Carbohydrates - Video Tutorials & Practice Problems
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Carbohydrates
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In this video, we're going to do a quick review on carbohydrates. So recall that carbohydrates are also known as saccharides, and carbohydrates are sugars that are made up of carbon, hydrogen, and oxygen atoms, and a ratio of c n to h two o n, where there are certain number of water molecules hydrating a certain number of carbon atoms. And we can see that in the root of carbohydrates where carbo refers to the carbons and hydrates refers to the water molecules hydrating those carbons. And so, if we mathematically distribute this little n over here, we can rewrite this chemical formula as c n H2n0n, where there are double the amount of hydrogen atoms than there are either carbon or oxygen atoms. And this is relevant because the chemical formulas of, carbohydrates can be written in either format, and it's important to be able to recognize this. And so recall that monosaccharides are, the monomers of carbohydrates. And so monosaccharides tend to be water soluble white crystalline solids with a sweet taste, and that's exactly how we know our sugars to be. And carbohydrates can be used, for lots of different functions, but carbohydrates can serve as a primary short term energy source in pretty much every living organism. Now, monosaccharides can be repetitively linked together to create a polysaccharide polymer. So in our example below, what we'll see is that we have these monosaccharides listed on the left over here, and these are monosaccharide monomers. Monomers. And through a process, we can link these monosaccharide monomers together covalently to create a polysaccharide polymer. And unlike nucleic acids and proteins, polysaccharides do not have directionality. And notice that the ending o s e on a word is indicative that it is a sugar. So a, glucose, fructose, sucrose, etcetera, all end in o s e, and they are all sugars and carbohydrates. And so in the next video, what we're gonna do is talk about the monosaccharide glucose. And so I'll see you guys in that video.
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Monosaccharides
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So now that we've refreshed our memories that monosaccharides are the monomers of carbohydrates and can be linked together to form polysaccharides, we can talk about the monosaccharide itself. And most monosaccharides contain several hydroxyl groups. And recall that a hydroxyl group is a functional group that consists of an oxygen atom bounded to a hydrogen atom. And, because monosaccharides contain several hydroxyl groups, they are known as polyalcohols, where an alcohol is a molecule that contains a hydroxyl group. And recall that glucose has a chemical formula of c 6h1206, and glucose is a monosaccharide. And it is actually the most abundant hex ose, where hexose ends in o s e, so it's definitely a carbohydrate, and the hex part refers to the fact that it has 6 carbons. And glucose can be used by pretty much every living organism, either as a source of fuel or to build structures. And glucose monomers can be linked together via what are known as glycosidic bonds. So let's take a look at an example. And down here, what we'll see is that we have a glucose molecule with the chemical formula c 6 h 1206. And glucose can take 2 different forms. It can take a linear form or a cyclic form. And in both forms, what we'll see is that we have all of these hydroxyl groups, and therefore, it is a polyalcohol. And glucose monomers can be linked together via glycosidic bonds, and we can see that over here, where each of these pink bonds represent a glycosidic bond that links one glucose monosaccharide to the next. And so when we link, monosaccharides in this fashion, we create a polysaccharide. And that transitions us perfectly into our next video where we're gonna talk about different types of polysaccharides.
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Polysaccharides
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So examples of polysaccharides include starch, glycogen, cellulose, peptidoglycan, and chitin. And all of these are polysaccharides that vary in their functions, and we'll talk about their functions down in the chart below. Now carbohydrates are quite interesting because they can be covalently linked to other macromolecules such as proteins to create glycoproteins, lipids to create glycolipids, and nucleic acids to create nucleotides. And so down here in our chart, what we're gonna do is fill in the function of each polysaccharide that's listed in the left hand column. And And so recall that starch is used as energy storage in plants, whereas glycogen is used as energy storage in animals. Now you may have learned that cellulose is a predominant component of plant cell walls, whereas peptid hard shells of, insects as well as crabs, and it's a predominant component in the cell wall of fungi. And so what you can see is that we have different, structural polysaccharides that have similar functions but in different organisms. And you can also see that the first two are energy storage polysaccharides, whereas the bottom 3 are more so structural polysaccharides. And so over here in the right side image, what we have is a glycoprotein. And the glycoprotein consists of a carbohydrate portion shown in gray and a protein portion shown in light blue. And this carbohydrate portion has a chain and a secondary chain that branches off of the chain, and carbohydrates tend to make these complex structures with lots of branching. And, they don't have to, but they can. And so the glycoprotein here consists of the carbohydrate as well as the protein portion. Now in a similar fashion, we have a glycolipid over here, which contains a carbohydrate portion in gray, and it also includes the phospholipid itself. Now down below, we have a DNA nucleotide. And what we can see is that it has a pentose sugar, specifically a deoxyribose pentose sugar. And so carbohydrates or, these pentose sugars here are an important component of all nucleotides, and therefore, a very crucial impo component to all, nucleic acids. And so we'll talk a lot more about carbohydrates as we move forward in our biochemistry course. And I'll see you guys in the practice problem videos.
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Problem
Problem
Which of the following expresses the correct chemical formula of a carbohydrate?