Question

Describe the three kinds of stimuli that are responsible for the opening and closing of gated ion channels in animal cells

Discuss the general characteristics of porins and explain how these are similar to/or different from ion channels

Discuss the transport of water molecules via aquaporins, taking into consideration the effect of having an increased number of aquaporin proteins on a cell that would not typically express high levels of this protein.

Explain the difference between facilitative uniporters, symporters, and antiporters

Answer 1

A stimulus is a change detected by the body.

Heat, light, sound and pressure are the stimuli detected by sensory receptors.

Porins are transport proteins which facilitates transport of water between cells.

Cell membranes contains porins .

It forms wide aqueous channels allowing easy access of small, water soluble molecules from the surrounding to diffuse through the phospholipid layer.

Aquaporins permeable to water, but impermeable to ions. These are open channels.

Water molecules traverse through the pore of the channel in single file.

Ion channels are ion selective and flactuate between open and closed states.

Water flows the direction of osmotic pressure across the membrane through passive process in cells with aquaporins. Most cells do not express aquaporins. Membranes are water potential as a result water diffused through membrane lipids, such that cell volume euilibrates in response to an osmotic gradient.

Solute transporters help to facilitate the movement of water soluble solutes through the lipid bilateral of the membrane.

Types:

Uniporter: Involves facilitated diffusion through ion channels or carrier proteins.

Antiporter: It is a cotransporter involves secondary active transport of two or more different molecules or ions(Na+/Ca2+).

Symporter: Transports many different types of molecules across the cell membrane.

Molecules travel in same direction in relation to each other, contrast to antiporter.