Facilitated diffusion

Definition

Facilitated diffusion is a process by which molecules move across a cell membrane through specific protein channels or carriers without the expenditure of energy. This transport mechanism is crucial for the movement of polar or charged substances that cannot easily pass through the lipid bilayer, allowing them to enter or exit the cell efficiently. Facilitated diffusion relies on concentration gradients, ensuring that molecules move from areas of higher concentration to areas of lower concentration.

5 Must Know Facts For Your Next Test

1. Facilitated diffusion does not require energy input because it relies on the natural movement of molecules down their concentration gradient.
2. There are two main types of proteins involved in facilitated diffusion: channel proteins and carrier proteins, each serving different functions in transport.
3. Facilitated diffusion is selective; only specific molecules can pass through the protein channels or carriers based on their size, charge, and shape.
4. This process is vital for cells to acquire essential nutrients like glucose and amino acids while maintaining homeostasis.
5. Facilitated diffusion can be influenced by factors such as temperature, pH, and the availability of carrier proteins or channels.

Review Questions

• How do channel proteins and carrier proteins differ in their roles in facilitated diffusion?
  • Channel proteins form open pathways that allow specific ions or small molecules to flow directly through the membrane when they are available. In contrast, carrier proteins bind to the target molecule, undergo a conformational change, and then release the molecule on the other side of the membrane. This distinction is important because channel proteins provide continuous passage for ions, while carrier proteins are more selective and can transport larger or more complex molecules.
• What factors can affect the rate of facilitated diffusion across a cell membrane?
  • Several factors can influence how quickly facilitated diffusion occurs. These include the concentration gradient—the greater the difference in concentration, the faster the rate—temperature, which affects kinetic energy and movement speed, and the number of available channel or carrier proteins. If all channels are occupied, transport will slow down even if a high concentration gradient exists. Thus, both environmental conditions and molecular characteristics play key roles.
• Evaluate the importance of facilitated diffusion in maintaining cellular homeostasis and how disruptions could impact cell function.
  • Facilitated diffusion is essential for maintaining cellular homeostasis by regulating nutrient uptake and waste removal. For example, glucose needs to enter cells rapidly for energy production; disruptions in this process could lead to insufficient energy levels, affecting overall cell function and viability. Additionally, if ion balance is compromised due to faulty channel proteins, it could lead to cellular dysfunctions like altered signaling pathways or impaired muscle contractions. Therefore, proper functioning of facilitated diffusion mechanisms is critical for cellular health.

Related terms

Channel proteins: Proteins that create a passageway in the cell membrane for specific ions or molecules to pass through, aiding in facilitated diffusion.

Carrier proteins: Proteins that bind to specific molecules and change shape to shuttle them across the membrane, also playing a key role in facilitated diffusion.

Concentration gradient:

The difference in concentration of a substance across a space, driving the movement of molecules during facilitated diffusion.