Structural specificity: Each facilitated diffusion carrier protein has one or more binding sites for the molecules it transports, and can only recognize one or a type of substrate with a specific chemical structure.

Saturation phenomenon: The number and transport rate of carrier proteins in the cell membrane are limited. When the concentration of the transported substrate increases to a certain level, all binding sites will be When it is full, the diffusion rate of the substrate reaches the maximum value and no longer increases with the increase of the concentration of the substrate, which is called the saturation phenomenon of carrier transport. The maximum diffusion rate can reflect the maximum rate of conformational transformation of the carrier protein. The substrate concentration at which the diffusion speed reaches half of the maximum speed is called the Michaelis-Menten constant, which reflects the affinity of the carrier protein to the substrate molecule. The smaller the Michaelis-Menten constant, the higher the affinity and transport efficiency, and vice versa.

Competitive inhibition: The binding of the transported substrate to the carrier protein can be specifically blocked by competitive inhibitors; it can also be blocked by non-competitive inhibitors.

Efficiently absorb nutrients

Maintain intracellular ion balance

Participate in nerve signal transmission

Regulate physiological functions of cells

Respond quickly to environmental changes

Regulate cell osmotic pressure

Features

type

biological significance

Features

type

biological significance

Ion channel proteins mediate passive transport. The channel is bidirectional. The net flux of ions depends on the electrochemical gradient. The channel protein does not bind to solute molecules during the transport process.

Ion channels are highly selective for the size and charge of the transported ions.

High transport rate

Most ion channels are not continuously open. The opening of ion channels is controlled by a "gate", that is, the activity of the ion channel is regulated by the channel's open or closed configuration to respond appropriately to certain signals.

Regulates cell excitability, such as nerve signal transmission and muscle excitation and contraction.

Maintain ion balance inside and outside cells, as well as nutrient absorption and metabolic product excretion.

Regulates heart rhythm and vasomotion.

Synaptic transmission and gap junction communication are possible.

Realize mechanical sensing and chemical sensing.

Water channels are membrane channel proteins that sustain transport.

Shipping speed is fast.

The direction of movement of water molecules is entirely determined by the osmotic pressure difference on both sides of the membrane.

Maintain cellular water balance.

Participates in glandular secretion and absorption.

Regulates water metabolism in the kidneys.

Affects the function of the reproductive system.

Essential for plant water uptake and survival.

Functions in the nervous system.