Muscle cells deficient in oxygen reduce pyruvate (an...

Muscle cells deficient in oxygen reduce pyruvate (an intermediate in metabolism) to lactate at a cellular pH of approximately 7.4 . (a) Why do we say pyruvate and lactate, rather than pyruvic acid and lactic acid? (b) Alter the above structures to create pyruvic acid and lactic acid. (c) Show hydrogen bonding of water to both pyruvate and lactate. Would you expect a difference in water solubility of lactate and pyruvate? Explain.

Muscle cells deficient in oxygen reduce pyruvate (an intermediate in metabolism) to lactate at a cellular pH of approximately 7.4 .
(a) Why do we say pyruvate and lactate, rather than pyruvic acid and lactic acid?
(b) Alter the above structures to create pyruvic acid and lactic acid.
(c) Show hydrogen bonding of water to both pyruvate and lactate. Would you expect a difference in water solubility of lactate and pyruvate? Explain.

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Key Concepts

Acid?Base Equilibrium at Physiological pH

At physiological pH (around 7.4), weak acids such as pyruvic acid and lactic acid are predominantly deprotonated, existing as their conjugate bases (pyruvate and lactate, respectively). This concept explains why they are referred to by their anionic forms rather than as neutral acids in biological contexts.

Conjugate Base and Acid Structural Representation

Structural notation distinguishes between the protonated and deprotonated forms of a molecule. The conversion of a carboxylic acid into its conjugate base involves the loss of a hydrogen ion from the acidic group, resulting in a change in the molecule’s charge and structure. This concept is important for understanding how the same molecule can be represented differently depending on the pH of the medium.

Hydrogen Bonding and Water Solubility

Hydrogen bonding plays a key role in determining a molecule's solubility in water. Molecules with groups capable of participating in hydrogen bonds (such as the carboxylate and hydroxyl groups present in lactate and pyruvate) tend to be more water-soluble. Subtle differences in molecular structure, including the presence or absence of an acidic proton, can influence the pattern and strength of hydrogen bonding interactions, thereby affecting overall solubility.

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