Carbohydrate Classification and Structures
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Questions and Answers

Which carbohydrate cannot be digested by humans due to the absence of specific enzymes?

  • Maltose
  • Glucose
  • Cellulose (correct)
  • Starch

    • What is the approximate ratio of carbon, hydrogen, and oxygen in carbohydrates?

  • 1 : 3 : 1
  • 1 : 1 : 1
  • 1 : 2 : 1 (correct)
  • 2 : 1 : 2

    • Which carbohydrate classification does not require hydrolysis?

  • Oligosaccharide
  • Disaccharide
  • Monosaccharide (correct)
  • Polysaccharide

    • Which of the following statements about α-D-Glucose is correct?

    <p>It can be broken down by the enzyme α-amylase.</p> Signup and view all the answers

    Which of the following statements about the hydration of carbohydrates is incorrect?

    <p>All carbohydrates can be directly converted to their polysaccharide forms without enzymes.</p> Signup and view all the answers

    What structural form do carbohydrates typically adopt according to Fischer projections?

    <p>Both linear and cyclic forms</p> Signup and view all the answers

    Which of the following statements about chirality in carbohydrates is true?

    <p>Glyceraldehyde has one chirality center.</p> Signup and view all the answers

    Which carbohydrate structure is responsible for the main storage form of energy in animals?

    <p>Glycogen</p> Signup and view all the answers

    What is the primary characteristic of monosaccharides?

    <p>They cannot be further reduced by hydrolysis.</p> Signup and view all the answers

    Which monosaccharide is primarily known as blood sugar?

    <p>Glucose</p> Signup and view all the answers

    What condition arises from the absence of an enzyme required to convert galactose to glucose?

    <p>Galactosemia</p> Signup and view all the answers

    Which of the following statements about fructose is true?

    <p>It is sweeter than glucose.</p> Signup and view all the answers

    What is the significance of insulin in the context of glucose metabolism?

    <p>It regulates blood glucose levels by promoting glucose uptake.</p> Signup and view all the answers

    Galactose is primarily found in which of the following?

    <p>Milk products</p> Signup and view all the answers

    What is the primary consequence of galactose accumulation in the blood and tissues?

    <p>Mental retardation and cataract formation</p> Signup and view all the answers

    Which statement correctly describes the relationship between glucose and carbohydrates?

    <p>Glucose can be stored as polysaccharides like starch.</p> Signup and view all the answers

    What signifies a D isomer in sugar structures?

    <p>The hydroxyl group on the reference carbon is positioned to the right.</p> Signup and view all the answers

    What is the result of aldehydes and ketones reacting with alcohol?

    <p>They form hemiacetals or hemiketals in a 1:1 ratio.</p> Signup and view all the answers

    Which structural feature is present in a cyclic hemiacetal?

    <p>It has a hydroxyl group and an alkoxy group on the same carbon.</p> Signup and view all the answers

    Which statement about cyclic structures of sugars is correct?

    <p>They contain an additional asymmetric carbon atom.</p> Signup and view all the answers

    How can α and β forms of cyclic hemiacetals be distinguished?

    <p>By the spatial arrangement of the hydroxyl groups.</p> Signup and view all the answers

    What characteristic defines a chiral carbon?

    <p>It is bonded to exactly four different substituents.</p> Signup and view all the answers

    What happens when cyclic hemiacetals form?

    <p>They create a stable cyclic structure with added chirality.</p> Signup and view all the answers

    What best describes the stability of a cyclic hemiacetal compared to its linear form?

    <p>Cyclic hemiacetals are generally more stable than linear forms.</p> Signup and view all the answers

    What type of bond connects the two glucose molecules in maltose?

    <p>α-1,4-glycosidic bond</p> Signup and view all the answers

    Which disaccharide is formed from glucose and galactose?

    <p>Lactose</p> Signup and view all the answers

    Which of the following statements is true about sucrose?

    <p>It has an α,β-1,2-glycosidic bond.</p> Signup and view all the answers

    What characterizes the glycosidic bond in lactose?

    <p>It is a β-1,4-glycosidic bond.</p> Signup and view all the answers

    Which artificial sweetener is hydrolyzed into phenylalanine?

    <p>Aspartame</p> Signup and view all the answers

    What distinguishes sucrose from maltose and lactose in terms of its chemical structure?

    <p>It comprises a glucose and a fructose.</p> Signup and view all the answers

    Which of the following is NOT true regarding maltose?

    <p>It contains a β-1,4-glycosidic bond.</p> Signup and view all the answers

    Which artificial sweetener was linked to cancer concerns in the 1970s?

    <p>Saccharin</p> Signup and view all the answers

    What is the structural characteristic of cellulose that distinguishes it from starch?

    <p>It is composed of unbranched chains with β-1,4-glycosidic bonds.</p> Signup and view all the answers

    What enzyme is necessary for the digestion of maltose into glucose units?

    <p>α-maltase</p> Signup and view all the answers

    Which of the following statements accurately describes glycosaminoglycans (GAGs)?

    <p>They consist of alternating amino sugar and glucuronate units.</p> Signup and view all the answers

    What is the main dietary role of cellulose in human nutrition?

    <p>Functions as an insoluble fiber adding bulk to waste.</p> Signup and view all the answers

    Which amino sugar is abundantly found in nature and is known for maintaining joint cartilage health?

    <p>D-glucosamine</p> Signup and view all the answers

    What is the function of heparin in the body?

    <p>Helps prevent blood clotting.</p> Signup and view all the answers

    Which blood type does not have antigens on the red blood cells?

    <p>Type O</p> Signup and view all the answers

    What is the primary structural bond in chitin that differentiates it from other polysaccharides?

    <p>β-1,4-glycosidic bond</p> Signup and view all the answers

    Study Notes

    Carbohydrate Classification

    • Carbohydrates are the most abundant organic compounds in nature, comprising nearly half of the earth’s biomass.
    • They make up 3/4 of the weight of plants but only 1% of the weight of animals and humans.
    • Carbohydrates are classified according to their number of sugar units:
      • Monosaccharides: consist of one sugar molecule.
      • Disaccharides: consist of two monosaccharide units linked by a glycosidic bond.
      • Polysaccharides: consist of many monosaccharide units linked by glycosidic bonds.

    Alpha vs. Beta Carbohydrates

    • Carbohydrates can exist in two forms: alpha (α) and beta (β).
    • α-glucose is found in starch products such as pasta, while β-glucose is found in cellulose such as wood or paper.
    • Humans can digest starch but not cellulose because they have the enzyme α-amylase but not β-amylase.

    Chirality

    • All carbohydrates have one or more chirality centers, meaning they can exist as mirror images (enantiomers).
    • The simplest aldose, glyceraldehyde, has one chirality center and two enantiomers.
    • Fischer projections are used to represent the three-dimensional structure of carbohydrates in two dimensions.

    D-Isomer

    • Most hexoses in living organisms are D-isomers.
    • In a Fischer projection, a hexose is a D-isomer if the hydroxyl group on the reference carbon is on the right.

    Cyclic Structure - Haworth Structure

    • Cyclic hemiacetals form readily when the hydroxyl and carbonyl groups are part of the same molecule.
    • Cyclic hemiacetals/hemiketals contain an additional asymmetric carbon atom and can exist in two stereoisomeric forms designated as α and β.

    Monosaccharides

    • Monosaccharides are simple sugars that cannot be further reduced by hydrolysis.
    • They are directly absorbed into the bloodstream from the small intestine.
    • Glucose is the most abundant monosaccharide and is found in fruits, vegetables, corn syrup, and honey.
    • Fructose is the sweetest carbohydrate and is found in fruit juices and honey.
    • Galactose is a monosaccharide that combines with glucose to form lactose (milk sugar).

    Disaccharides

    • Disaccharides are composed of two monosaccharide units linked by a glycosidic bond.
    • Maltose is a disaccharide of two glucose molecules linked by an α-1,4-glycosidic bond.
    • Lactose is disaccharide of glucose and galactose linked by a β-1,4-glycosidic bond.
    • Sucrose is a disaccharide of glucose and fructose linked by an α,β-1,2-glycosidic bond and is the most common sugar found in table sugar.

    Glycosidic Bonds

    • A glycosidic bond is a covalent bond formed by a condensation reaction between the hemiacetal group of one saccharide and the hydroxyl group of another saccharide.

    Polysaccharides

    • Polysaccharides are complex carbohydrates made up of many monosaccharide units linked by glycosidic bonds.
    • Starch is a polysaccharide of glucose units found in amylose and amylopectin.
    • Cellulose is a polysaccharide of glucose units linked by β-1,4-glycosidic bonds and is the main structural material in plants. Humans cannot digest cellulose.
    • Glycogen is a highly branched polysaccharide of glucose units that serves as the storage form of glucose in animals.

    Useful Carbohydrates

    • Amino sugars contain an -NH2 group in place of an -OH group.
      • Glucosamine is the most abundant amino sugar in nature and is used for maintaining healthy cartilage in joints.
      • Chitin is another abundant amino sugar and is a component of the exoskeletons of insects and crustaceans.
    • Glycosaminoglycans (GAGs) are unbranched carbohydrates composed of alternating amino sugar and glucuronate units.
      • Hyaluronate is found in extracellular fluids and helps lubricate joints.
      • Chondroitin is a component of cartilage and tendons.
      • Heparin prevents blood clotting and is stored in the mast cells of the liver.

    Blood Types

    - Blood type is determined by specific carbohydrates attached to red blood cells.
- There are four main blood types: A, B, AB, and O.

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    Carbohydrates Types, Structure, Composition and Uses PDF

    Description

    This quiz covers the classification of carbohydrates, including monosaccharides, disaccharides, and polysaccharides. It also explores the differences between alpha and beta carbohydrates, and the concept of chirality in carbohydrates. Test your understanding of these essential organic compounds and their properties.

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