Hi. In this video, we're going to be talking about acids, bases, and buffers. So, acids and bases are molecules found in cellular aqueous solutions. Now these are things that you talked about before in your introductory biology and chemistry classes, but we're just going to very quickly review them, what it means for cell biology. So first, acids are substances that release positively charged hydrogen ions into solution. The hydrogen gives up its electron for some type of reaction, leaving a positively charged proton in the solution. Hydrogen ions then can form interactions with water to create H3O+, which is called a hydronium ion. Now, there can be strong acids, and there can be weak acids. The difference is that weak acids do not completely dissociate in solution, whereas strong acids will, leaving their hydrogen to be floating around with this positive, this very strong positive charge. Now bases are substances that accept positively charged hydrogen ions. So acids release hydrogen into solution, and bases accept them. Like acids, there are strong and weak bases, and weak bases only partially associate in solution.
We talk about water a lot, so water can act as an acid or a base. It's not necessarily important that you understand the different situations in which that happens. We can talk about them as the class moves on. Just know that, if you get a question, "Is water an acid or base?" it's kind of a trick question because it can act as both. So, here we have this acid in this water solution, and you can see that it's sort of just floating around. It has this hydrogen ion, and then when it's put into water, the solution becomes acidic because it releases these hydrogen ions. Now a base, you can see, has these hydroxides. These are actually called hydroxides, but they are OH- molecules. So when they are released into water, they can release these OH-. And what do H+ and OH- make? H2O, which you can imagine forms very easily and can take up these hydrogen atoms in solution. Acidic solutions have high H+ and basic solutions have high OH-, so that they can take up the hydrogen atoms.
Now we measure acidity through this pH scale, and I know that you have seen this before. But, you can see here that if going through pH is measured, 0 to 14 is a logarithmic scale, and it measures the concentration of hydrogen ions to hydronium ions, so H3O+. So here you can see that all of this over here is very acidic. It has, what we term a low pH. Here at 7, it's going to be neutral. And this is generally where water resides a lot. And then from, you know, 8 to 14 we have this basic. And you can see that the color is actually becoming stronger, because as the pH gets larger for basic or smaller for acidic, it also becomes stronger. So a pH of 1 is going to be a really strong acid, whereas a pH of 6 is going to be a weak acid. And different compartments that cells have in them all have different pHs. So, in the cytosol, which usually averages about a pH of 7.2. You can imagine this is really a neutral pH, in the cytosol. Whereas if we look at in the lysosome, it has a very acidic pH at 4.5. And we'll talk about why this is important, but remember, the lysosome is important for breaking down and destroying materials. You can imagine why an acid compartment would be really important if you wanted to destroy a lot of materials.
Now we've talked about acids and bases, so let's talk about buffers. And so buffers are solutions that limit changes in the pH of a solution. They are composed of both weak acids and weak bases that can either accept hydrogen ions or release hydrogen ions as the pH tries to change. And so when the pH is trying to change by either accepting those or releasing them, they can adjust the pH, and really keep changes to a minimum. Buffers are crucial in cell biology because they are super important in keeping various cellular compartments or various tissues at a certain pH that it has to be for its function. And so one of the best ways to do this is through blood. So blood pH has to be a very specific pH, and it's balanced by this weak carbonic acid and a weak conjugate base. So as hydrogens are introduced or taken up by the blood, the pH tries to change and, it can't because you have these weak carbonic acids, which you can see here, and these weak conjugate bases, which you can see here sort of taking up and releasing these hydrogens. Now, you don't need to know this chemical reaction. You don't need to know these steps. Just sort of understand that these pH processes and buffers are really working in our body all the time to keep everything functioning normally. So now let's move on.
