International Board of Certified Lactation Consultant (IBCLC) Practice Exam

Which of the following is an example of a low molecular weight substance?

1. Caffeine

2. Insulin

3. Albumin

4. Chloramphenicol

The correct answer is: Caffeine

Caffeine is indeed an example of a low molecular weight substance. Low molecular weight compounds are typically defined as those with a molecular weight of less than about 500 daltons. Caffeine has a molecular weight of approximately 194 daltons, making it well below this threshold. In contrast, insulin is a peptide hormone that has a significantly higher molecular weight due to its structure, which consists of 51 amino acids. Albumin is a protein found in blood plasma and has an even higher molecular weight, while chloramphenicol, an antibiotic, also has a molecular weight that would categorize it as a larger compound compared to caffeine. Understanding the categorization based on molecular weight is important in various fields, including pharmacology and biochemistry, as it often affects how substances are absorbed, distributed, metabolized, and eliminated in the body.