Question

Which of the following is true regarding a fatty acid molecule in water?

1) It is positively charged at physiological pH, but can become neutral when the pH is high enough.
2) It is positively charged at physiological pH, but can become neutral when the pH is low enough.
3) It is negatively charged at physiological pH, but can become neutral when the pH is high enough.
4) It is negatively charged at physiological pH, but can become neutral when the pH is low enough.
5) It is not charged at physiological pH.

Answer 1

Fatty acid molecules are typically uncharged at physiological pH but can become negatively charged when the pH is high enough due to the deprotonation of the carboxyl group.

Step-by-step explanation:

The correct answer to the question regarding the charge of a fatty acid molecule at physiological pH is that it is typically uncharged. However, fatty acids can obtain a negative charge if the pH is sufficiently high. At physiological pH, which is generally around 7.4, the carboxyl group (-COOH) of a fatty acid is typically in its protonated form and does not carry a charge. If the pH rises to a level where the carboxyl group loses a proton, the fatty acid becomes negatively charged (-COO-). This principle relates to the behavior of amphipathic molecules like phospholipids, which have both hydrophobic (fatty acid tails) and hydrophilic (phosphate group head) components. The phosphate head can be negatively charged, but this is a separate aspect of the molecule distinct from the fatty acid portion.