The Macromolecules of Life 1

by Georgina Cornwall, PhD

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    00:01 ?Previously, you’ve learned about atomic structure and how atoms come together to form molecules and all of that’s based on electrons in the valence shell.

    00:11 Now, we’re going to venture into exploring how these smaller molecules come together to form the four major classes of macromolecules or biological molecules.

    00:25 So in this lecture you’ll learn to identify what the monomers and polymers are of the four classes of macromolecules, as well as explain the process of dehydration synthesis; that is how these molecules come together.

    00:42 And you’ll also be able to identify carbohydrate molecule structure and discuss why we can’t eat grass.

    00:52 So let’s begin by taking a look at how macromolecules come together.

    00:58 All organic macromolecules are composed of hydrocarbon chains with additional functional groups.

    01:06 By hydrocarbon we mean simply hydrogens and carbons covalently bonded to each other.

    01:12 In this example, you can see the hydrogen carbons in black and white and then a functional group on the far end of that molecule.

    01:22 This one’s myristic acid but that doesn’t really matter at the moment.

    01:26 The point here is you can see that there are single covalent bonds between each of the carbon molecules in that chain and they are fully saturated; they’re covered in hydrogens.

    01:39 In this case the chain is straight.

    01:41 On occasion, you’ll see that the chain has kinks in it and that might be because of double bonds between the carbons, but either way it’s a carbon hydrogen chain with functional group on the end.

    01:53 We’ll discuss those functional groups shortly.

    01:56 Here’s the comparison of those three molecules again.

    01:58 Each of them the point here being that they have a hydrocarbon chain with functional groups added to the basic structure of the hydrocarbon chain.

    02:08 Now, we’re going to be looking at a variety of different functional groups.

    02:14 Here are some of the main ones that we’ll see in biology.

    02:18 First of all, we have the hydroxol group that I previously introduced.

    02:22 It’s simply an OH.

    02:23 We’ll see that in a lot of carbohydrates, proteins, nucleic acids and lipids, so in all four classes of macromolecules.

    02:31 We also will see the carbonyl group which we’ll see on carbohydrates and nucleic acids.

    02:38 We can also see the carboxyl group in proteins and lipids.

    02:42 We will see amino group, again, in proteins and we will see sulfhydryl on occasion in proteins where we create disulfide bridges and protein folding and phosphate groups in nucleic acids.

    02:58 Methyl groups we’ll see in proteins and in DNA.

    03:03 Before we begin our discussion of the various macromolecules, we need to understand two major terms.

    03:10 The first of which is monomer and the other is polymer.

    03:13 Mono means single, -mer means units, so monomers are single units that are strong together to form polymers, multiple units.

    03:24 So here we have a bunch of monomers; so for example glucose molecules.

    03:29 Glucose molecules are polymerized or brought together to a process called dehydration synthesis, that we’ll investigate shortly, and they will form a polymer strands, so many units of glucose.

    03:44 In this case it could be glycogen for example.

    03:47 So let’s look briefly at each of the four classes of macromolecules so that I can introduce them to you and later we’ll explore them in a much more depth.

    04:00 First of all, we look at carbohydrates.

    04:02 Carbohydrates are long chain sugars, often they could be single sugars or they could be disaccharides or polysaccharides.

    04:13 The monomer is a monosaccharide, in this case glucose.

    04:19 Multiple glucoses are strong together to form a starch or many different forms of polysaccharides.

    04:28 Then let’s look at the basics of polypeptides or proteins.

    04:34 Polypeptides are strings of amino acids.

    04:37 The monomer being the amino acid, the polymer being the whole polypeptide, the string of amino acids.

    04:45 Now the polypeptide will fold and form eventually its protein, but we’ll cover that in much more detail in the following lecture.

    04:54 A brief look at nucleic acids.

    04:59 We see that the polymer is the DNA strand or the RNA strand and that polymer is composed of multiple repeating subunits of a monomer, which in this case is the nucleotide.

    05:13 The nucleotide is composed of three subunits itself but we’ll deal with them in much more detail, again, in the following lecture.

    05:21 Lipids are a little bit different because they are non-polymer macromolecules, which means they don’t have repeating subunits of exactly the same type of thing.

    05:33 For example, amino acids or glucose molecules or monosaccharides.

    05:39 In this case, we have three fatty acid tails tied together by one glycerol molecule so it’s not a repeating thing so lipids are a class of non-polymer macromolecules.

    05:57 The other three classes are polymer macromolecules, we have monosaccharides linking together to form polysaccharides, amino acids to form polypeptides, nucleic acids are formed by monomers of nucleotides.

    06:14 So then we’ll move on into looking at how these come together? Macromolecules are all stuck together with our friend, the covalent bond.

    06:25 What happens here is we remove a hydrogen from one end of the molecule and a hydroxide from the other end of the next molecule, the next monomer, and we extract H2O and those two molecules will bind together.

    06:44 They now have enough an affinity to pair electrons with each other.

    06:48 So because we’re losing water this is called dehydration synthesis.

    06:53 So two monomers will come together through polymerization reaction, polymer-ization, where we lose water and that creates the affinity between the two monomers to form a covalent bond.

    07:08 And again, the covalent bonds are the strongest bonds that we see; single, double and clearly triple, the most strong bond that we’ll see in biology.

    07:20 On the other hand, when we metabolize polymer macromolecules, for example in the metabolism of say pasta, a complex carbohydrate, we’re going to separate the monomers from each other in a process called hydrolysis, hydro-lysis, so we’re breaking apart the water molecule.

    07:41 We’ll put hydrogen on one end of a monomer and a hydroxide group on the other end of the monomer and now they’re free to separate and that covalent bond is broken between the monomers.

    07:55 So contrasting reactions that we see are the hydrolysis reaction, breaking things apart, and dehydration synthesis is bringing things together.

    08:07 So now that we have an understanding of how things come together, how are monomers joined together to form polymers is the same with every class of macromolecules.

    08:17 Let’s dig a little bit deeper into carbohydrates.

    08:20 Carbohydrates are molecules that are composed of monomers or monosaccharides.

    08:27 Monosaccharides are simple sugars.

    08:30 They come in a form of either 3 carbon sugars.

    08:33 There’s our carbon backbone that got hydrogen associated with it.

    08:38 They could come in the form of 5 carbon sugars, we’ll see this when we look at ribose and deoxyribose in the structure of DNA, and then we could have 6 carbon sugars.

    08:49 Ones we’re familiar with are things like glucose and fructose and galactose.

    08:53 These monomers can all come together to form polymer macromolecules.

    08:59 We could have disaccharides or trisaccharides, but mostly we deal with disaccharides which are two sugars coming together or polysaccharides which are multiple sugar units coming together.

    09:12 In the case of disaccharides, we could look at something like glucose.

    09:18 Glucose is a chain of 6 carbon atoms associated with their hydrogen, so those are hydrocarbons.

    09:27 Now that molecule can fold in solution.

    09:31 It does fold into a ring structure where we see the terminal oxygen bind with the number 5 carbon in order to form that ring.

    09:42 Now, something that we’ll come to later on is that this could form in two different ways.

    09:48 It can either fold in this direction and form alpha-glucose or it could fold in that direction and form beta-glucose.

    09:56 The result here is that we have either an H group up and OH group down or an OH group up and an H group down and that is going to impact how these two molecules come together.

    10:12 Again, we can see that there are multiple forms of C6H12O6.

    10:20 Not only could they fold in a different direction to form the ring, but they could also be a slightly different structural shape.

    10:29 So we have the basic formula, C6H12O6.

    10:33 They all have the same number of carbons, hydrogens and oxygens, however, they could form a different arrangement with those carbons, hydrogens and oxygens.

    10:44 We can have a structural isomer which is structurally quite different.

    10:49 You can see here that we have a carbon oxygen double bond replacing one of the single bonds in which case it’s quite a different molecule.

    10:58 Or we can have a stereo isomer in which one piece might be just reflected and it could be at any one of those carbons.

    11:06 The point here is that this different structure will require a different enzyme to hydrolyze or break the sugar apart, so each of these has a very specific fit to that certain enzyme that’s responsible for breaking them down or even putting them together.

    11:26 So disaccharides are just two sugars together and they’re generally responsible for storage and transport both within an organism and between different organisms.

    11:42 So we could consume a disaccharide, for example, by consuming something like lactose.

    11:49 So here let’s look at alpha-glucose and dehydration synthesis forming alpha-glucoses together.

    11:58 This is just one way the chain could form; we look at alpha versus beta-glucose.

    12:02 And we could have alpha-glucose linked to fructose and we come up with a disaccharide that’s called sucrose.

    12:12 Here, dehydration synthesis we lose an O from one end and OH from the other and they come together to form the disaccharide sucrose.

    12:21 Lactose is a disaccharide that provides a great example of enzyme specificity.

    12:26 There are two sugar monomers in there that we produce an enzyme for during our lactation years when we’re feeding on milk up until about two years of age and in adulthood, unless we’re exposed to a diet very high in milk.

    12:44 Generally, we don’t produce the enzyme lactase that breaks down lactose.

    12:49 So that’s just an example of how the enzymes can be very specific to the type of sugar or the isomer of sugar that’s involved in a polymer.

    13:02 This is the case for many polymers whether we’re looking at proteins or nucleic acids or lipids for that matter.

    13:10 So polysaccharides are more than two sugar monomers.

    13:16 So more than two monomers of sugar strung together could form starch or glycogen or chitin for that matter.

    13:23 Here’s an example of glycogen, a storage polysaccharide that we see in our muscle cells.

    13:31 This is how we store glucose, comes into the blood, we pack it away and store it as glycogen in the muscles or in the liver.

    13:38 We could also see amylose or amylopectin.

    13:41 This is a storage polysaccharide that we see in plants.

    13:45 Cellulose is also a linear chain of glucose molecules strung together.

    13:52 So the question is then why is it that we couldn’t eat grass like a cow could? Again, it comes down to enzyme specificity and this isomerization issue.

    14:03 This is an isomer molecule where we see not the alpha-glycosidic linkage or the alpha form of the molecule, we see beta-glucose where the OH and H group are reversed.

    14:17 And this is a beta-1, 4 glycosidic linkage and we don’t contain any enzymes ever in our life to break down this polysaccharide.

    14:27 So cows actually have bacteria in their gut that help them break down these bonds.

    14:33 They have the bacteria have the enzymes that break down the beta-glycosidic linkage so that cows can actually then break down the carbon chains and release energy and make ATP and live off of that ATP.

    14:45 An example of a structural polysaccharide would be chitin.

    14:51 Chitin is found in the shells of lobsters and crabs and shrimp and it’s made of a chain of glucose molecules that are cross-linked with proteins to give it much more integrity and strength.

    15:02 Again, we couldn’t eat the shell of a lobster or crab or you could try but it wouldn’t be so good.

    15:08 So the take home message here about the group of polysaccharides is that the monomer is called monosaccharide, the polymer is a polysaccharide no matter which storage form or structural form it is and the linkage between them is by dehydration synthesis but it’s called a glycosidic linkage because it is in carbohydrates.

    15:37 So carbohydrates have a monomer, a polymer and a linkage and for each of the macromolecules we’re going to discuss the monomer, the polymer and the linkage form between them.

    15:49 So hopefully from this lecture you’ve had a nice introduction to each of the macromolecules that we’re going to cover.

    15:57 What their monomers and what their polymers are called? And you could explain the process of dehydration synthesis; how each of the monomers are held together? As well as identify some carbohydrate structures like glycogen and amylopectin and chitin and discuss precisely why you can’t eat grass to your friends.

    16:21 Thank you so much for joining me for this lecture.

    16:24 I hope to see you in the next one shortly.

    About the Lecture

    The lecture The Macromolecules of Life 1 by Georgina Cornwall, PhD is from the course The Macromolecules of Life. It contains the following chapters:

    • How macromolecules come together
    • Hydrolysis Reactions
    • Glucose
    • Polysaccharides

    Included Quiz Questions

    1. C and H
    2. C and N
    3. C and S
    4. C and P
    5. C and He
    1. Carbohydrates, Proteins, Nucleic acids and Lipids
    2. Alcohols, Esters, Ketones, and Hydrocarbons
    3. Oleic acid, Lactose, Nucleotides, and Peptides
    4. Starch, DNA, RNA, and Enzymes
    5. Glycogen, Starch, Linoleic acid and RNA
    1. Phosphate group ----- Carbohydrates
    2. Sulfhydryl group ----- Proteins
    3. Phosphate group ----- Nucleic acids
    4. Amino group ----- Proteins
    5. Hydroxyl group ----- Carbohydrates
    1. Amino acid ---- Lipids
    2. Nucleotide ---- Nucleic acids
    3. Glucose ---- Starch
    4. Amino acid ---- Proteins
    5. Glucose ---- Glycogen
    1. Lipids are polymeric macromolecules composed of repeated units of palmitic acid molecules
    2. Lipids are non-polymer macromolecules
    3. Lipids are an important part of the cellular membrane structure
    4. Myristic acid, palmitic acid, oleic acid, linoleic acid and linolenic acid are predominant fatty acids in the mammalian lipids
    5. Lipids consist of three fatty acid tails tied together with one glycerol molecule
    1. …a dehydration or polymerization reaction to create a polymer.
    2. …a hydrolysis reaction to break the heavy units of a polymer
    3. …a depolymerization reaction
    4. …an oxidation reaction
    5. …a hydration process
    1. The dehydration synthesis process occurring in the living cells is a perfect example of polymerization
    2. During catabolism, the polymer macromolecule is broken down into the monomer units
    3. The catabolic reactions are the energy generating reactions
    4. Cellular respiration falls under the category of catabolic reactions
    5. In catabolic reactions, the hydrolysis of water facilitates the depolymerization of polysaccharides
    1. …energy storage molecules and structural components of cellular structures
    2. …enzymes in metabolic reactions
    3. …they form protein molecules after polymerization
    4. …they get covalently attached to glycerol molecule to form lipid molecules
    5. …they facilitate the protein synthesis by acting as an enzyme
    1. Fructose ----- Disaccharide sugar
    2. Glyceraldehyde ----- Simplest monosaccharide
    3. Ribose ----- 5-Carbon sugar
    4. Deoxyribose ----- Nucleic acid component
    5. Glucose ----- Primary cell fuel
    1. Glucose is the only sugar which is represented by the molecular formula C6H12O6
    2. Fructose and glucose monosaccharides are structural isomers of each other
    3. Glucose and glycogen act as primary cell fuel and energy storage molecules in the living cells
    4. Glucose can polymerize with itself or other monosaccharides to form di-, tri- and polysaccharide molecules
    5. Glucose and galactose are two stereoisomers sharing their molecular formula with each other
    1. …a glycosidic bond during the dehydration synthesis
    2. …a polypeptide bond during the hydration process
    3. …a phosphodiester bond during the integration process
    4. …an ionic bond during the nucleophilic attack of protons
    5. …a hydrogen bond during the dehydration synthesis process
    1. Cellobiose ---- Galactose and Galactose
    2. Sucrose ---- Glucose and Fructose
    3. Lactose ---- Galactose and Glucose
    4. Maltose ---- Glucose and Glucose
    5. Trehalose ---- Glucose and Glucose
    1. …composed of glucose and galactose and is specifically broken down by the enzyme lactase
    2. …composed of glucose and sucrose and is non-specifically broken down by protease enzymes
    3. …composed of galactose and sucrose and is non-specifically broken down by protease enzymes
    4. …composed of maltose and sucrose and is specifically broken down by lactase enzymes
    5. …composed of two galactose units and is specifically broken down by protease enzymes
    1. Hydrolysis, dehydration synthesis
    2. dehydration synthesis, hydrolysis
    1. monosaccharides, covalent bonds called glycosidic linkages
    2. monosaccharides, ionic bonds called glycosidic linkages
    3. glycerol, linked by covalent bonds called glycosidic linkages
    4. glycerol linked by ionic bonds called glycosidic linkages
    1. We do not have the enzyme necessary to break the Beta 1,4 glycosidic linkage that holds the individual glucose molecules together
    2. We could, it just doesn't have a great texture
    3. In adulthood we no longer produce the enzymes necessary to break the Beta 1,4 glycosidic linkage that holds the individual glucose molecules together
    1. Glycogen is a structural polysaccharide which provides strength to the algal cell walls
    2. Glycogen acts as an energy storage molecule in the liver and muscles of human beings
    3. Glycogen is highly complex and branched polymer of glucose
    4. Glycogen is composed of α-glucose units joined by α (1→4) glycosidic bonds and α (1→6) glycosidic bonds at branched points
    5. During exercise, the glycogen stored in skeleton muscles is utilized to produce energy
    1. …β (1→4) glycosidic bonds
    2. … α (1→4) glycosidic bonds
    3. …α (1→6) glycosidic bonds
    4. …β (1→6) glycosidic bonds
    5. …β (1→1) glycosidic bonds
    1. Cellulose helps in the smooth functioning of the intestinal track by acting as fiber
    2. Cellulose helps in the secretion of gastric juices by stimulating the gastric glands
    3. Cellulose aids in the secretion of intestinal enzymes by stimulating the intestinal glands
    4. Cellulose acts as a cofactor to activate the salivary amylase
    5. Cellulose acts as a stimulator to start the flow of bile from the gall bladder.
    1. Human gastric enzymes can easily break down chitin into glucose units
    2. Chitin is a polymer of a glucose derivative known as N-acetylglucosamine
    3. Chitin is a primary component of exoskeletons of crustaceans like crabs, lobsters, and shrimp
    4. Humans cannot digest chitin due to the lack of specific digestive enzymes
    5. Chitin provides strength and integrity to the cell wall of fungal cell walls

    Author of lecture The Macromolecules of Life 1

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD

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