Lesson video

This lesson is called Biological molecules and is from the unit Biological molecules and enzymes.

Hi there, my name's Mrs. McCready, and I'm here to guide you through today's lesson, so thank you very much for joining me.

In our lesson today, we're going to learn about carbohydrates, proteins, and lipids, be able to describe them as polymers, and understand what they are made of.

In our lesson today, we're going to come across a good number of keywords, and they're on the screen now with their descriptions.

You may wish to pause the video now in order to make a note of them, but I will introduce each word as we come across them.

So in our lesson today, we're going to first take a look at carbohydrates, then we're gonna look at proteins, before we finish up looking at lipids.

So I hope you're ready to go.

I am.

Let's get started.

So before we carry on and look at carbohydrates in detail, we need to remember that organisms are made of many different things, including carbohydrates, proteins, and lipids, which also include fat, but also water and many different minerals.

And all of these molecules combine in many different ways to make our cells and the subcellular structures that make up those cells.

So you can see in that picture there are lots of different parts of a cell, which we've zoomed right in close to.

In fact, in there, we can see the nucleus and we can see some of the parts which feature in the cytoplasm.

And all of these parts, the cell membrane, the nucleus, the mitochondria, and all the contents of the cytoplasm combine together to make a cell, and a cell is a living organism.

And those organisms are made of these basic structures: carbohydrates, proteins, and lipids, being the focus of our lesson today.

So before we carry on, let's just check our understanding.

So which of the following in the list there on the screen are subcellular structures? Listed include carbohydrates, mitochondria, nucleus, and proteins.

I'll give you five seconds to think about it.

Okay, so hopefully, you have decided that both the mitochondria and the nucleus are subcellular structures, but carbohydrates and proteins are not.

So let's have a look at carbohydrates in a wee bit more detail.

Carbohydrates are molecules, and they are made up of carbon, that's shown in black in the diagram there on board, hydrogen, that's shown in white, and oxygen, shown in red.

And you can see how they're all put together to form what is considered a simple carbohydrate molecule, although actually, it looks relatively complicated.

So let's just have a quick look at this word, carbohydrate.

Carbo is the carbon section, hydro is short for hydrogen, and ate is the chemical shorthand for oxygen.

So if you ever see ate attached to the name of a compound, you know that it will include oxygen as well as other elements within it.

So carbohydrates are made of carbon, hydrogen, and oxygen.

And carbohydrates are therefore put together into things like simple sugars such as glucose, and also then combined over and over again into much, much more complex molecules such as starch.

So let's have a look at these in a bit more detail again.

Simple sugar molecules are called monosaccharides.

And here's another scientific term that we need to be familiar with.

So what does monosaccharide mean? Well, the word mono, you may well have come across before, and mono means one.

Saccharide is the scientific term for sugar.

You might have come across the word saccharin, being something which is very sweet or very sweet behaviour, or maybe saccharin as a sweetener for in tea and coffee instead of sugar, essentially.

So monosaccharides are single simple sugars, and they include a number of examples including glucose, which is the basic building block of starch.

Also, fructose, which you might not necessarily have come across as a word, but I'm sure you have great experience of having eaten lots of different types of fruit.

So fructose is the common sugar found in many fruit.

And galactose, again, probably not a sugar that you've heard of, but you will most certainly have come across it because when it's paired with another sugar, glucose, when galactose is paired with glucose, it forms the sugar lactose which you probably have heard of because that is found in milk, and many people we know are lactose intolerant.

You may be one of those who has to be careful of lactose.

So we've got a number of common monosaccharides here: glucose, fructose, and galactose.

So let's just quickly check which of those glucose, fructose, and galactose is commonly found in fruits like strawberries? I'll give you five seconds to think about it.

Okay, well hopefully, you have identified that fructose is the monosaccharide found in fruits like strawberries.

Well done.

Now we've seen that there are single sugars, monosaccharides, but we can put them together into much, much more complicated carbohydrates as well.

So if we join one monosaccharide to another monosaccharide, we get what's called a disaccharide.

So what does that word mean? Well, di means two, a bit like bi, bicycle, you know, two wheels.

Well, di is an alternative version of that.

Di, meaning two, and saccharide, well, we've seen that before, that means sugar.

So these are two sugar sugars.

So disaccharides come in a variety of forms as well.

Sucrose you will have come across, and you're probably familiar with that term as well.

Sucrose is made up of glucose and fructose, and this is what forms table sugar.

That white, crystalline sugar, that is sucrose, a disaccharide made of glucose and fructose.

We've also already mentioned lactose.

So this is a combination of glucose and galactose, and lactose is commonly found in milk.

And maltose is a combination of glucose and glucose, much less familiar perhaps, but is found in things like beer.

So sucrose, lactose, and maltose are all examples of disaccharides, two sugar sugars.

So let's just quickly check our understanding again.

How many molecules of sugar join to form a disaccharide? Is it none, one, two, or more than two? I'll give you five seconds to think about it.

Okay, so hopefully you've remembered that di means two, and therefore chosen that as your answer.

Well done.

Now we've seen how we can join one sugar with another sugar to form a disaccharide.

Well, if we keep adding sugars to each other, we can form what are called polysaccharides.

And polysaccharides are a form of polymer, that is, a very long collection of monomers, single sugars, in this case, joined together.

So, again, let's just check that word polysaccharide.

Well, poly, as in the word polymer, means many.

And saccharide, of course, we've come across, meaning sugar.

So these are many sugar sugars.

Now there are a good number of examples here, and let's have a look at those in a bit more detail.

Starch you will almost certainly have come across, and this is essentially lots and lots of glucose sugars all joined together in very, very long chains.

And plants store their carbohydrates in the form of starch within their plant cells and within special organs such as potatoes.

So if you dig up a potato, and when you are handling potatoes, cooking them, preparing them for cooking, they're absolutely packed full of starch.

And you know when you are peeling them and there's that kind of white oozy residue which kind of oozes out of them? Well, that is the starch.

That's the starch leaking out of the cells that you've damaged as you've peeled them.

Plants also have another form of glucose polymer, and this one is called cellulose.

So cellulose is another version of glucose joined end on end on end into very, very long chains.

But it's organised in a different way, and so has different properties from starch.

They're organised in extremely long chains, and then those chains are bound to each other and they form very, very strong, dense structures.

And because they're strong and because they're dense, they make excellent cell walls because they provide strength to the cells and help essentially keep the plant upright and in its shape.

'Cause remember, plants don't have bones or an exoskeleton either, so they need something to keep their shape, and cellulose can help with that.

Well, cellulose, because it features within plants, it is therefore the most common polymer on Earth, believe it or not.

That is incredible, isn't it? Now we've seen how polymers of glucose are joined together into starch and cellulose in plants.

Well, we can join them together in a different way and form another polymer called glycogen.

Now glycogen is stored in animal cells rather than in plant cells, and that's because it's heavily branched.

So you can see in the diagram there all the branches and the branches and the branches.

And because it is heavily branched, it means that it can be broken down extremely rapidly back down into individual single glucose monomers.

And that's very helpful for animals because animals often need a very rapid burst of energy, and it would take too long to break starch down because starch is just one single long length, and you'd only be able to break it down at either end.

It would take too long to release the energy required for an animal if we were using starch.

And so, we've got this heavily branched version called glycogen instead, which is much, much more accessible for releasing glucose rapidly, which is very helpful when you need to run away from something really, really quickly.

So let's quickly check that then.

Plants store carbohydrates as glycogen.

Is that true or false? I'll give you a few seconds to think about it.

So hopefully you've identified that as false, but can you justify your answer? Okay, so hopefully you've justified it by saying that starch is used as a storage molecule in plants, not glycogen, and not cellulose either, but starch is the storage molecule.

Well done.

So what I'd like you to do now is use all the information that you now know about carbohydrates, and you may well already have known quite a lot of that, and I'd like you to create an educational poster that's going to inform your reader about what carbohydrates are made from, what roles they have within cells, and anything interesting or notable particularly about specific carbohydrates such as glucose and lactose, for instance.

So in order to be successful with your educational poster, you need to include interesting and relevant information, it needs to be factually correct, it needs to include labelled diagrams. If you're going to include a diagram, make sure that you label both the parts of it and the overall diagram as well, please, and that you use good spelling and grammar throughout.

So pause the video now, spend some time and thought putting this poster together, remember it's got to interest and excite your reader and tell them lots of really interesting information about carbohydrates as well, and come back to me when you are ready.

Okay, so hopefully you've had a good chance at putting your educational poster about carbohydrates together.

So let's see what sort of things you might have included within it.

So your poster might have included things about what they're made from.

What carbohydrates are made from, such as carbon, hydrogen, oxygen, and the fact that monosaccharides are single sugars, disaccharides are two sugars joined together, and polysaccharides have many sugars joined together.

You might have included information about what roles they have, such as using carbohydrates for energy and for storage.

And you hopefully have listed some notable carbohydrates, such as glucose, fructose, and galactose as examples of monosaccharides, sucrose, lactose, and maltose as disaccharide examples, and starch, cellulose, and glycogen as polysaccharide examples.

So just review your poster.

Does it include lots of that information? Are your diagrams labelled? And is your spelling and your grammar good on your poster? Just review your poster now, and then we'll carry on when you are ready.

Okay, so what we're gonna have a look at now is proteins.

So proteins are complex polymers that are made from many, many smaller molecules called amino acids.

So there are plenty of amino acids.

There's about 20 different types of amino acids present within organisms, and they get joined together in all sorts of different orders into very, very long chains that then, when folded up into a complex shape, create a protein, and then that protein will have a specific job to do within the body.

Now one protein, therefore, is made up of many, many different amino acids.

Some proteins are quite small, maybe about 50 amino acids or so, and are therefore not particularly complicated, and they're quite quick to make as well because they're quite short.

Whereas, other proteins are extremely complicated, maybe thousands of amino acids all joined together, and maybe several different strands of protein chains then combined to make the whole protein.

So some can be extremely complicated indeed.

Now that order of amino acids is really vital because it determines the shape and the function that that protein will have.

So if we consider the protein found within muscle, the order that all of those amino acids are put in is determined by DNA stored within the nucleus of cells.

That's how important the order of the amino acids are, that it is coded into our DNA.

That's critical.

So have a think about that, and what I'd like you to do is to complete the sentences using some of the words listed.

So have a think about it.

I'll give you a few moments to work out what you're gonna put where, and then we'll restart when you are ready.

Okay, so let's review our work.

So you should have said that proteins are polymers made from amino acids.

DNA describes the order that they need to be assembled.

So check your work.

Have you got them all right? Well done if you have.

Now proteins take on many, many different roles within all organisms on Earth.

Some of those roles are structural, so building up parts of a body.

And some of those are functional, so doing a job within the body.

For example, keratin is a structural protein, and that's found in skin, hair, nails, that outer layer, that harder outer layer that forms a protective barrier between the external environment and the organism within.

That's keratin, that's a protein, and that's a structural example.

Haemoglobin is a different type of protein, and this is a functional protein because haemoglobin is quite a complex protein found within red blood cells, and haemoglobin is able to carry oxygen around the organism within the blood.

So haemoglobin is extremely important, but that is a functional protein.

Antibodies are also functional proteins, and these are really important in protecting animals from diseases by providing an immune response.

All of those examples are animal versions of proteins.

But plants have proteins too, and they have many different roles as well, just like they do within animals.

For instance, globulins are really important structural proteins that are involved in seed storage.

And there are a vast array of proteins in functional roles within plants, and they create protective films, they carry out photosynthesis, they provide immunity to the plant, they help to transport compounds around the plant, they carry out many, many different roles.

So proteins are as important within plants as they are within animals.

There's another type of protein as well, which are present in every organism, from the very, very simplest bacteria up to the most complicated organisms of plants and animals.

And these are enzymes.

And enzymes are a type of functional protein.

They carry out chemical reactions and they help to make chemical reactions go faster.

So we've seen a good number of different types of proteins present within plants and within animals, and we can conclude, therefore, that proteins are important for functions of growth and repair, they have functional roles and they have structural roles.

So let's quickly check our understanding of that.

Which of the following proteins are functional proteins? Globulin, antibodies, and haemoglobin are your choices.

I'll give you five seconds to think about it.

Okay, so what do you think then? Well, the following proteins: antibodies and haemoglobin are both functional.

Globulin is a structural protein found within plants.

Did you get them both right? Excellent job if you did.

Well done.

So what I'd like you to think about now is this scenario: so Lucas and Laura are having this conversation.

Vegetarian sausages contain more carbohydrates and much less protein than pork sausages.

They come across this piece of information, and they're discussing it.

Now Lucas says, "vegetarian sausages have more carbohydrate than protein because they contain more plant material." And Laura, in response to that, says, "Starch is a plant carbohydrate so I would expect vegetarian sausages to be really starchy." So what I would like you to do is to evaluate their discussion and identify how their comments could be improved.

So consider each student separately, look at what they've said, look at how it compares to what you know now about carbohydrates and about proteins, write a response for both Lucas and Laura, and then come back to me when you're ready.

Okay, so let's see.

Laura and Lucas are having this interesting discussion about vegetarian sausages, but how could their responses be improved? So Lucas has said, "Vegetarian sausages have more carbohydrate than protein because they contain more plant material." So you might have said then that vegetarian sausages contain much more plant material, which is why they contain more carbohydrates.

And an example of a carbohydrate in plants is cellulose.

But pork sausages contain much more protein because they are made from meat, which is made mostly of protein.

So in addition to Lucas's initial statement, you've added some comments about pork sausages as well.

Whereas, Laura said, "Starch is a plant carbohydrate so I would expect vegetarian sausages to be really starchy." Well, in response to her comments, you might have said that it's probably very unlikely the vegetarian sausages contain a lot of starch because starchy sausages would taste much more like potatoes.

They'd be quite like chip, really.

And therefore, because vegetarian sausages do not taste like potatoes, they obviously don't contain a lot of starch, therefore they must contain cellulose instead, which is a very common plant carbohydrate.

So you've just twisted what she said and pointed it in the right direction.

So just check over your work.

That was quite a tricky task to do, so I hope you've done well.

And well done for having a really good go at that as well.

It was really quite tricky.

So our last section today is about lipids.

So lipids are also biological polymers, therefore made up of many smaller units all put together.

And they include lots of different types, lots of different types of lipids.

So lipids is not necessarily a term you're particularly familiar with, but you'll be more familiar, certainly, with the term fats.

Now fats are solid at room temperature, things like butter and lard, for instance, are common fats that we come across on a daily basis.

And you can see the diagram there on the screen is an example of a triglyceride.

And a triglyceride is a type of fat.

There are also oils which are part of the lipid family.

And oils, as I'm sure you are probably familiar with, are liquid at room temperature.

Vegetable oils, for instance, are an example of an oil.

So grape seed oil, vegetable oil, olive oil, sesame oil, that kind of thing, they're all oils, and they're all from vegetables, and they're all liquid at room temperature.

Now lipids, because they've come in various different forms and they have various different properties, they feature in lots of different types of foods, including oily fish, nuts and seeds, cheese, butter and other dairy products, and oily vegetables such as avocado.

You will have come across lipids whether you have really realised it or not.

Now lipids are quite versatile in their structure, and they can be put together into many different shapes.

So for instance, some lipids have two fatty acid chains and one glycerol molecule.

You can see that in the diagram on the screen.

These two fatty acid chains are varying different lengths and have various different properties within them as well, and then the glycerol sits at the top and binds them together.

These types of lipids form cell membranes.

So when we talk about cell membranes, we are talking about a form of lipid like this.

That is what they are largely made up of.

There are other types of structures of fatty acids in glycerol.

So you could have three fatty acid chains bound to one glycerol, for instance.

And they have various other different uses, such as storing energy within cells, providing a layer of thermal insulation like blubber, such as we would find within animals which live in very cold environments such as whales and polar bears, and providing protection around vital organs.

So acting as a bit of a shock absorber, essentially, around things like the heart, the liver, the pancreas, the kidneys, that sort of thing.

So which of these is a use for lipids within an organism? Is it making cell walls, carrying oxygen, making cell membranes, or enzymes? I'll give you five seconds to think about it.

Okay, so hopefully you have chosen that making cell membranes is a use for lipids within organisms. Remember that cell walls are made from cellulose, carrying oxygen is a type of functional protein function, and enzymes are also made of proteins.

So what I'd like you to do next is to consider the three tasks here.

So firstly, I would like you to name the parts that lipids are formed from.

Remember, there are two different parts that lipids are made of.

Name these parts and draw a diagram to show how they're put together and label that diagram, as well, with those different parts.

Then, I'd like you to think about the different functions that lipids have within an organism.

And I'd like you to list three functions of lipids and I'd lik you to explain why these are really important to the organism.

And then finally, I would like you to think about the importance of lipids within our diet.

I'd like you to state three sources of lipids and explain why it is important to have a balanced diet that includes carbohydrates, proteins and lipids.

So pause the video now, come back to me when you're ready, and take your time.

Okay, so let's see what you've managed to put together for these tasks.

So for task one of naming the parts that lipids are formed from and drawing a diagram to demonstrate, you might have said that lipids are made from fatty acids and glycerol, and that lipids can have one glycerol and three fatty acids, or one glycerol and two fatty acids, and then drawn a diagram to show that.

So I've drawn one with three fatty acid chains, but you might have drawn one with two fatty acid chains.

For part two, I wanted you to list a number of functions of lipids and explain why they're important.

So you might have included comments about cell membranes, that they're important for forming the boundary of the cell for storing energy so that it's available for when needed later for respiration.

And their functions within thermal insulation, to help keep the organism warm.

And for protection, such as around vital organs, to protect essential and delicate parts of the organism's body.

Again, just review your answer before we move on.

And then, in the third part to this task, I wanted you to state three sources of lipids and then explain why it's important to have a balanced diet that includes carbs, proteins, and lipids.

So you might have initially said that lipids are found in things like oily fish, nuts, seeds, cheese, butter, other dairy products, oily vegetables, avocados, for instance, that sort of thing.

Maybe some or all of those ideas that you've put down.

And then about having a balanced diet that's important.

And a balanced diet includes carbohydrates, proteins, and lipids because they all provide essential molecules that are required for a healthy lifestyle and numerous functions.

And you might have listed some of those, such as storing energy, providing energy for movement, providing the building blocks so that we can build our body and keep it running in order.

Various different functions of proteins, for instance.

So again, check over your work, make sure that you've got all the relevant key bits and bobs.

I'm sure you've added much more detail than I have there.

Excellent job.

Well done indeed.

Okay, so thank you very much for joining me in today's lesson.

We have today covered the fact that organisms are made up of many different types of molecules, but they are grouped into specific categories, including carbohydrates, proteins, and lipids.

There are other molecules that are required, including water and minerals as well.

We've seen that carbohydrates, proteins, and lipids are all really important to building the cells and the subcellular structures that make up the organism and the parts that our organism is made from.

And that these molecules are ultimately large polymers.

They're complicated units which are made of much smaller repeated units.

So carbohydrates are made from repeated sugar units.

Proteins are made from repeated amino acid units.

And lipids are made from repeated units of fatty acids and glycerol.

So I hope you've enjoyed today's lesson and that you've learned a lot.

Thank you very much for joining me indeed, and I hope to see you again soon.

Bye.