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Questions and Answers
What is the empirical formula for a monosaccharide with six carbon atoms?
What is the empirical formula for a monosaccharide with six carbon atoms?
How many possible stereoisomers exist for a six-carbon aldose?
How many possible stereoisomers exist for a six-carbon aldose?
Which of the following is NOT a function of carbohydrates in biological systems?
Which of the following is NOT a function of carbohydrates in biological systems?
Which of the following is an example of a disaccharide?
Which of the following is an example of a disaccharide?
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What distinguishes an aldose from a ketose?
What distinguishes an aldose from a ketose?
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Which of the following is NOT a characteristic of monosaccharides?
Which of the following is NOT a characteristic of monosaccharides?
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What type of carbohydrate is composed of a few monosaccharides covalently linked together?
What type of carbohydrate is composed of a few monosaccharides covalently linked together?
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Which of the following is NOT a type of polysaccharide?
Which of the following is NOT a type of polysaccharide?
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What is the name of the 6-membered ring formed by the cyclization of glucose?
What is the name of the 6-membered ring formed by the cyclization of glucose?
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Which of the following are true about epimers?
Which of the following are true about epimers?
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What is the difference between α and β anomers?
What is the difference between α and β anomers?
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Which of the following is NOT a characteristic of optical isomers?
Which of the following is NOT a characteristic of optical isomers?
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Which type of sugar is formed when a ketone reacts with an alcohol?
Which type of sugar is formed when a ketone reacts with an alcohol?
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What does the D or L designation in carbohydrates refer to?
What does the D or L designation in carbohydrates refer to?
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What is a racemic mixture?
What is a racemic mixture?
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Which of the following statements is TRUE about Haworth projections?
Which of the following statements is TRUE about Haworth projections?
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What is a primary role of chondroitin in the body?
What is a primary role of chondroitin in the body?
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In what context is heparin primarily used?
In what context is heparin primarily used?
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Which type of lectin is known to be involved in cell adhesion and recognition?
Which type of lectin is known to be involved in cell adhesion and recognition?
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What is a characteristic of lectins?
What is a characteristic of lectins?
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Which of the following organisms produce lectins?
Which of the following organisms produce lectins?
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What type of linkage is responsible for the branching of glycogen?
What type of linkage is responsible for the branching of glycogen?
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Which of the following statements about cellulose is correct?
Which of the following statements about cellulose is correct?
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What is chitin primarily used for in commercial applications?
What is chitin primarily used for in commercial applications?
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Which type of glycoprotein contains predominantly carbohydrates by weight?
Which type of glycoprotein contains predominantly carbohydrates by weight?
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What is a distinctive feature of proteoglycans?
What is a distinctive feature of proteoglycans?
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Which of the following best describes the structure of cellulose?
Which of the following best describes the structure of cellulose?
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What type of bond is formed when two monosaccharides react and release water?
What type of bond is formed when two monosaccharides react and release water?
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What is the primary role of glycoproteins in biological systems?
What is the primary role of glycoproteins in biological systems?
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What distinguishes microcrystalline cellulose from other forms of cellulose?
What distinguishes microcrystalline cellulose from other forms of cellulose?
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Which disaccharide is produced from two α-D-glucose molecules?
Which disaccharide is produced from two α-D-glucose molecules?
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Which disaccharide has a β(1→4) linkage and is commonly found in milk?
Which disaccharide has a β(1→4) linkage and is commonly found in milk?
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What is the primary role of maltose in food processing?
What is the primary role of maltose in food processing?
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Which sugar is commonly known as table sugar and derived from sugarcane?
Which sugar is commonly known as table sugar and derived from sugarcane?
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What happens to sucrose when it is hydrolyzed by the enzyme sucrase?
What happens to sucrose when it is hydrolyzed by the enzyme sucrase?
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Which vitamin resembles a monosaccharide and is water-soluble?
Which vitamin resembles a monosaccharide and is water-soluble?
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What characterizes lactose intolerance in humans?
What characterizes lactose intolerance in humans?
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What compounds are formed when carbohydrates react with phenylhydrazine?
What compounds are formed when carbohydrates react with phenylhydrazine?
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Which disaccharide forms a powder puff-shaped osazone?
Which disaccharide forms a powder puff-shaped osazone?
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What is the net reaction of glucose fermentation?
What is the net reaction of glucose fermentation?
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What type of sugar is produced by the oxidation of the aldehyde group in monosaccharides?
What type of sugar is produced by the oxidation of the aldehyde group in monosaccharides?
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Which of the following is a procedure for ester formation in monosaccharides?
Which of the following is a procedure for ester formation in monosaccharides?
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Which type of sugar is created through the reduction of aldoses?
Which type of sugar is created through the reduction of aldoses?
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What do D-fructose and D-mannose produce when reacted with phenylhydrazine?
What do D-fructose and D-mannose produce when reacted with phenylhydrazine?
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Which of the following is an example of an alditol derived from a monosaccharide?
Which of the following is an example of an alditol derived from a monosaccharide?
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Study Notes
Carbohydrates: General Characteristics
- Carbohydrates are polyhydroxy aldehydes or ketones, and their derivatives.
- The term 'carbohydrate' comes from the French term 'hydrate de carbone'.
- Carbohydrates are composed of carbon (C), hydrogen (H), and oxygen (O).
- The empirical formula for carbohydrates is (CH₂O)ₙ.
- Not all carbohydrates follow this formula (e.g., deoxysugars and aminosugars).
- Carbohydrates are the most abundant compounds in nature. Cellulose, for example, accounts for approximately 100 billion tons annually.
Functions of Carbohydrates
- Source of energy.
- Involved in the biosynthesis of other biochemical entities (e.g., fats, proteins).
- Associated with other entities such as glycosides, vitamins, and antibiotics.
- Component of structural tissues in plants (e.g., cellulose) and microorganisms (e.g., lignin, murein)
- Involved in biological transport.
- Support cell-cell recognition.
- Part of the activation of growth factors.
- Important in immune system modulation.
Carbohydrates (Glycans) Composition
- Basic composition: (CH₂O)ₙ or H-C-OH.
- Monosaccharides: Simple sugars with multiple hydroxyl (OH) groups. Categories based on the number of carbons include trioses, tetroses, pentoses, and hexoses (3, 4, 5, 6 carbons respectively).
- Disaccharides: Two monosaccharides covalently linked.
- Oligosaccharides: A few monosaccharides (up to 9-10) covalently linked.
- Polysaccharides: Polymers consisting of monosaccharide or disaccharide units. Subdivided into homopolysaccharides (e.g., starch), heteropolysaccharides, and complex carbohydrates.
Monosaccharides
- Empirical formula: Cₙ(H₂O)ₙ.
- Exist in both open-chain and ring structures.
- Exhibit multiple structural isomers.
- Chiral carbon atoms lead to optical isomers.
- Typically have 3 to 6 carbon atoms.
- Common monosaccharides include pentoses (5-carbon sugars) and hexoses (6-carbon sugars).
- Monosaccharide chains have at least one carbonyl group (C=O).
- Aldoses have the carbonyl group at the end of the chain.
- Ketoses have the carbonyl group within the chain.
- Common examples include D-glucose and D-fructose.
Diagram of Isomeric Forms of Carbohydrates
- Isomers: Molecules with the same molecular formula but different structures.
- Constitutional isomers: Differ in the order of attachment of atoms.
- Stereoisomers: Atoms are connected in the same order, but differ in spatial arrangement.
- Enantiomers: Nonsuperimposable mirror images.
- Diastereoisomers: Not mirror images.
- Epimers: Differ at one of several asymmetric carbon atoms.
- Anomers: Differ at the anomeric carbon (the carbon that was involved in the cyclization).
Stereoisomers: D and L Forms
- D (dextrorotatory) and L (levorotatory) designate optical isomers based on configuration around the asymmetric carbon in glyceraldehyde.
- For sugars with more than one chiral center, D and L refer to the asymmetric carbon (often C5) furthest from the aldehyde or ketone group.
- Most naturally occurring sugars are D-isomers.
Optical Isomerism
- Property exhibited when mirror images of a molecule are non-superimposable.
- Asymmetric compounds rotate plane-polarized light.
- Measured using a polarimeter.
- Rotation can be dextrorotatory (+) or levorotatory (-).
- A racemic mixture (DL mixture) contains equal amounts of D and L isomers and does not exhibit optical activity.
Enantiomers and Epimers
- Enantiomers are nonsuperimposable mirror images.
- Epimers differ at only one asymmetric carbon atom.
Hemiacetal and Hemiketal Formation
- Aldehydes react with alcohols to form hemiacetals.
- Ketones react with alcohols to form hemiketals.
- Monosaccharides can cyclize via hemiacetal or hemiketal formation.
- Cyclization produces ring structures (e.g., pyranose, furanose) which create new asymmetric (chiral) centers, the anomeric carbon.
- Haworth projections depict the cyclic structure of sugars.
Mutarotation
- α and β anomers readily interconvert in solution through an open-chain intermediate.
Reactions of Monosaccharides: Action of Base on Sugars
- Sugars are weak acids forming salts in high pH.
- Formation of a 1,2-enediol intermediate.
- The Lobry de Bruyn-Alberta von Eckenstein reaction is a reversible isomerization of monosaccharides in alkaline solution.
- Enediols are highly reactive, making sugars powerful reducing agents in alkaline environments.
Reactions of Monosaccharides: Action of Base on Sugars
- Reducing sugars react with oxidizing agents (e.g., Cu²⁺) and form a precipitate.
- Copper sulfate is a common oxidizing agent.
- The reduction of the copper ion indicates an aldehyde group oxidation, signifying a reducing sugar.
- Examples include Fehling's solution and Benedict's solution, used to test for reducing sugars.
Oxidation Reactions
- Aldoses can oxidize into 3 types of acids: aldonic acids, uronic acids, and saccharic acids.
- The aldehyde group can be oxidized to a carboxylic acid group (producing aldonic acid).
- The primary alcohol group can be oxidized whilst preserving the aldehyde group, forming uronic acids.
- Oxidizing both ends creates saccharic acids, also known as glucosaccharic acid when glucose is the reacting monosaccharide.
Reduction Reactions
- Reduction converts the carbonyl group (-CHO or >C=O) to an alcohol group (-CH₂OH).
- The result is an alditol or a sugar alcohol. Examples of alditols include sorbitol and mannitol.
Dehydration: Action of Strong Acids on Monosaccharides
- Strong acids dehydrate monosaccharides.
- D-ribose, under heat and concentrated sulfuric acid, gives furfural.
- D-Glucose forms 5-hydroxymethyl furfural under similar conditions.
- The furfurals react with reagents like -naphthol, giving a characteristic purple color used for carbohydrate detection via the Molisch test.
Formation of Osazones
- Carbohydrates (monosaccharides) react with phenylhydrazine to create osazones.
- This reaction involves the aldehyde group.
- The product is a crystalline compound.
- This method was once used for identifying different sugars. Now, it is seldom utilized, replaced by more sensitive methods like HPLC.
Formation of Esters
- Several important sugar esters are involved in cellular metabolism.
- The alcohol groups of monosaccharides can be esterified through enzymatic and non-enzymatic reactions.
- The phosphate moiety is often donated by ATP.
Fermentation
- Fermentation is an energy-yielding metabolic pathway that doesn't change the oxidation state.
- Yeast uses glucose, fructose, or maltose to generate pyruvate which is converted to ethanol and CO₂.
Derivatives of Monosaccharides
- Sugar acids: Formed by oxidizing the aldehyde or primary alcohol group in a monosaccharide (e.g., gluconic acid).
- Sugar alcohols (alditols): Formed by reducing aldoses or ketoses, including examples like sorbitol and mannitol.
- Amino sugars: Hydroxyl groups in monosaccharides are replaced by amino groups.
- Deoxysugars: Sugars with one less oxygen atom than the parent molecule, such as deoxyribose.
- Vitamin C (ascorbic acid): A water-soluble vitamin.
Glycosidic Bonds
- Anomeric hydroxyl groups join two sugars by removing a water molecule to form a glycosidic bond.
- The link forms a disaccharide.
- Examples include maltose, formed by two glucose molecules.
Disaccharides
- Formed when two monosaccharides link via a glycosidic bond.
- The specific glycosidic bond distinguishes different disaccharides (e.g., maltose has an α(1→4) glycosidic bond).
- When hydrolyzed (e.g. with acids or enzymes), they yield their component monosaccharides.
Maltose
- Formed from two α-D-glucose molecules linked by an α(1→4) glycosidic bond—known as malt sugar.
- Produced during the partial hydrolysis of starch.
- Used as a nutrient and fermenting reagent.
- Related to isomaltose.
Lactose
- Composed of a β-D-galactose and an α-D-glucose molecule, linked by a β(1→4) glycosidic bond.
- Important for infants.
- Known as milk sugar.
Sucrose
- Formed from α-D-glucose and β-D-fructose linked by an α(1→2)β glycosidic bond.
- Called table sugar.
- Commercial sources are sugar cane and sugar beets.
Cellobiose
- Two glucose molecules joined by a β(1→4) glycosidic bond.
- Produced during partial hydrolysis of cellulose.
Polysaccharides
- Large polymers of monosaccharides.
- Homoglycans: Starch, cellulose, glycogen, and inulin.
- Heteroglycans: Gums, mucopolysaccharides.
Homopolysaccharides: Starch
- The most common storage polysaccharide in plants.
- Composed of amylose (10-30%) and amylopectin (70-90%) depending on the plant source.
- The chains vary in size, having different molecular weights.
- Major sources include rice, corn, wheat, potatoes, and cassava.
- Used as a binder in pharmaceuticals and tablets, and for numerous industrial applications.
Homopolysaccharides: Amylose and Amylopectin
- Amylose: Linear structure with α(1-4) glycosidic bonds.
- Amylopectin: Highly branched structure with α(1-4) and α(1-6) glycosidic bonds.
Homopolysaccharides: Dextrans
- Products from the reaction of glucose and transglucosidase from Leuconostoc mesenteroides.
- Used as plasma extenders, molecular sieves, in infant formula, and in dental plaques.
Homopolysaccharides: Inulin
- β(1→2) linked fructofuranoses — a linear polymer.
- Lower molecular weight than starch.
- Yields fructose upon hydrolysis and is used in diagnostic tests.
Homopolysaccharides: Glycogen
- Animal starch, a highly branched storage polysaccharide found in animal liver and muscle tissue.
- Composed of many glucose monomers linked by α(1→4) and α(1→6) glycosidic bonds.
- Staining with iodine gives red-violet color.
- Hydrolyzed by various enzymes, including amylases and glycogen phosphorylase.
Homopolysaccharides: Cellulose
- Polymer of β-D-glucose molecules linked via β(1-4) linkages.
- Structural polysaccharide, most abundant in nature.
- Not digested easily in most animals, but serves a crucial structural function.
- Cellulose is found in cotton, flax, and wood.
Products Obtained from Cellulose
- Microcrystalline cellulose: binder in tablets.
- Methylcellulose: suspending agent and laxative.
- Oxidized cellulose: hemostat.
- Sodium carboxymethyl cellulose: laxative.
- Cellulose acetate: used in rayon & enteric coatings.
- Nitrocellulose: explosive.
Homopolysaccharides: Chitin
- Second most abundant carbohydrate polymer.
- Structural polymer found in fungi and in the exoskeletons of crustaceans and insects.
- A derivative binds to iron and can act to slow meat rancidity.
Heteropolysaccharides: Glycoproteins & Proteoglycans
- Proteins with carbohydrate molecules attached.
- Glycoproteins: Proteins with carbohydrates attached; most abundant by weight.
- Proteoglycans: Proteins with chains of glycosaminoglycans (large polysaccharides). Play structural roles, lubrication, etc.
- Mucins or mucoproteins: Predominantly carbohydrates; play lubricating roles in body fluids.
Glycoaminoglycans
- Involved in extracellular functions (e.g., cartilage).
- Heparin: Important anticoagulant used in blood banks.
Lectins
- Glycoprotein that binds to specific oligosaccharides on cell surfaces.
- High specificity and moderate to high affinity.
- Found in all organisms (plants, animals, bacteria and viruses).
- Roles include cell-cell recognition, signaling, adhesion, immune response.
- Examples include certain plant lectins (e.g., concanavalin A), and animal lectins (e.g., mannan-binding lectin(MBL)).
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Description
Test your knowledge on the properties and classifications of carbohydrates, including monosaccharides, disaccharides, and polysaccharides. This quiz covers key concepts such as stereoisomers, anomers, and the structural features that distinguish different types of sugars. Perfect for students studying biochemistry or biology.
