What Is Facilitated Diffusion?
Facilitated diffusion is the process of spontaneous passive transport of molecules or ions across a biological membrane via specific transmembrane integral proteins. Like simple diffusion, it does not require chemical energy from ATP. It is used for substances that cannot cross the lipid bilayer directly due to their size, charge, or polarity.
Section 2: Key Components
This process relies on two main types of transport proteins: channel proteins and carrier proteins. Channel proteins form a pore or channel through the membrane, allowing specific ions to pass through quickly. Carrier proteins bind to a specific molecule, change their shape, and then release the molecule on the other side of the membrane. Both types are highly specific to the substance they transport.
Section 3: A Practical Example
A classic example of facilitated diffusion is the transport of glucose into most body cells. Glucose is too large and polar to diffuse across the cell membrane on its own. Instead, it binds to a specific carrier protein called a glucose transporter (GLUT). The protein then changes shape and moves the glucose molecule into the cell, down its concentration gradient.
Section 4: Importance in Biological Systems
Facilitated diffusion is crucial for the survival of cells. It allows for the rapid uptake of essential nutrients like glucose and amino acids, which are needed for metabolism and growth. It also enables the transport of ions, which is vital for nerve impulse transmission and maintaining cellular homeostasis, all without expending the cell's valuable energy resources.