Give any two characteristic features of transport through special proteins in facilitated diffusion.

Facilitated diffusion uses membrane carrier proteins (transporters) or channel proteins to move substances across membranes along their concentration gradient. Two key characteristics:

Feature	Explanation
1. Specificity	Each carrier protein is highly specific for particular molecules or ions. Example: GLUT transporters specifically bind glucose, not other hexoses. This specificity arises from the precise 3D structure of the binding site.
2. Sensitivity to Inhibitors	Transport proteins can be inhibited by specific chemicals that compete for binding sites or alter protein conformation. Example: Mercury ions (Hg²⁺) inhibit aquaporins (water channels).

Additional Characteristics:

1. Saturation Kinetics: Rate of transport reaches maximum (V_max) when all carriers are occupied (follows Michaelis-Menten kinetics)
2. No Energy Requirement: Unlike active transport, facilitated diffusion is passive (ΔG < 0)
3. Faster than Simple Diffusion: 10⁴–10⁵ times faster for polar/charged molecules

Examples:

• Channel proteins: Aquaporins (water), ion channels (K⁺, Na⁺, Ca²⁺)
• Carrier proteins: Glucose transporters (GLUT), amino acid permeases