Video transcript- In the first video where we introduced the idea of diffusion and concentration gradients, we had a container with only one type of particle in it, we had these purple particles. And in our starting scenario we had a higher concentration of the purple particles on the left-hand side than we had on the right-hand side. And so if we looked at its concentration gradient, so the concentration gradient went from high concentration on the left to low concentration on the right. And we saw what happened. Since you have more of these particles here and they're all bouncing around in different directions randomly, you have a higher probability of things moving from the left to the right than from the right to the left. You will have things move from the right to the left, but you're going to have more things, so you'll have a higher probability of things, moving from left to right. And so if you let some time pass, then they become more uniformly spread across a container. They have moved down their concentration gradient to make things more uniform. Now, what's interesting about this diagram is I've introduced a second particle, these big yellow particles. And we see that their concentration gradient is going in the other direction. So we have a low concentration, in fact we have no, on the left-hand, we have none of the yellow particles on the left-hand side, and we have a high concentration on the right-hand side. So their concentration gradient goes from right to left. And the whole point of this video is to show that each particle moves down its unique concentration gradient, assuming that it's not blocked in some way, it's going to move down its unique concentration gradient irrespective of what the other particles are going to do, for the most part. And so we see the yellow particles are going to move from high concentration, to low concentration. They're going to move, they're going to diffuse from right to left. And once again, there's no magic here. It's not like this molecule is saying, oh, I've got seven other of my friends here, it's getting too crowded, I see them, I'm claustrophobic, let me move over to the left-hand side. That's not what's going on. They're just all randomly bouncing around and when you're in the starting position, when you're exactly like this, there's no probability because of a yellow particle moving from left to right, because there aren't any yellow particles here. While there's a probability that some of these particles, in a certain amount of time, some of these yellow particles could move from right to left. And so they'll keep doing that until you get to a stable configuration where now you have an equal probability of things moving from left to right, and right to left. And that's going to be true for each of these particles. So the real takeaway, you'll hear in a biology or a chemistry class, of things moving down their concentration gradient, and you might say, and their unique concentration gradient. As you see, the yellow particles' concentration gradient goes in the other direction as the purple particles, but there's no magic to this. You just have to imagine a bunch of things just bouncing around in a bunch of different directions, and then what would just naturally happen? You would naturally have a higher probability of moving from high concentration to low concentration, than from low concentration to high concentration. Show  Concentration gradient
What is a concentration gradient? A gradient is a measure of how steep a slope is. Thus, a concentration gradient would be associated with the extent of the differences in the concentrations from one area to another. Let us understand what concentration gradient is, and its essence in biology. Concentration gradient refers to the gradual change in the concentration of solutes in a solution as a function of distance through a solution. A solution, essentially, has two major components, the solvent (the dissolving component, e.g. water) and the solute (the particles that are dissolvable by the solvent). In biochemistry, concentration pertains to the amount of a sub-component of a solution, e.g. the amount of solutes in a solution. Gradient, in turn, is a term that in general refers to the progressive increase or decrease of a variable with respect to distance. In this regard, a concentration gradient would be the outcome when the amounts of solutes between two solutions are different. In biology, a concentration gradient results from the unequal distribution of particles, e.g. ions, between two solutions, i.e. the intracellular fluid (the solution inside the cell) and the extracellular fluid (the solution outside the cell). This imbalance of solutes between the two solutions drives solutes to move from a highly dense area to a lesser dense area. This movement is an attempt to establish equilibrium and eliminate the imbalance of solute concentrations between the two solutions. Watch this vid on concentration gradients: Etymology: The term concentration comes from the word concentrate, from the French concentrer, from con– + center, meaning “to put at the center”. The word gradient comes from the Latin gradiens, from gradior, meaning “to step” or “to walk”. Synonym: density gradient. Biological TransportIn biological systems, there are two major transport phenomena: passive transport and active transport. In passive transport, particles (e.g. ions or molecules) are transported along the concentration gradient. This means that the particles move from areas of high concentrations to areas of low concentrations. Because of the passive movement of particles no chemical energy is spent as it takes place. Examples of passive transport are simple diffusion, facilitated diffusion, filtration, and osmosis. Conversely, active transport is the transport of particles against the concentration gradient. This means that the particles are moved from an area of low concentration to an area of high concentration. Because of this, chemical energy is spent to move the particles to an area that is already saturated or dense with similar particles. Concentration Gradient and DiffusionFigure 4: In biology, a concentration gradient results from the unequal distribution of particles (e.g. ions) between two solutions, i.e. the intracellular fluid (the solution inside the cell) and the extracellular fluid (the solution outside the cell). The particles may move along or against their concentration gradient. The downhill movement of particles is called passive transport (e.g. simple diffusion). Conversely, the uphill movement is referred to as active transport. Simple diffusion is a type of passive transport that does not require the aid of transport proteins. Since the movement is downhill, i.e. from an area of greater concentration to an area of lower concentration, a concentration gradient is enough to drive the process. A neutral net movement of particles will be reached when the concentration gradient is gone. That means that the equilibrium between the two areas is reached. The amount of particles or solutes in one area is similar to that of the other area. In facilitated diffusion, the process needs a transport protein. Similar to simple diffusion, it is driven by a concentration gradient and equilibrium is attained when there is no longer a net movement of molecules between the two areas. In many cases, though, the concentration gradient is not the lone factor in passive transport. For example, the presence of two different solutions on the external surface of the cell would have two different degrees of saturation and solubility. For instance, small lipophilic molecules and nonpolar gas molecules could diffuse more readily through the lipid bilayer of the cell membrane than polar molecules, including water. Concentration Gradient and OsmosisOne of the molecules that require a transport protein to move down the concentration gradient across a biological membrane is water. Osmosis is similar to diffusion as both of them are characterized by a downhill movement. The difference lies though in the particle that moves. In diffusion, it is about the movement of solutes. In osmosis, it is about the movement of the solvent, i.e. water molecules. In osmosis, the water molecules move from an area of high concentration to an area of low concentration. The pressure that drives the water molecules to move in such a manner is referred to as the osmotic gradient. But in order to move across the cell membrane, it has to use a channel protein in the cell membrane. This transport protein spans the entire membrane and provides a hydrophilic channel through which water molecules could pass through. Water is a polar molecule. Thus, it cannot easily pass through the hydrophobic lipid bilayer component of the cell membrane. It will, therefore, need a transport protein to move across. Nevertheless, since the movement is downhill, no chemical energy is required. Concentration Gradient in Active TransportFor active transport, the particles are transported in an uphill movement. This means that they move against their concentration gradient, i.e. from an area of lower concentration to an area of higher concentration. Because the movement is uphill, this process requires chemical energy. Active transport may be primary or secondary. A primary active transport is one that uses chemical energy (e.g. ATP) whereas a secondary active transport uses an electrical gradient (i.e. a gradient resulting from the difference in charge across a membrane) and a chemical gradient (i.e. a gradient formed from the unequal concentrations of solutes). An electrochemical gradient is a gradient of electrochemical potential for an ion that can diffuse into or out of the cell via the cell membrane. Since ions carry an electric charge, their movement into and out of the cell affects the electric potential across the membrane. If a charge gradient occurs (i.e. a gradient formed from an unequal distribution of electrical charges), this incites the ions to diffuse downhill with respect to charges until equilibrium on both sides of the membrane is achieved. (1) Examples of Concentration Gradient
Ion gradients, such as Sodium/Potassium gradients, are an example of a concentration gradient essential to cells. Neurons, for instance, have a Sodium/Potassium pump that they use to maintain a resting membrane potential (usually ranging from -60 to -90mV). Two major key players are sodium (NA+) and potassium (K+) ions. First, 3 Na+ ions inside the cell bind to the pump protein. Second, ATP phosphorylates the pump causing it to change its conformation, thereby releasing the 3 Na+ ions to the outside of the cell. Finally, one K+ ion from the outside binds to the pump protein and then released into the cell. The phosphate from ATP is also released causing the pump protein to return to its original conformation. Through this mechanism, the cell is able to maintain its inside to be more negative than the outside. (2) Neurons need this for action potential formation.
A proton gradient (also called H+ gradient) is a gradient that forms from differences in proton concentration between the inside and outside of a biological membrane. A proton pump is the membrane protein that transports protons (H+) across a membrane and is thereby responsible for building up a proton gradient. This gradient is essential to many organisms as it stores energy. For instance, it is the mechanism used in oxidative phosphorylation of cellular respiration. The proton pump transports protons from the mitochondrial matrix to the inter-membrane space. As a result, there are more protons outside the matrix than the inside. This leads to a proton concentration gradient across the inner membrane of the mitochondria.
In animals, respiratory gases such as oxygen and carbon dioxide form a concentration gradient when these gases differ in concentrations between the blood and the tissue fluid. These gases move downhill across the capillary beds.
References
© Biology Online. Content provided and moderated by Biology Online Editors |
What does moving down the concentration gradient mean?
Related Posts
Copyright © 2024 ShotOnMac Inc.
