Carbohydrates Introduction and Functions
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Questions and Answers

What is primarily broken down by the body to produce glucose for energy?

  • Fructose
  • Starch and glycogen (correct)
  • Cellulose
  • Sucrose

    • Which polysaccharide is commonly known as an energy storage molecule in animals?

  • Chitin
  • Glycogen (correct)
  • Cellulose
  • Starch

    • What role do carbohydrates play in the formation of other biological molecules?

  • They act only as energy sources.
  • They can only be used for immediate energy.
  • They serve exclusively as structural components.
  • They are metabolic precursors for amino acids and fats. (correct)

    • Regarding carbohydrates, which statement is correct?

    <p>Polysaccharides include starch, glycogen, and cellulose. (C)</p> Signup and view all the answers

    Which laboratory skill is among the learning objectives for understanding carbohydrates?

    <p>Isolation of glycogen from chicken liver (A)</p> Signup and view all the answers

    In which context do carbohydrates mainly act as an energy source?

    <p>In animal respiration (C)</p> Signup and view all the answers

    What type of molecule do plants convert light energy into for energy storage?

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

    Which of the following is NOT a carbohydrate?

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

    What does the reference plane for ring atoms generally involve?

    <p>It usually contains three or four ring atoms. (D)</p> Signup and view all the answers

    In the designation of ring conformation, how are atoms above and below the reference plane notated?

    <p>Atoms above as superscripts and below as subscripts. (B)</p> Signup and view all the answers

    How many atoms are in the planar configuration of ribose in its envelope form?

    <p>4 atoms (B)</p> Signup and view all the answers

    What are the major and minor forms of the twisted cyclic ribose conformation?

    <p>C3’-endo major and C2’-exo minor. (B)</p> Signup and view all the answers

    What representation suggests monosaccharides are flat, yet does not reflect their actual structure?

    <p>The Haworth representation. (B)</p> Signup and view all the answers

    Which configuration do pyranoses adopt to achieve low energy?

    <p>Chair configuration. (A)</p> Signup and view all the answers

    Which of the following forms is minor among the dominant forms of twisted cyclic ribose?

    <p>C2’-exo. (B)</p> Signup and view all the answers

    What is one reason for the non-planarity of furanose and pyranose rings?

    <p>The tetrahedral nature of carbon bonds. (C)</p> Signup and view all the answers

    What product is formed from the reduction of a monosaccharide?

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

    Which reducing agent is specifically mentioned as capable of reducing the carbonyl group of monosaccharides?

    <p>NaBH4 (B)</p> Signup and view all the answers

    What is a unique characteristic of alditols compared to their aldose precursors?

    <p>Alditols cannot cyclize (D)</p> Signup and view all the answers

    Which alditol is produced from the reduction of glucose using sodium borohydride?

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

    What technique is applied to determine glycosidic linkages in sugars?

    <p>Exhaustive methylation of all free hydroxyl groups (D)</p> Signup and view all the answers

    Which of the following monosaccharides can produce more than one alditol upon reduction?

    <p>D-fructose (C)</p> Signup and view all the answers

    What product is obtained from exhaustive methylation of trehalose followed by hydrolysis?

    <p>2,3,4,6-tetra-O-methyl-D-glucopyranose (D)</p> Signup and view all the answers

    Which of the following compounds is classified as a sugar alcohol?

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

    Which disaccharide is known as milk sugar and found in dairy products?

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

    What enzyme is responsible for the digestion of sucrose in the small intestine?

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

    Which of the following statements about glycosidic linkages is correct?

    <p>They can involve the anomeric carbon of one sugar and any -OH group of another sugar. (C)</p> Signup and view all the answers

    What is the most common dietary disaccharide?

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

    What are the primary functions of polysaccharides in nature?

    <p>Structural support, energy storage, and cellular communication (C)</p> Signup and view all the answers

    Which disaccharide is commonly found in beer and resulting from the fermentation of malt?

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

    Which monosaccharides combine to form maltose?

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

    Which type of glycosidic linkage is associated with high molecular weight polysaccharides?

    <p>Both α- and β-glycosidic linkages (C)</p> Signup and view all the answers

    What is the primary structural difference between glycogen and starch?

    <p>Glycogen is more extensively branched than starch. (D)</p> Signup and view all the answers

    What type of linkage connects glucose units in cellulose?

    <p>β(1→4) linkages (A)</p> Signup and view all the answers

    What characteristic of glycogen allows for rapid glucose release?

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

    How does the orientation of glucose units in cellulose contribute to its stability?

    <p>Each glucose unit is flipped 180° relative to others. (A)</p> Signup and view all the answers

    Which of the following best describes the physical form of glycogen within cells?

    <p>It appears as a globular granule. (B)</p> Signup and view all the answers

    What is the role of hydrogen bonds in the structure of cellulose?

    <p>To stabilize the linear chains (D)</p> Signup and view all the answers

    What is the approximate number of glucose units that may be contained in a single glycogen granule?

    <p>30,000 glucose units (D)</p> Signup and view all the answers

    Which polysaccharide serves as a major structural component of plant cell walls?

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

    Which glycosaminoglycan is known for its high viscosity and serves as a lubricant in synovial fluid?

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

    Which of the following glycosaminoglycans has the highest net negative charge and acts as a natural anticoagulant?

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

    What is a primary function of proteoglycans in the extracellular matrix?

    <p>Act as lubricants and shock absorbers (C)</p> Signup and view all the answers

    What type of linkage connects the disaccharide units in hyaluronic acid?

    <p>β(1⟶4) and β(1⟶3) glycosidic linkages (A)</p> Signup and view all the answers

    Which statement about dermatan sulfate is true?

    <p>It is a key component of the extracellular matrix of skin. (A)</p> Signup and view all the answers

    Which glycosaminoglycan is primarily found in tendons and cartilage?

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

    What is the molecular weight of glycosaminoglycans like hyaluronic acid commonly up to?

    <p>10 million daltons (C)</p> Signup and view all the answers

    Which function is NOT associated with proteoglycans?

    <p>Acting as solvents for fatty substances (C)</p> Signup and view all the answers

    Flashcards

    Carbohydrates definition

    Abundant biomolecules, one of three main nutrients (along with proteins and fats).

    Carbohydrates function (energy)

    Serve as a primary energy source. Plants convert light energy, Animals obtain energy from plant carbs.

    Polysaccharides types

    Large carbohydrate molecules like glycogen, starch, and cellulose.

    Starch and glycogen breakdown

    Broken down into glucose for immediate energy or stored in liver/muscles.

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    Glucose

    Simple sugar produced from starch and glycogen breakdown.

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    Metabolic Precursors

    Carbohydrates are the building blocks of other molecules like amino acids and fats

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    Learning Objective 1

    Understanding how the structure, properties, and reactivity of carbohydrates affect their functions in the body

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    Learning Objective 2-4

    Laboratory-based learning on glycogen isolation, carbohydrate testing, or glucose estimation in drinks.

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    Ribose Conformational Types

    Ribose, a sugar in nucleic acids, exists in two main puckered forms (cyclic): C3'-endo/C2'-exo and C2'-endo/C3'-exo.

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    Ribose (sugar-pucker) conformations

    Ribose's ring structure isn't flat; it adopts twisted shapes.

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    Haworth Projection

    A simplified representation of sugars, showing a flat ring structure though isn't planar in reality.

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    Pyranose Conformation

    Pyranose sugars, similar to cyclohexane, adopt low-energy chair or boat conformations

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    Reference Plane

    A plane used to specify the location of ring atoms above or below for sugar conformations.

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    Sugars: Not planar

    The ring structures of sugars (like ribose and pyranose) are not flat, but rather adopt 3-D conformations.

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    C3'-endo

    An important configuration of ribose, where carbon 3' is inside the ring (in the reference plane).

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    C2'-exo

    An important configuration of ribose, where carbon 2' is outside the ring.

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    Alditol

    A polyhydroxy compound formed by reducing the carbonyl group of a monosaccharide. It is a sugar alcohol.

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    Reduction of a Monosaccharide

    The process of converting the carbonyl group (C=O) of a monosaccharide to an hydroxyl group (OH) using reducing agents like NaBH4 or H2 with a metal catalyst.

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    C2 Racemization

    When reducing D-fructose, the carbon at position 2 can change its configuration, leading to a mixture of alditols.

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    Exhaustive Methylation

    The process of adding methyl groups (CH3-) to all free hydroxyl groups in a sugar molecule, often used to determine glycosidic linkages.

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    Glycosidic Linkages

    Covalent bonds between two monosaccharide units, formed by the reaction of the anomeric carbon of one sugar with a hydroxyl group of another sugar.

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    Trehalose

    A disaccharide composed of two glucose units linked by an α, α-1,1-glycosidic bond.

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    2,3,4,6-tetra-O-methyl-D-glucopyranose

    A fully methylated glucose molecule, meaning all four free hydroxyl groups are replaced by methyl groups.

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    Sorbitol

    A sugar alcohol formed by reducing glucose. It is used as a sweetener in sugar-free products.

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    Disaccharides

    Sugars composed of two monosaccharide units joined by a glycosidic bond.

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    Maltose

    A disaccharide formed by two glucose molecules linked by an α-1,4-glycosidic bond.

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    Polysaccharides

    Large polymers made up of many monosaccharide units linked by glycosidic bonds.

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    Cellulose

    A polysaccharide that serves as a structural component of plant cell walls.

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    Glycogen Structure

    Glycogen is a highly branched glucose polymer with α(1→4) linkages forming linear chains and α(1→6) linkages creating branches. This branching pattern allows for rapid glucose release, especially when glucose availability is limited.

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    Glycogen Granule

    Glycogen is stored in the cytoplasm of cells as spherical granules, which contain a core protein called glycogenin surrounded by branches of glucose units.

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    Cellulose Structure

    Cellulose, a structural component of plant cell walls, is a linear polymer of glucose units linked by β(1→4) glycosidic bonds. The glucose units are arranged in a straight chain, allowing for strong intermolecular hydrogen bonding.

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    Cellulose Bonding

    The β(1→4) glycosidic bonds in cellulose create a linear structure, allowing for extensive hydrogen bonding both within and between cellulose chains. This contributes to cellulose's strong and rigid structure.

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    Cellulose Conformation

    Each glucose unit in cellulose is flipped 180° relative to its neighbors, resulting in an almost fully extended molecule. This arrangement allows for optimal hydrogen bonding and contributes to its structural strength.

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    Glycogen vs. Starch

    Glycogen is similar to amylopectin (a component of starch) but is more extensively branched. This means glycogen has more α(1→6) linkages, making it more compact and allowing for faster glucose release.

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    Carbohydrate Function: Energy

    Carbohydrates are a primary source of energy for living organisms. They are broken down into glucose, which is used for immediate energy production or stored as glycogen or starch.

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    Carbohydrate Structure: Diversity

    Carbohydrates exhibit a wide range of structures, from simple sugars like glucose to complex polymers like glycogen and cellulose. These structural variations influence their functions in living organisms.

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    Glycosaminoglycans

    Long, unbranched polysaccharides made up of repeating disaccharide units. They are negatively charged due to the presence of sulfate and carboxyl groups.

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    Hyaluronic Acid

    A type of glycosaminoglycan found in connective tissues, synovial fluid, and the vitreous humour of the eye. It forms highly viscous solutions, providing lubrication and support.

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    Heparin

    A glycosaminoglycan with the highest net negative charge. It acts as a natural anticoagulant by binding to antithrombin III, inhibiting blood clotting.

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    Chondroitin and Keratan Sulfate

    Types of glycosaminoglycans found in connective tissues like tendons and cartilage, contributing to their strength and elasticity.

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    Dermatan Sulfate

    A glycosaminoglycan found in skin, contributing to its structure and flexibility.

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    Proteoglycans

    Large macromolecules that consist of one or more glycosaminoglycan chains covalently attached to a protein core.

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    Functions of Proteoglycans

    They serve as lubricants, provide tensile strength and elasticity to soft tissues, act as shock absorbers, create passageways in the extracellular matrix, and aid in removing cellular debris and pathogens.

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    Proteoglycans in the Extracellular Matrix

    Proteoglycans are often found embedded in the extracellular matrix, the space between cells, holding cells together and providing structural support.

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    Study Notes

    Carbohydrates Introduction

    • Carbohydrates are the most abundant bioorganic molecules on Earth.
    • They are one of three main nutrients, alongside proteins and fats.
    • Many carbohydrates are polysaccharides (e.g., glycogen, starch, cellulose).
    • Our bodies break down starch and glycogen into glucose for immediate energy or storage.
    • Carbohydrates are metabolic precursors to other molecules like amino acids and fats.

    Learning Objectives

    • Relate carbohydrate structure, properties, and reactivity to their functions.
    • Isolate glycogen from chicken liver.
    • Interpret results of carbohydrate qualitative tests.
    • Estimate glucose content in commercially available drinks.

    Functions of Carbohydrates

    • Energy storage: Plants convert light energy into monosaccharides and starch; animals use this for energy.
    • Structural components: Cellulose, chitin, and bacterial cell walls.
    • Nucleic acid components: Ribose and deoxyribose.
    • Cell-cell recognition: Carbohydrates on cell surfaces play key roles.
    • Biological membranes: Glycolipids are components.

    Structure, Nomenclature, and Classification

    • Carbohydrates are polyhydroxy aldehydes or ketones, or compounds that produce these upon hydrolysis.
    • Monosaccharides (simple sugars) have the general formula Cn(H2O)n.
    • Oligosaccharides are formed from a few monosaccharides.
    • Polysaccharides are formed from many monosaccharides.
    • Carbohydrates are classified by complexity:
      • Monosaccharides (e.g., glucose, fructose, mannose, galactose).
      • Disaccharides (e.g., sucrose, maltose, cellobiose).
      • Oligosaccharides.
      • Polysaccharides (e.g., starch, cellulose, glycogen).

    Monosaccharides

    • Cannot be hydrolyzed to simpler carbohydrates.
    • General formula Cn(H2O)n (where n is 3-8).
    • Can be aldoses (aldehyde group) or ketoses (ketone group).
    • Classified by the number of carbon atoms (e.g., triose, tetrose, pentose, hexose, heptose).
    • Hexoses are the most common.

    Common Monosaccharides

    • Glucose: Blood sugar, dextrose, grape sugar; the most abundant monosaccharide in our bodies. Provides energy (ATP) to cells.
    • Fructose: Levulose, sweetest monosaccharide; energy source; naturally found in honey, fruits, and vegetables.
    • Galactose: Energy source; component of glycolipids and glycoproteins; part of lactose (milk sugar).
    • Mannose: Converted to glucose in the body; found in certain bacteria, fungi, and plants; used in treating carbohydrate-deficient glycoprotein syndrome.

    Fischer Projection

    • A common method for representing open-chain carbohydrates.
    • The carbon chain is vertical; the lowest numbered carbon is at the top.
    • Numbering follows the convention that the most oxidized end of the molecule has the lowest number.

    Epimers

    • Differ in the arrangement about one chiral carbon.
    • Example: Glucose and mannose.

    Haworth Projection

    • A diagrammatic representation for the ring forms of sugars.
    • Represents the placement of substituents in relation to the plane of the paper, showing how glucose can exist in a cyclic form.
    • Important for understanding the stereochemistry of carbohydrates.

    Conformational Structures

    • Sugars exist in various conformations.
    • The terms describing conformations are: chair, boat, skew-boat
    • Haworth Diagrams are simplified representations reflecting the ring structures.

    Oxidation of Monosaccharides

    • Oxidation reactions with weak oxidizing agents (Benedict's, Barfoed's, Fehling's) convert monosaccharides into their corresponding acids (e.g., glucose to gluconic acid).
    • Oxidation can be used to identify or quantify specific carbohydrates.
    • Additional oxidation produces uronic acids from the hydroxymethyl groups.

    Reduction of Monosaccharides

    • Reduction of the carbonyl group of monosaccharides forms alditols (sugar alcohols).
    • Example: Glucose to glucitol (sorbitol)
    • Alditols cannot cyclize.

    Exhaustive Methylation

    • Methylation of all free hydroxyl groups allows identification of glycosidic linkages.
    • Can be utilized to determine glycosidic linkages and the component monosaccharides.
    • Example: Methylation of trehalose.

    Formation of Derivatives

    • Esterification: Phosphate groups transfer to carbohydrates, important for metabolism (e.g., glucose to glucose-6-phosphate).
    • Glycoside Formation: A hydroxyl group (of the anomeric carbon) in a carbohydrate is replaced by an OR group (from an alcohol or another carbohydrate), making it a glycoside.
    • Formation of amino sugars: Amino groups substitute for hydroxyl groups (e.g., glucose to glucosamine).
    • Formation of sugar sulfates: Sugar sulfates are found in proteoglycans (e.g., chondroitin sulfates).
    • Formation of N-acetylneuraminates: Often found as a terminal residue in oligosaccharides (e.g., sialic acid).
    • Important for recognition, protection, and biological roles.

    Disaccharides

    • Formed by joining two monosaccharides via a glycosidic bond.
    • Examples include maltose, lactose, and sucrose.
    • Only monosaccharides can be absorbed from the digestive tract.
    • Disaccharides are digested into their constituent monosaccharides for absorption into the bloodstream.

    Polysaccharides

    • Large, complex molecules composed of repeating monosaccharide units joined by glycosidic bonds.
    • Classification:
      • Homoglycans: contain only one type of monosaccharide (e.g., starch, glycogen).
      • Heteroglycans: contain more than one type of monosaccharide (e.g., glycosaminoglycans).

    Storage Polysaccharides: Starch

    • Major source of carbohydrate in the human diet (about 50% of carbohydrate intake).
    • Synthesized from glucose from photosynthesis in plants, stored in roots and seeds.
    • Consists of two types: amylose (linear) and amylopectin (branched).
    • Both consist of repeating glucose units in a-1,4 linkages; amylopectin has additional a-1,6 linkages.

    Storage Polysaccharides: Glycogen

    • Storage form of glucose in animals.
    • Found in liver and muscle cells.
    • Highly branched structure with more α(1→6) linkages, allowing for rapid glucose release.

    Other Homoglycans: Cellulose

    • Major structural component of plant cell walls.
    • Consists of long, linear chains of glucose linked by β-1,4 linkages.
    • Its structure enables intermolecular hydrogen bonding that makes it strong.
    • Humans lack the enzyme needed to break down ß-1,4 linkages.

    Other Homoglycans: Chitin

    • Structural component of exoskeletons of insects and crustaceans, cell walls of fungi.
    • Repeating units of N-acetyl-β-D-glucosamine connected by β-1,4 linkages.
    • Structural component of exoskeletons and cell walls in various organisms.

    Other Homoglycans: Alginic Acid and Dextran

    • Alginic acid: structural polysaccharide of brown algae.
    • Dextran: produced by lactic acid bacteria; used as a food additive or in chromatography.

    Other Homoglycans: Pectic Acid

    • Polygalacturonic acid
    • Intercellular layers of plant tissues and functions.

    Heteroglycans: Glycosaminoglycans

    • Long linear polysaccharides consisting of repeating disaccharide units that contain an amino sugar and often negatively charged sulfate or carboxyl groups.
    • Functions: lubricants, tensile strength, elastic properties to soft tissues, acts as shock absorber, and helps in disposing of unwanted cellular artifacts.
    • Major components of mucins, connective tissues, and extracellular matrix, such as hyaluronic acid, chondroitin sulfates, keratin sulfates, dermatan sulfates, and heparin.

    Other Heteroglycans

    • Glycosaminoglycans and glycosamino glucuronoglycans are examples of heteroglycans
    • These have a variety of functions.

    Peptidoglycans

    • Major components of bacterial cell walls.
    • Consists of repeating disaccharide units alternating with short peptides.
    • Crucial for bacterial structural integrity.
    • Site for bacterial identification (e.g. gram-positive/gram-negative).

    Lipopolysaccharides (LPS)

    • Found in the outer membrane of Gram-negative bacteria
    • Consist of lipid and carbohydrate components.
    • Play important roles in the antigenic properties of gram-negative bacteria.

    Glycoproteins

    • Proteins with covalently attached oligosaccharides.
    • Important for a variety of functions, from cell-surface recognition to protein function and structure.
    • O-linked oligosaccharides are attached to hydroxyl groups of serine or threonine, N-linked glycosaminoglycans are attached to hydroxyl groups of asparagine, and N-linked are linked to amide nitrogen.
    • Examples include blood group antigens and mucus production.

    O-linked and N-linked oligosaccharides

    • Types of glycosidic linkages between each oligosaccharide and protein.
    • Key determinants for antigenicity.
    • Important for cell recognition processes.

    Exercises

    • Questions, answers to test student understanding.

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    Carbohydrate Reading Module PDF

    Description

    Explore the fundamental roles and properties of carbohydrates in living organisms. This quiz covers carbohydrate structure, functions, and practical applications, including glycogen isolation and glucose estimation in beverages. Understand how carbohydrates impact energy storage and structural components in biology.

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