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Monomers
Monomers
You're going to be hearing the term monomer a lot in this class, particularly in this unit. According to your textbook, a monomer is a single subunit that can be chained together to form a larger molecule (a polymer). This is a great definition, but it sounds way more complicated than it is. So let's break it down: a monomer is essentially a building block - it's like a Lego. You can put multiple Lego's together to create an entirely different thing. Sometimes, the thing you create is huge, or very intricate. That is going to be very important as we start to see increasingly complicated macromolecules. The names are easy to remember. Mono means one, and poly means many. So a monomer is one piece, and a polymer is made of many.
Polymers
Polymers
Just to reiterate, a polymer is a group of monomers chained together. Sometimes the chain formed is very simple, perhaps just a straight line, as seen in the image shown here. Sometimes, a polymer may be a ring shape, or virtually any shape you can imagine. The chain can be an immensely complicated and intricate 3-dimensional shape (well, molecules are always 3-dimensional, but that become even more crucial to consider with proteins) as shown here.
Notice in these images (particularly the straight molecule) that you can see a regular, repeating pattern within the molecule. That chain is made up of a bunch of monomers put together. That is why it looks so similar all the way through. Think about railroad tracks - the long track (polymer) is made up of a bunch of smaller pieces of wood and metal. In that case, the long railroad track looks very consistent all the way down.
Why does the molecule on the right look so different, then? Well, sometimes we don't just use the one monomer type. Sometimes we want to use something different. It would be like creating a railroad track out of wood for some areas and metal for others. That could be useful if some areas of the track were over water, or were in colder areas, for instance. Changing the subunits (monomers) changes the structure and function of the whole molecule (polymer).
So how do we chain together monomers to form these polymers? Well, we use polymerization reactions (a term used by your book that you should be familiar with, but don't worry too much about) - that's literally what that name means. But, specifically, we use a process that goes by two names: dehydration synthesis a.k.a. condensation reactions. Why do we have two names for the same thing? Well they are technically a little different, but that doesn't matter to us - we just wanted to give you more vocabulary to know, duh.
Dehydration Synthesis (a.k.a. Condensation Reactions)
Dehydration Synthesis (a.k.a. Condensation Reactions)
What is it, exactly?
What is it, exactly?
Okay both of these names sound too long and overly complicated. Let's break them down:
Dehydration Synthesis
Dehydration - lack of water
Synthesis - creating something from other materials
Condensation Reactions
Condensation - water drops collect from water vapor (often seen on a glass of ice water)
Reactions - chemical change or reactants combining to form products
If I had one piece of advice for you in biology, it would be to think about what the words mean - we generally call them that because it makes sense. This is no different, as you will see once you see a little more of the process in action.
Dehydration Synthesis is basically just forming a bond between two monomers. Okay, so that's the synthesis part. Where does the dehydration come in? Well, in order to form a bond between these two molecules, we have to cut them to the right size first. Observe the image here of a simplified diagram of the process.
Essentially, those two monomers on the left are perfectly happy on their own. If we want to attach them together, we have to spend some energy in order to form that bond. That energy allows us to form a chain of monomers, but the atoms we chopped off of the monomers have to go somewhere. The hydrogen of one monomer and the hydroxyl (OH) of the other combine to form water. H + OH --> H2O. Simple enough. That's where the water in the name comes from. We are taking water out of the monomers - we are dehydrating them. This allows us to make, or synthesize a larger molecule. Hence, dehydration synthesis.
The diagram above was a simplified form of this. It is chemically accurate, but we used simplified molecular diagrams that you may or may not be familiar with. A more detailed version could look like this:
If you get take two molecules of glucose and you want to string them together, you have to take out an H from one and an OH from the other, resulting in water plus a maltose (just a larger sugar molecule). In this example, glucose is a monomer and maltose is a polymer.
So why do we do this?
So why do we do this?
Well, it's nice to be able to string together molecules because it means we can store some of their energy. Or sometimes we need a large molecule to do a particular job. We will explore this more when we talk about enzymes.
Think about it evolutionarily - if you ate a lot of extra glucose because you happened to find a lot of fruit on a fruit tree, wouldn't you want to be able to eat the fruit and store that energy for later? That's why we store fat. If we overeat, we will take those molecules (whether they be glucose or others), break them down, and then build them up into fats so we have that energy later when we need it. This was really great when we didn't know when our next meal might be, but in most first-world countries where food is readily accessible to most people (still not all, unfortunately), this can be seen as a nuisance.
Hydrolysis
Hydrolysis
What is it, exactly?
What is it, exactly?
Hydrolysis is another one of those terms that we should break down to figure out what it might mean - this is a really useful thing to do on tests, by the way. Breaking it down, I see:
Hydro - water
Lysis - 'lys' means to cut or break down (this is part of our Ring of Roots assignment for a reason!)
So, we are using water to break something down...
Before, we pulled water out of two monomers and formed a polymer. That was a chemical reaction. Chemical reactions are often reversible. So what if we did the opposite?
I'm going to take a polymer and try to break it up into its subsequent monomers. In order to do this, I'm going to need a water molecule. I can't just chop off that bond that holds the monomers together - then the molecules wouldn't be stable. If I am going to stabilize the molecules, I'm going to add an H and an OH, just like what we removed last time.
So, to recap, hydrolysis is the exact opposite of dehydration synthesis. Think of it much like how 'hydro', or water, is the opposite of 'dehydration', or the lack of water. This inverse relationship is well-represented in this diagram.
Why would we just undo what we spent energy doing?
Why would we just undo what we spent energy doing?
Well, what if we want to get that energy out? Or what if we consumed a polymer? You do consume polymers - a lot of them - in your diet. Polymers are difficult to use - they're big, so it's hard to get them into cells (more on that later). It is much easier to break them down first. We do this via hydrolysis. Once the molecules are smaller, we can use them more easily.
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