Biochemistry: Cyclic Forms of Sugars
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Questions and Answers

What is the term used to describe the cyclic form of glucose with a six-membered ring?

  • Furanose
  • Pyranose (correct)
  • Hemiacetal
  • Hemiketal

    • Which of the following is NOT one of the three forms of D-glucose?

  • β-D-glucopyranose
  • Open-chain form
  • D-fructofuranose (correct)
  • α-D-glucopyranose

    • What type of reaction is involved in the formation of a hemiacetal?

  • Addition reaction (correct)
  • Elimination reaction
  • Substitution reaction
  • Oxidation reaction

    • What specific carbon atom in D-glucose is involved in the formation of the cyclic structure?

    <p>C1 (C)</p> Signup and view all the answers

    What is the difference between α-D-glucopyranose and β-D-glucopyranose?

    <p>The position of the hydroxyl group on C1 (C)</p> Signup and view all the answers

    What is the name of the projection used to represent the cyclic forms of sugars?

    <p>Haworth projection (A)</p> Signup and view all the answers

    Which of the following is a characteristic of the anomeric carbon in a cyclic sugar?

    <p>It is the carbon atom with the highest oxidation state (B)</p> Signup and view all the answers

    What is the major difference between the structures of glycogen and cellulose?

    <p>Glycogen is branched, while cellulose is linear (B)</p> Signup and view all the answers

    What is the name of the cyclic form of fructose?

    <p>Fructofuranose (D)</p> Signup and view all the answers

    What is the main difference between Hemiacetal formation and Hemiketal formation?

    <p>Hemiacetal formation involves an aldehyde, while hemiketal formation involves a ketone. (D)</p> Signup and view all the answers

    What distinguishes a D isomer from an L isomer in a monosaccharide?

    <p>The spatial orientation of the –H and –OH groups (C)</p> Signup and view all the answers

    Which of the following statements about epimers is correct?

    <p>Galactose and glucose are C-4 epimers. (C)</p> Signup and view all the answers

    What is an example of enantiomers in sugars?

    <p>D-sugar and L-sugar (B)</p> Signup and view all the answers

    Which set of sugars is considered isomers of each other?

    <p>Glucose and mannose (A)</p> Signup and view all the answers

    What role do racemases play in carbohydrate chemistry?

    <p>They interconvert L- and D- isomers. (C)</p> Signup and view all the answers

    What are the repeating units that make up chondroitin sulphates?

    <p>N-acetylgalactosamine and glucouronic acid (A)</p> Signup and view all the answers

    Which statement accurately describes heparin?

    <p>Heparin contains repeating units of sulphated glucosamine and sulphated glucouronic acid. (A)</p> Signup and view all the answers

    Which glycoprotein contains the highest percentage of carbohydrate?

    <p>Human gastric glycoprotein (mucins) (B)</p> Signup and view all the answers

    What role do membrane-bound glycoproteins play in cellular processes?

    <p>Cell surface recognition and antigenicity (D)</p> Signup and view all the answers

    Which of the following tissues predominantly contains chondroitin sulphates?

    <p>Skin and cartilage (A)</p> Signup and view all the answers

    What is the general formula for monosaccharides?

    <p>(CH2O)6 (A)</p> Signup and view all the answers

    Which carbohydrate serves as a structural component in the cell walls of many bacteria?

    <p>Peptidoglycan (C)</p> Signup and view all the answers

    Which of the following is a characteristic of disaccharides?

    <p>Formed from two monosaccharide units (A)</p> Signup and view all the answers

    What type of saccharide is raffinose classified as?

    <p>Oligosaccharide (B)</p> Signup and view all the answers

    Which of these is an example of a ketose monosaccharide?

    <p>Fructose (C)</p> Signup and view all the answers

    What is a key difference between homoglucans and heteroglucans?

    <p>Homoglucans consist only of glucose, while heteroglucans contain different monosaccharides. (B)</p> Signup and view all the answers

    What is the classification basis for monosaccharides when related to carbon atoms?

    <p>Based on the number of carbon atoms they contain (D)</p> Signup and view all the answers

    Which of the following is NOT a derived carbohydrate?

    <p>Starch (C)</p> Signup and view all the answers

    What type of bond forms between two monosaccharides to create a disaccharide?

    <p>Glycosidic bond (A)</p> Signup and view all the answers

    Which disaccharide is formed from two glucose molecules linked by a beta bond?

    <p>Cellobiose (C)</p> Signup and view all the answers

    What distinguishes sucrose from other disaccharides?

    <p>It has both anomeric carbon atoms bonded together. (D)</p> Signup and view all the answers

    Which of the following is NOT a characteristic of polysaccharides?

    <p>Tastes sweet (D)</p> Signup and view all the answers

    Which configuration describes maltose?

    <p>α(1→4) (D)</p> Signup and view all the answers

    How many units of saccharide does an oligosaccharide contain?

    <p>3 to 10 (A)</p> Signup and view all the answers

    Which disaccharide consists of galactose and glucose?

    <p>Lactose (D)</p> Signup and view all the answers

    Which of the following best describes homopolysaccharides?

    <p>Consists of one type of monosaccharide (C)</p> Signup and view all the answers

    What is the primary linkage responsible for connecting glucose residues within the linear chains of amylopectin?

    <p>α(1--&gt;4)-D-glucosidic bonds (C)</p> Signup and view all the answers

    Which enzyme is responsible for breaking down maltose into glucose?

    <p>Maltase (C)</p> Signup and view all the answers

    Why can't humans utilize cellulose as a source of glucose?

    <p>Humans lack the enzyme cellulase to break down the β-1,4-glucosidic linkages in cellulose. (B)</p> Signup and view all the answers

    What type of bond is found between the N-acetyl-D-glucosamine monomers in chitin?

    <p>β(1--&gt;4)-D-glucosidic bonds (C)</p> Signup and view all the answers

    Which of the following is NOT a non-carbohydrate structure that carbohydrates can be attached to by glycosidic bonds?

    <p>Amino acids (A)</p> Signup and view all the answers

    What type of glycosidic link is formed when a sugar is attached to an -OH group on a non-carbohydrate molecule?

    <p>O-glycosidic link (C)</p> Signup and view all the answers

    What is the primary characteristic that defines a heteropolysaccharide?

    <p>It is composed of different types of sugar monomers or their derivatives. (D)</p> Signup and view all the answers

    Which of the following is an example of a heteropolysaccharide (heteroglucan) based on the content provided?

    <p>None of the above (D)</p> Signup and view all the answers

    Flashcards

    D and L isomers

    Monosaccharides distinguished by the orientation of the –OH group.

    Isomers

    Compounds with the same formula but different structures.

    Epimers

    Carbohydrate isomers differing at only one carbon atom.

    Enantiomers

    Isomers that are mirror images of each other.

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    D-sugars

    The majority of sugars in humans, characterized as D isomers.

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    Importance of Carbohydrates

    Carbohydrates provide energy, structural components, and are abundant in nature.

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    Monosaccharides

    Simple sugars with the general formula (CH2O)n; contain either aldehyde or ketone groups.

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    Classification by Carbon Atoms

    Monosaccharides are classified by carbon count: trioses, tetroses, pentoses, hexoses, heptoses.

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    Disaccharides

    Carbohydrates formed by the combination of two monosaccharides, such as sucrose and lactose.

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    Polysaccharides

    Long chains of monosaccharide units, including starch and cellulose.

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    Oligosaccharides

    Short chains of 3-10 monosaccharide units, such as raffinose.

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    Structural Roles of Carbohydrates

    Carbohydrates serve structural roles in organisms, like chitin in insects and cellulose in plants.

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    Aldoses vs. Ketoses

    Monosaccharides can be classified into aldoses (with aldehyde groups) and ketoses (with ketone groups).

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    Glycosidic Bond

    A bond formed between the anomeric carbon of one sugar and an OH group of another sugar.

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    Reducing Sugar

    A sugar that has a free aldehyde or ketone group and can reduce other compounds.

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    Non-reducing Sugar

    A sugar that lacks a free aldehyde or ketone group, thus cannot act as a reducing agent.

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    Maltose

    A disaccharide made of two glucose molecules linked by an α(1→4) bond.

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    Lactose

    A disaccharide composed of galactose and glucose linked by a β(1→4) bond.

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    Sucrose

    A disaccharide formed from glucose and fructose linked by an α(1→2) bond.

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    Amylopectin bonds

    Main chain linked by α(1→4) bonds and side chains by α(1→6) bonds.

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    Maltose production

    Starch is converted to maltose by amylase.

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    Cellulose hydrolysis

    Yields D-glucose but humans cannot digest it.

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    Role of cellulase

    Enzyme that hydrolyzes cellulose; produced by certain microorganisms.

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    Chitin structure

    Polymer of N-acetyl-D-glucosamine with β-1→4 linkages.

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    N- and O-glycosides

    N-glycosides have –NH2, O-glycosides have –OH.

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    Hetero-polysaccharides

    Yield different sugars upon hydrolysis including glucuronic acid.

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    Complex carbohydrates

    Can attach to non-carbohydrate structures via glycosidic bonds.

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    Hemiacetal

    A product formed from the reaction of an alcohol with an aldehyde.

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    Hemiketal

    A product formed from the reaction of an alcohol with a ketone.

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    D-glucose forms

    D-glucose exists as an open-chain form and two cyclic forms: α and β-D-glucopyranose.

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    Cyclization in sugars

    Sugars can cyclize by forming a ring; glucose forms a six-membered ring, fructose forms a five-membered ring.

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    Haworth projection

    A representation of cyclic sugars where groups are shown in a ring structure.

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    Anomeric carbon

    The most oxidized carbon in a sugar molecule, connected to two oxygen atoms.

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    α-D-glucopyranose

    The cyclic form of D-glucose where the hydroxyl group on C1 is below the ring plane.

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    β-D-glucopyranose

    The cyclic form of D-glucose where the hydroxyl group on C1 is above the ring plane.

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    Fructose cyclization

    Fructose typically forms a five-membered ring known as a furanose during cyclization.

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    Chondroitin Sulphates

    Repetitive units of N-acetylgalactosamine and glucuronic acid; major GAGs in the body.

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    Heparin

    Anticoagulant composed of sulphated glucosamine and glucuronic acid; found in various organs.

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    Glycoproteins

    Proteins with covalently attached oligosaccharides; vary in carbohydrate content.

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    Functions of Membrane-bound Glycoproteins

    Involved in cell recognition, antigenicity, and protection.

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    Extracellular Matrix Components

    Glycoproteins compile the extracellular matrix and serve various protective roles.

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    Study Notes

    Carbohydrates: Structure and Function

    • Carbohydrates are the most abundant organic molecules in nature, serving various functions, including providing energy and forming cell membrane components.
    • They also play a crucial role as structural components in many organisms, such as bacterial cell walls (peptidoglycan), insect exoskeletons (chitin), and plant cell walls (cellulose).

    Classification of Carbohydrates

    • Monosaccharides: Classified by the number of carbon atoms (trioses, tetroses, pentoses, hexoses, heptoses).
      • Further categorized as aldoses (aldehyde group) or ketoses (ketone group) based on the functional group.
    • Disaccharides: Formed by the linkage of two monosaccharides via a glycosidic bond (e.g., sucrose, maltose, lactose).
    • Oligosaccharides: Consist of 3-10 monosaccharide units. Raffinose is an example.
    • Polysaccharides: Long chains of monosaccharides, serving diverse functions.
      • Storage polysaccharides (e.g., starch, glycogen): store glucose for later use.
      • Structural polysaccharides (e.g., cellulose, chitin): provide structural support.

    Isomers of Carbohydrates

    • Isomers are compounds with the same chemical formula but different structures.
    • Carbohydrate isomers can be epimers (differ in configuration around only one specific carbon atom) or enantiomers (mirror images).
      • Examples: glucose and mannose, glucose and galactose.
    • D-sugars are the most common type found in living organisms.

    Cyclization of Monosaccharides

    • Monosaccharides exist in linear and cyclic forms.
    • Ring closure often involves the -OH group on carbon 5 reacting with the carbonyl group (C=O), creating a hemiacetal or hemiketal.
    • Cyclic forms are designated as alpha (α) or beta (β) anomers depending on the position of the hydroxyl group on the anomeric carbon (carbon 1).

    Glycosidic Bonds

    • Glycosidic bonds are formed between the anomeric carbon of one monosaccharide and a hydroxyl group of another.
    • Alpha (α) or beta (β) linkages, depending on the orientation of the hydroxyl group.
    • Different glycosidic linkages lead to different structures and properties of the resulting disaccharides or polysaccharides.

    Reducing and Non-reducing Sugars

    • Reducing sugars have a free aldehyde or ketone group, allowing them to be oxidized.
    • Sucrose is a non-reducing sugar because both anomeric carbons are involved in the glycosidic bond, preventing oxidation.

    Polysaccharides: Homopolysaccharides and Heteropolysaccharides

    • Homopolysaccharides contain only one type of monosaccharide (e.g., starch, glycogen, cellulose, chitin).
    • Heteropolysaccharides contain more than one type of monosaccharide (e.g., glycosaminoglycans like hyaluronic acid and chondroitin sulfate).

    Glycoproteins and Proteoglycans

    • Glycoproteins are proteins with covalently attached oligosaccharides. Function in various cellular processes, including cell surface recognition and signaling.
    • Proteoglycans are a specialized type of glycoprotein characterized by the high concentration of carbohydrate.

    Carbohydrate Classification Summary

    • Monosaccharides (single sugars)
    • Disaccharides (two monosaccharides linked)
    • Oligosaccharides (3–10 monosaccharides linked)
    • Polysaccharides (many monosaccharides linked)
    • Homopolysaccharides (all the same sugar)
    • Heteropolysaccharides (more than one type of sugar)

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    Carbohydrates PDF

    Description

    Test your understanding of the cyclic structures of sugars, particularly glucose and fructose. This quiz covers key concepts such as hemiacetal formation and the differences between various sugar forms. Challenge yourself with questions about anomeric carbons, epimers, and isomers in monosaccharides.

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