Diffusion and Membrane Transport
Diffusion is a fundamental process in biology that involves the movement of molecules from areas of high concentration to low concentration. This page explores two types of diffusion: simple diffusion and facilitated diffusion.
Simple diffusion, also known as lipid diffusion, occurs when molecules can pass directly through the cell membrane without the assistance of transport proteins. This process is generally faster than facilitated diffusion.
Example: Oxygen and carbon dioxide can diffuse directly through the lipid bilayer of cell membranes.
Facilitated diffusion involves the use of carrier proteins and protein channels to help specific molecules cross the cell membrane. This process is slower than simple diffusion but allows for the transport of molecules that cannot easily pass through the lipid bilayer on their own.
Vocabulary: Carrier proteins are membrane proteins that bind to specific molecules and undergo conformational changes to transport them across the membrane.
Both simple and facilitated diffusion are passive processes, meaning they rely on the kinetic energy of the diffusing molecules and do not require external energy input such as ATP.
Highlight: The rate of diffusion is described by Fick's Law, which states that the rate is proportional to the concentration difference and surface area, and inversely proportional to the diffusion distance.
The page also illustrates different types of membrane proteins involved in facilitated diffusion:
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Channel proteins: These form water-filled hydrophilic pores that allow specific water-soluble ions to pass through. They can be non-gated or gated channels.
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Carrier proteins: These have specific binding sites for molecules. When a molecule binds, the protein undergoes a conformational change, releasing the molecule on the other side of the membrane.
Definition: Dynamic equilibrium is reached when the rate of molecules moving in one direction equals the rate of molecules moving in the opposite direction, resulting in no net movement.
Understanding these diffusion processes is crucial for comprehending how cells maintain homeostasis and exchange materials with their environment.
