12 Questions
What type of proteins facilitate the massive diffusion in plant and animal cells?
Aquaporins
Which type of channel proteins open or close in response to a stimulus?
Gated channels
Without the high number of aquaporins in certain kidney cells, what would be the consequence in terms of urine production?
Excreting about 180 L of urine per day
Which type of proteins seem to change shape to translocate the solute-binding site across the membrane?
Carrier proteins
What type of transport protein brings about a tremendous increase in the rate of water molecules passing through the cell membrane?
Channel proteins
Which type of transport protein holds onto its passengers and changes shape to shuttle them across the membrane?
Carrier proteins
What determines the selectivity of a carrier protein in transporting substances across the membrane?
The specificity of the carrier protein
Which molecules can cross a lipid bilayer without the assistance of membrane proteins, as mentioned in the text?
Oxygen and carbon dioxide
Why is a transport protein needed to move water molecules rapidly and in large quantities across a membrane?
To increase the speed at which water molecules can cross the membrane.
Based on the text, what is the main function of aquaporins?
To enable the passage of water and certain other substances across membranes.
What is the basis of the selectivity that allows some aquaporins to exclude hydronium ions but allow glycerol and water molecules to pass?
Hydronium ions are closer in size to water than to glycerol.
What happens in the process of diffusion when two solutions reach dynamic equilibrium?
Molecules cross the membrane at equal rates in both directions.
Study Notes
Protein-Mediated Transport
- Channel proteins facilitate massive diffusion in plant and animal cells.
- Ligand-gated channel proteins open or close in response to a stimulus.
Aquaporins and Urine Production
- Aquaporins are responsible for transporting water molecules across the cell membrane.
- Without a high number of aquaporins in certain kidney cells, urine production would decrease.
Carrier Proteins
- Carrier proteins seem to change shape to translocate the solute-binding site across the membrane.
- Carrier proteins bring about a tremendous increase in the rate of solute transport across the membrane.
Transport Mechanisms
- Transport proteins are needed to move water molecules rapidly and in large quantities across a membrane because the lipid bilayer is impermeable to water.
- Some transport proteins hold onto their passengers and change shape to shuttle them across the membrane.
Selectivity of Carrier Proteins
- The selectivity of a carrier protein in transporting substances across the membrane is determined by the shape and chemistry of the binding site.
- Some aquaporins exclude hydronium ions but allow glycerol and water molecules to pass due to the basis of their selectivity.
Diffusion and Dynamic Equilibrium
- In the process of diffusion, when two solutions reach dynamic equilibrium, the movement of molecules from one solution to another becomes equal in both directions.
- Small molecules, such as oxygen and carbon dioxide, can cross a lipid bilayer without the assistance of membrane proteins.
Learn about the role of aquaporins, water channel proteins, in facilitating rapid diffusion of water and ions across cell membranes. Understand how certain cells like red blood cells and kidney cells utilize aquaporins to manage water balance and prevent excessive water loss.
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