Facilitated diffusion

Definition

Facilitated diffusion is a process that allows substances to cross biological membranes with the assistance of special proteins called transporters, without the need for energy input. This mechanism is vital in the movement of polar or charged molecules across cell membranes, which are otherwise impermeable to these substances, and plays a key role in drug distribution, cellular uptake, and transdermal drug delivery.

5 Must Know Facts For Your Next Test

1. Facilitated diffusion is specific to the type of substance being transported; each transporter protein typically accommodates only particular molecules or ions.
2. This process occurs down the concentration gradient, meaning substances move from an area of higher concentration to an area of lower concentration.
3. Facilitated diffusion does not require ATP; instead, it relies on the natural kinetic energy of molecules and the action of transport proteins.
4. Transdermal drug delivery systems often utilize facilitated diffusion to ensure that drugs penetrate the skin barrier effectively, providing a steady release into the bloodstream.
5. Factors such as temperature, pH, and membrane fluidity can influence the rate of facilitated diffusion, affecting how quickly substances can move across cell membranes.

Review Questions

• How does facilitated diffusion differ from simple diffusion in terms of mechanism and protein involvement?
  • Facilitated diffusion differs from simple diffusion in that it requires specific transport proteins to help move substances across cell membranes. While simple diffusion allows small nonpolar molecules to pass directly through the lipid bilayer without assistance, facilitated diffusion is necessary for polar or charged molecules that cannot easily cross the hydrophobic core of the membrane. The presence of transport proteins ensures that these larger or charged molecules can move efficiently down their concentration gradient.
• Discuss how facilitated diffusion contributes to effective transdermal drug delivery and what factors may impact its efficiency.
  • Facilitated diffusion is essential in transdermal drug delivery as it helps drugs penetrate the skin's barrier effectively. This process allows for a controlled release of drugs into the bloodstream without needing needles or invasive methods. Factors impacting its efficiency include the characteristics of the drug itself (such as molecular size and polarity), formulation components like penetration enhancers, and physiological factors like skin thickness and hydration levels.
• Evaluate the importance of facilitated diffusion in cellular processes and how alterations in transporter function could impact drug therapies.
  • Facilitated diffusion is critical for various cellular processes including nutrient uptake, waste removal, and signal transduction. If transporter proteins malfunction or are altered due to genetic mutations or disease states, this can lead to impaired cellular function and affect how cells respond to drug therapies. For instance, if a transporter for a certain medication becomes less effective, it could result in suboptimal therapeutic levels, necessitating adjustments in dosage or alternative treatment strategies to achieve desired outcomes.

Related terms

Transport proteins: Proteins that help facilitate the movement of substances across cell membranes, including channels and carriers that assist in facilitated diffusion.

Passive transport: The movement of substances across a membrane without the use of energy, which includes facilitated diffusion as well as simple diffusion.

Permeability:

The property of a membrane that determines how easily substances can pass through it, influenced by factors such as size, charge, and the presence of specific transporters.