Molecular weight

Definition

Molecular weight is the mass of a molecule, usually expressed in daltons (Da) or grams per mole (g/mol), calculated as the sum of the atomic weights of all atoms in a molecule. This measurement is critical as it influences how substances are absorbed and distributed in biological systems. Understanding molecular weight helps in predicting the behavior of chemicals in living organisms, including their solubility, permeability, and interaction with biological membranes.

5 Must Know Facts For Your Next Test

1. Molecules with lower molecular weights generally have higher rates of absorption through biological membranes compared to those with higher molecular weights.
2. The molecular weight can affect the distribution of substances within the body, as larger molecules may be restricted from passing through certain barriers such as cell membranes.
3. In pharmacology, understanding the molecular weight is essential for dosage calculations and to ensure proper drug delivery and efficacy.
4. Molecular weight also plays a role in the metabolism of substances; compounds may be metabolized differently based on their size and structure.
5. For toxicants, high molecular weight substances might accumulate in tissues due to their limited ability to be absorbed or excreted effectively.

Review Questions

• How does molecular weight influence the absorption rate of drugs in the body?
  • Molecular weight significantly impacts how quickly and effectively drugs are absorbed into the bloodstream. Generally, smaller molecules tend to be absorbed more rapidly because they can easily pass through biological membranes, such as cell walls. In contrast, larger molecules may face barriers that slow down their absorption, leading to variations in therapeutic effects and bioavailability.
• Discuss the implications of molecular weight on the distribution of toxicants within an organism.
  • The molecular weight of toxicants has important implications for their distribution within an organism. Higher molecular weight compounds may struggle to pass through cellular membranes, which can result in them accumulating in specific tissues. This accumulation can enhance toxicity in certain organs while limiting exposure elsewhere, necessitating careful consideration when assessing risks associated with different toxicants.
• Evaluate how understanding molecular weight can help predict the behavior of new chemical entities in drug development.
  • In drug development, evaluating the molecular weight of new chemical entities allows researchers to predict their absorption, distribution, metabolism, and excretion (ADME) profiles. By analyzing how molecular weight affects these factors, developers can optimize chemical structures for improved bioavailability and efficacy. Moreover, this knowledge helps tailor dosing regimens and assess potential toxicity, ultimately leading to safer and more effective therapeutic agents.

Related terms

Molarity: A measure of concentration representing the number of moles of a solute per liter of solution, important for understanding how drugs and toxins interact in a solution.

Bioavailability:

The fraction of an administered dose of a substance that reaches systemic circulation, which can be influenced by its molecular weight and absorption characteristics.

Partition Coefficient: A ratio that describes how a substance divides between two immiscible solvents, often used to predict distribution in biological systems based on molecular weight and polarity.