foundational insights into the roles of DNA and RNA. She was the first to show that the four nucleotide bases in DNA, adenine, guanine, thymine, and cytosine, were not present in equal amounts, an observation that laid the groundwork for the discovery of DNA’s structure. She also co-authored one of the earliest studies linking RNA to protein synthesis, which was cited by James Watson in his Nobel Prize address. In all of this work, controlling pH was critical: enzymes function only under the right acid–base conditions, and small shifts can alter how biomolecules behave – even affecting whether they remain in solution or precipitate out of it.

Figure \(\PageIndex{2}\): Depiction of the structure of DNA, highlighting the four different nucleotide bases that Daly mentioned in her work. The phosphate groups (yellow) and deoxyribose sugars (orange) form covalent bonds that make up the "backbone" of DNA. In between them, the four nucleotide bases form hydrogen bonds with each other in specific pairs: adenine (green) with thymine (pink) and guanine (blue) with cytosine (red). Daly used pH to precipitate these nucleotides from solution so that they could be quantified, demonstrating that these four bases could exist in unequal amounts; however, the amounts of adenine and thymine were equal to each other, as were the amounts of guanine and cytosine, indicative of this specific pairing. Image reprinted from Wikimedia Commons with permission under Creative Commons license CC-BY.

Later in her career, Daly shifted her focus to cholesterol and heart disease, and then to creatine metabolism in muscle cells. Across these areas, acid–base chemistry played a supporting but essential role.  Daly needed to control pH to mimic physiological conditions to ensure enzyme function, extract nucleotides and other components from cells, prevent degradation of components, and maintain constant conditions for electrophoresis experiments.

Figure \(\PageIndex{3}\): The relationship between enzyme function and pH. Enzymes operate most efficiently at a specific pH level. This efficiency drops off as the pH moves further and further away from this optimal value. Daly used this principle in her biochemical research to ensure that the enzymes she used or studied were operating optimally.

Acid-base chemistry is not only central to the chemistry curriculum.  It is also vital to our understanding of how the human body functions and how we treat disease. In this chapter, we will examine the same principles Dr. Daly relied on: what defines acids and bases, how to calculate and interpret pH, and the factors affecting acid-base equilibria.

Sources:

1. Allfrey, V.; Daly, M. M.; Mirsky, A. E. SYNTHESIS OF PROTEIN IN THE PANCREAS II. THE ROLE OF R/BONUCLEOPROTEIN IN PROTEIN SYNTHESIS. Journal of General Physiology 1953, 37 (2), 157–175.
2. Daly, M. M.; Allfrey, V. G.; Mirsky, A. E. PURINE AND PYRIMIDINE CONTENTS OF SOME DESOXYPENTOSE NUCLEIC ACIDS. Journal of General Physiology 1950, 33 (5), 497–510. https://doi.org/10.1085/jgp.33.5.497.
3. Kaplan, J. Marie Maynard Daly. Science History Institute. https://www.sciencehistory.org/education/scientific-biographies/marie-maynard-daly/ (accessed 2025-07-31).
4. Watson, J. James Watson - Nobel Lecture, 1962. https://www.nobelprize.org/prizes/medicine/1962/watson/lecture/.
5. Marie Maynard Daly - American Chemical Society. https://www.acs.org/education/whatischemistry/landmarks/daly.html (accessed 2025-07-31).
6. Marie Maynard Daly | Science - UNSW Sydney. UNSW Sites. https://www.unsw.edu.au/science/about-us/equity-diversity-inclusion/science-history-trail/marie-maynard-daly (accessed 2025-07-31).