Condensation & Hydrolysis Reactions – TRANSCRIPT

Well, let’s start with some definitions, again – mega important in A level biology. I will highlight the ones where you will have to give a definition in an exam. For pretty much all the key terms, we need to be able to recognise, know what they mean, and be able to use them, but most of the time we don’t have to give the definitions.

So condensation: Joins two molecules together, with the formation of a chemical bond, and it involves the elimination (or the removal) of a molecule of water.

Okay, so I’m going to draw some examples here using carbohydrates, but this could well be lipids…any of the biological molecules: could be triglycerides, proteins, it could be nucleic acids…pretty much anything. There are only two types of reactions. So these are both types of reaction and if you get asked what type of reaction is this, you’ve got a choice of two: is it condensation joining things together or hydrolysis splitting things apart?

I’m gonna start by drawing the molecules (and see how neatly I can do them). I’m going to draw the bits that are involved in the bond in red, but actually let’s complete the molecule first. I’m just leaving a little bit of a gap there for a reason…these are just, it’s an OH group that’s just like any other. And right next to it. I’m gonna draw my other molecule of glucose, so that we’re going to attach onto it here in this condensation reaction.

Okay, so here I’ve got two molecules. It happens to be alpha glucose, and you can see I’ve highlighted some of…I could have chosen both the OH here and just the hydrogen here, doesn’t matter which way around but what you can’t do is take one of the single hydrogens and bond it on to the OH group over here. It’s always between the two OH groups. And in this case, I’m just exemplifying it this way around.

So these are the ones that are involved in forming that molecule of water. O, oxygen, two hydrogens: H2O gives us our molecule. So this is glucose and technically it’s alpha glucose. This is Alpha (Greek symbol) alpha glucose and alpha glucose, and they react together to form maltose, which I’ll draw next. So again, I’m starting from this end of the molecule, drawing it from left to right, so here I’m drawing the left…and then the bond is…this is a carbon atom onto an oxygen atom onto the carbon atom on the next molecule.

And this molecule is maltose. If I was asked to draw this in the exam I would not have full marks at this point because, what have I forgotten? I have eliminated two hydrogens and oxygen and I have not drawn them in and so they need to be included. If you get asked the question to draw this, which is not a common question, but if you do, then if it’s a condensation reaction, you’ll have to draw the molecule of water and if it’s a hydrolysis reaction, you’ll have to include the molecule of water there as well. So these, and this is water.

Okay, this name of this bond we’ll dive into more in another video. But this is a glycosidic bond.

If ever you’ve got a bond joining any of the carbohydrates, then it’s a glycosidic bond. And you don’t really need to know its full structure. And if I do go into that, it’ll be in another video.

Okay. So what’s the opposite of a condensation reaction? Well, it’s a hydrolysis reaction.

So this breaks a chemical bond between two molecules using a molecule of water. Okay, so the difference here: we eliminate one, we produce one in other words: It’s one of the products, and here we’re going to use one. It’s going to be one of the reactants, if you want anything in it from a chemistry perspective, again, I’m going to draw my molecule of maltose. It’s going to be exactly the same as the one I’ve drawn up here.

Okay, this is my maltose. What do we need to add in to go back to where we were, well, we’re going to need a molecule of water. And now we’re gonna draw two molecules of alpha glucose. So this is good practice, this, it’s not a very common question, but you are required to know the basic structure of alpha glucose. So it’s good practice to see if you can draw these ones or just have a quick glance, see what you’ve got going on up here cover it up, try and do it from your memory and write it down on your own, or at least maybe sketch them on a side pad and then get your neat copy of the notes correct.

So we’ve got… And let’s label them up. In order to make this reaction happen in reality, (we’re talking about the subject of biology and living organisms), there’s going to be an enzyme involved, called maltase. So we’ve got maltose, which is our molecule, here. And we’re gonna yeah, the difference, let me write it out because it’ll be more obvious. And in fact, I’m gonna write this in block capitals, a tiny little bit of exam technique for you, here.

We would also use the enzyme maltase and obviously if I’d written this as a lowercase ‘a’ and a lowercase ‘o’, there’s very little difference between them. The exam boards are super lenient in accepting misspellings, as long as it’s obvious what you’re trying to write, but if they can’t read your handwriting and A’s and O’s can easily be confused. You can see they will not give you the benefit of the doubt, there. So it’s sometimes a good idea if you’re writing an answer involving maltose and maltase, (which is reasonably common), to write maltose or maltase in capital letters, or at least the A in the O in such a way that they can definitely tell what you are talking about.

Okay, so quick summary: condensation joins two things together. We eliminate (or get rid of) a molecule of water. You have to draw it in, should you get asked to do that. This would be the case for any of the biological molecules and it’s one of the only two types of reaction you need to know. Hydro lysis, we can break this word down: lysis means to split or to break (so to split) and then it’s using the thing that’s in front of the word lysis. So if you have hydro lysis using water to split apart another molecule. Later on in the course, in photosynthesis will come across photo lysis or photolysis and that is splitting using light energy and we might have osmotic lysis which is when cells burst due to osmotic pressure. So lysis means to split and the thing that comes in front of the lysis is what’s causing the splitting to happen. Be careful with your ‘Ose’s and your ‘Ase’s that comes up really commonly and, yeah, that in a nutshell is condensation and hydrolysis reactions.