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the protein molecule to the other side of the cell membrane. Eventually, the solute molecule is released to the other side of the membrane. ‒ Channel proteins interact weakly with the material to be transported. If the channel is open, specific solutes can freely pass through them. AQA A-Level Biology 3.2.3 Transport across cell membranes
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National 5; Transport across membranes The cell membrane. All cells are enclosed by a cell membrane, which is selectively permeable. Molecules can move into or out of cells by diffusion and active ...
The flow of water across a membrane in response to differing concentrations of solutes on either side - osmosis - generates a pressure across the membrane called osmotic pressure. Osmotic pressure is defined as the hydrostatic pressure required to stop the flow of water, and thus, osmotic and hydrostatic pressures are, for all intents and purposes, equivalent.
- Diffusion
- Diffusion Through Membranes
- Role of Electric Forces on Ion Movement
- Diffusion Through The Lipid Bi-Layer
- Diffusion of Ions Through Protein Channels
- Regulation of Diffusion Through Ion Channels
- Mediated Transport Systems
- Facilitated Diffusion
- Active Transport
- Osmosis
Diffusionis essentially the movement of molecules from a region of higher concentration to a region of lower concentration as a result of thermal motion. Diffusion is an important process in human physiology. Specifically, diffusion is the mechanism of movement of oxygen, nutrients and other molecules across the capillary walls and the movement of ...
The magnitude of net fluxcan be measured as: F= kpA(C0 – Ci) where, kp = permeability constant for a particular molecule at a particular temperature A = surface area of membrane C0 = extracellular concentration of the substance Ci = intracellular concentration of the substance Remember that membranes slow down diffusion and molecules will move slow...
The membrane potential is the separation of electric charges across a membrane. The separation of charges influences the movement of ions across the membrane. This can act independently of or in conjunction with, or in opposition to, the force generated by concentration differences. The electrochemical gradient refers to these two forces collective...
Non-polar molecules can dissolve in the non-polar fatty acid chains of the membrane phospholipids and therefore non-polar molecules have larger permeability constants than polar molecules.
Protein channels formed by integral proteins allow ions to diffuse across the membrane. Different cells have different permeabilities to these ions. The diameter of the channel and the polar groups on the protein subunits forming channel walls determine the permeability of the channels by various ions and molecules.
Channel gating is the opening and closing of ion channels which changes the permeability of a membrane. It is controlled by three modulators: 1. Modulation of allosteric or covalent channel-proteins in ligand-sensitive channels 2. Modulation of channel proteins due to changes due to changes in membrane potential in voltage-gated channels. 3. Modula...
There are integral membrane proteins called transporters that mediate movement of molecules that are too polar or too large to move across a membrane by diffusion. In order to accomplish this, a solute (molecule to be transported) binds to a specific site on a transporter on one surface of the membrane. The transporter then changes shape in order t...
Facilitated diffusion moves solutes from a region of higher concentration to a region of lower concentration until the concentrations become equalized on both sides of the membrane.
This form of molecule movement requires energy in order to move solute against its electrochemical gradient. Energy is required to either: 1. Alter the affinity of the binding site on different sides of the membrane 2. Alter the rates at which the binding site on the transporters is shifted from one side of the membrane to the other. Furthermore, t...
Osmosisis the net diffusion of water across a membrane. Aquaporins are proteins that form channels in the lipid bi-layer for the polar water molecules to diffuse through. There will be a net diffusion of both compartments leading to diffusion equilibrium with no change in volume in either compartment if the compartments are separated by a membrane ...
The latter controls the opening of the channel. Various mechanisms may be involved in the gating mechanism. For instance, the attachment of a specific ion or small molecule to the channel protein may trigger opening. Changes in local membrane "stress" or changes in voltage across the membrane may also be triggers to open or close a channel.
Filtration is another passive process of moving material through a cell membrane. While diffusion and osmosis rely on concentration gradients, filtration uses a pressure gradient. Molecules will move from an area of higher pressure to an area of lower pressure. Filtration is non-specific.
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Molecules move in and out of cells in one of three ways: passive diffusion, facilitated transport and active transport. Only a few small, relatively uncharged molecules can cross a membrane unassisted (i.e., by passive diffusion). Hydrophilic molecules that must enter or leave cells do so with help, i.e., by facilitated transport.
