Comprehensive Carbohydrate Chemistry and Water Metabolism Study Notes

Main Components of Living Organisms and Water Metabolism

• Main Components of Living Organisms:

  • Water
  • Carbohydrates and their derivatives
  • Proteins and amino acids
  • Lipids and their derivatives
  • Inorganic constituents:
    • Macrominerals (eight principal minerals): calcium, phosphorus, magnesium, sodium, potassium, sulfur, iron, and chlorine.
    • Trace elements (microminerals): copper, zinc, cobalt, selenium, manganese, and iodine.

• Water Content and Fluid Compartments:

  • Water constitutes approximately $70\%$ of total adult body weight.
  • Total body water volume is approximately $45\,L$.
  • Fluid Compartment Breakdown:
    • Intracellular Fluid (ICF): Inside cells, comprising $30\,L$.
    • Extracellular Fluid (ECF): Outside cells, comprising $15\,L$ total.
      • Tissue fluid (interstitial fluid): $12\,L$
      • Plasma: $3\,L$

• Physiological Functions of Water:

  • Functions as an excellent solvent inside the human body.
  • Regulates body temperature.
  • Serves as the vital medium for various metabolic pathways.
  • Facilitates the excretion of metabolic waste products in soluble form.
  • Aids in the digestion of foods via hydrolytic processes.
  • More essential to immediate survival than solid food; loss of approximately $20\%$ of total body water results in death.

• Water Balance:

  • Water Gain Sources:
    • Direct intake of water and other liquid fluids.
    • Water contained within ingested foods.
    • Metabolic water produced endogenously during metabolic processes: approximately $500\,mL/day$.
  • Water Loss Routes:
    • Urine: approximately $1\,L/day$.
    • Faeces (stool): approximately $100\,mL/day$.
    • Sweat and expired air (insensible loss): $600-1000\,mL/day$.
  • Imbalances:
    • Overhydration and Oedema: Occurs when water gain exceeds water loss.
    • Dehydration: Occurs when water loss exceeds water gain.

General Overview of Carbohydrates

• Definition and Composition:

  • Polyhydroxy aldehydes or polyhydroxy ketones, or substances that yield these compounds upon hydrolysis.
  • Composed elementally of carbon, hydrogen, and oxygen.
  • Nutritional sources include grains, vegetables, fruits, milk, and dairy products.

• Biomedical Importance:

  • Primary energy source for the body, yielding $4\,kcal/g$; stored as glycogen in animal tissues.
  • Serves critical structural roles, such as glycosaminoglycans in human tissues and cellulose in plant structures.
  • Essential constituent of nucleic acids (e.g., ribose in RNA and deoxyribose in DNA).
  • Facilitates cell-to-cell communication, recognition, and immune system function.
  • Non-digestible carbohydrates function as dietary fibers with important physiological roles.
  • Constitutes a basic food group essential for maintaining healthy metabolic function.

Structural and Nutritional Classification

• Structural Classification (Based on Number of Sugar Units):

  • Monosaccharides: Contain $1$ monomeric sugar unit.
  • Disaccharides: Contain $2$ monomeric sugar units.
  • Oligosaccharides: Contain $3-10$ monomeric sugar units.
  • Polysaccharides: Contain greater than $10$ monomeric sugar units.

• Nutritional Classification:

  • Simple Carbohydrates:
    • Induce a rapid rise in blood sugar levels.
    • Includes monosaccharides, disaccharides, and oligosaccharides.
  • Complex Carbohydrates (Polysaccharides):
    • Digested and converted slowly into monosaccharides.
    • Found in lentils, beans, peanuts, potatoes, corn, and whole grains.
    • Subdivided into starches (amylose, amylopectin), glycogen, and structural fibers (cellulose).

Monosaccharides

• Definition and General Features:

  • Sugars that cannot be further hydrolyzed into simpler carbohydrate units.
  • Serve as the fundamental building blocks of all higher carbohydrates.

• Classification by Number of Carbon Atoms:

  • Trioses: $3$ carbon atoms
  • Tetroses: $4$ carbon atoms
  • Pentoses: $5$ carbon atoms
  • Hexoses: $6$ carbon atoms
  • Heptoses: $7$ carbon atoms
  • Nanoses: $9$ carbon atoms

• Classification by Functional Group:

  • Aldoses: Contain an aldehyde functional group ($\text{C}=\text{O}$ at carbon 1).
  • Ketoses: Contain a keto functional group ($\text{C}=\text{O}$ at carbon 2).

• Combined Classification Matrix:

  • Triose ($3\text{C}$): Aldose = Glyceraldehyde | Ketose = Dihydroxyacetone
  • Tetrose ($4\text{C}$): Aldose = Erythrose | Ketose = Erythrulose
  • Pentose ($5\text{C}$): Aldose = Ribose, Xylose (epimer of ribose), Arabinose | Ketose = Ribulose, Xylulose (epimer of ribulose)
  • Hexose ($6\text{C}$): Aldose = Glucose, Galactose, Mannose | Ketose = Fructose
  • Heptose ($7\text{C}$): Ketose = Sedoheptulose

• Biochemical Importance of Key Hexoses:

  • Glucose (Aldohexose):
    • Known as grape sugar; serves as the main circulating blood sugar.
    • Normal fasting blood glucose level: 70-100\,mg/dL$.\n * Can be converted into all other carbohydrates required by the human body.\n * The principal sugar utilized by body tissues.\n * The exclusive metabolic fuel for mature red blood cells (RBCs).\n * The primary metabolic fuel for the brain and contracting skeletal muscle.\n * Fructose (Ketohexose):\n * Found abundantly in fruits and honey; exhibits significantly greater sweetness than glucose.\n * Metabolized predominantly in the liver.\n * Serves as the sugar of fetal blood and the principal energy-yielding sugar present in semen.\n * Galactose (Aldohexose):\n * Structural component of lactose (milk sugar); converted to glucose in the liver.\n * Combines with lipids or proteins in tissues to form galactolipids and glycoproteins.\n\n# Ring Structures and Stereoisomerism\n\n* **Ring Structure and Cyclization:**\n * Monosaccharides in solution exist predominantly in cyclic ring forms.\n * Intramolecular cyclization generates a new asymmetric carbon center known as the **anomeric carbon** (C_1$in aldoses,$C_2 in ketoses).\n * Glucose forms a stable six-membered ring known as glucopyranose (\alpha\text{-D-glucopyranose}$accounts for$36\%$,$\beta\text{-D-glucopyranose}$accounts for$63\% at equilibrium).\n * Fructose forms a stable five-membered ring structure (furanose).\n\n* **Asymmetric Carbon Atoms and Optical Isomerism:**\n * An asymmetric carbon atom (chiral center) is attached to four different atoms or chemical groups.\n * Formula for calculating total optical stereoisomers: 2^n$, where$n represents the number of asymmetric carbon atoms.\n * Ketoses possess one fewer asymmetric carbon atom than aldoses with the corresponding number of total carbons (n - 1).\n * Dihydroxyacetone is the only monosaccharide lacking asymmetric carbon atoms (n=0) and thus lacks optical activity.\n * Stereoisomer Count by Carbon Number:\n * 3\text{C}$Aldose ($n=1$):$2^1 = 2$isomers |$3\text{C}$Ketose ($n=0$):$2^0 = 0 isomers\n * 4\text{C}$Aldose ($n=2$):$2^2 = 4$isomers |$4\text{C}$Ketose ($n=1$):$2^1 = 2 isomers\n * 5\text{C}$Aldose ($n=3$):$2^3 = 8$isomers |$5\text{C}$Ketose ($n=2$):$2^2 = 4 isomers\n * 6\text{C}$Aldose ($n=4$):$2^4 = 16$isomers |$6\text{C}$Ketose ($n=3$):$2^3 = 8 isomers\n\n* **Optical Activity:**\n * The capacity to rotate the plane of polarized light either clockwise to the right (dextrorotatory, designated as +$or$d$) or counterclockwise to the left (levorotatory, designated as$-$or$l) due to chiral centers.\n * Racemic Mixture (dl$,$\pm): An equimolar mixture of two enantiomers that exhibits no net optical activity because the opposing rotations cancel each other out.\n\n* **Mutarotation:**\n * The spontaneous change in the specific optical rotation of an optically active sugar solution over time due to interconversion between \alpha$and$\beta anomers.\n * Freshly dissolved \alpha\text{-D-glucose}$exhibits a specific rotation of$+112^\circ.\n * Freshly dissolved \beta\text{-D-glucose}$exhibits a specific rotation of$+18.7^\circ$(or$+19^\circ).\n * Over several hours, both forms reach an equilibrium mixture exhibiting a stable specific rotation of +52.5^\circ$(or$+52.7^\circ).\n * Equilibrium composition: approximately 36\%$$\alpha\text{-anomer}$,$64\%$$\beta\text{-anomer}$, and a trace amount ($< 1\%) of open-chain aldehyde form.\n\n* **Types of Isomerism:**\n * Structural (Constitutional) Isomers: Isomers differing in functional groups, such as Ketose-Aldose isomerism (e.g., Glucose vs. Fructose, both sharing formula \text{C}6\text{H}{12}\text{O}6).\n * Stereoisomers (Spatial Isomers): Compounds with identical functional groups that differ in spatial configuration:\n * Enantiomers (\text{D}$and$\text{L} Isomerism): Non-superimposable mirror images differing at all asymmetric carbons. Sugar assignment depends on the spatial configuration around the reference asymmetric carbon furthest from the carbonyl group:\n * \text{D-Isomer}$:$\text{-OH} group on the right side (majority of physiological human sugars).\n * \text{L-Isomer}$:$\text{-OH} group on the left side.\n * Diastereomers: Non-mirror image stereoisomers.\n * Epimers: Stereoisomers differing in configuration around only a single asymmetric carbon atom (epimeric carbon), excluding the carbonyl carbon.\n * C_2\text{-Epimer} of Glucose = Mannose\n * C_4\text{-Epimer} of Glucose = Galactose\n * Anomers: Isomers differing specifically in \text{-OH}$orientation around the anomeric carbon atom generated upon ring closure ($C_1$in aldoses,$C_2 in ketoses):\n * \alpha\text{-Anomer}$:$\text{-OH} group positioned on the right/lower side relative to the ring plane.\n * \beta\text{-Anomer}$:$\text{-OH} group positioned on the left/upper side relative to the ring plane.\n\n# Physical and Chemical Properties of Monosaccharides\n\n* **Physical Properties:**\n * All monosaccharides are soluble in water.\n * All monosaccharides possess chiral centers (except dihydroxyacetone) and display optical activity and mutarotation.\n\n* **Chemical Properties:**\n * Reactions with Concentrated Acids:\n * Reaction with concentrated \text{H}_2\text{SO}_4 forms furfural or hydroxymethylfurfural derivatives, serving as the basis for Molisch's test (general test for all carbohydrates).\n * Alcoholic Fermentation:\n * Microorganisms (yeast and specific bacteria) obtain ATP energy anaerobically by fermenting sugars into ethanol and carbon dioxide:\n            \text{Sugar} \rightarrow \text{Ethanol} + \text{CO}_2 + \text{ATP}\n * Reactions of Hydroxyl (\text{-OH}) Groups:\n * Esterification: Reaction with acids to form sugar esters; phosphorylation with phosphoric acid to form glucose 6-phosphate represents the most biochemically significant ester.\n * Oxidation of Primary Alcohol Group (C_6): Selective oxidation of the terminal primary alcohol group yields uronic acids (e.g., Glucose yields Glucuronic acid; Galactose yields Galacturonic acid).\n * Glycoside Formation: Condensation between the anomeric \text{-OH}$group of a monosaccharide and an$\text{-OH} group of another compound (monosaccharide or non-carbohydrate aglycone). Forms glucosides (from glucose) or galactosides (from galactose).\n * Reactions of Carbonyl Group (\text{C}=\text{O}):\n * Reduction: Reduction of aldehyde or keto groups yields polyhydric sugar alcohols:\n * \text{D-Glucose} \rightarrow \text{D-Sorbitol}\n * \text{D-Mannose} \rightarrow \text{D-Mannitol}\n * \text{D-Fructose} \rightarrow \text{D-Sorbitol} + \text{D-Mannitol}\n * \text{D-Galactose} \rightarrow \text{D-Dulcitol (Galactitol)}\n * *Clinical Correlation:* Tissue accumulation of sorbitol and dulcitol promotes osmotic cellular swelling, contributing to diabetic cataracts and nephropathy.\n * Reducing Properties: Free carbonyl groups oxidize sugar into sugar acids while reducing cupric reagents (Fehling's and Benedict's tests), forming the clinical basis for detecting urinary glucose in diabetic patients.\n * Oxidation of Aldehyde Group (C_1):\n * Mild Oxidation: Yields Aldonic acids (e.g., Gluconic acid).\n * Strong Oxidation: Yields Aldaric acids (e.g., Glucaric acid).\n\n# Derived Sugars\n\n* **Definition:** Monosaccharide structural modifications that cannot be represented by the basic general sugar formula.\n\n* **Major Categories:**\n * Acid Sugars: Generated by oxidation (Uronic acids, Aldonic acids, Aldaric acids).\n * Sugar Alcohols: Generated by carbonyl reduction (Sorbitol, Galactitol, Mannitol).\n * Deoxy Sugars: Sugar units with an oxygen atom removed (e.g., Deoxyribose in DNA).\n * Amino Sugars: Sugar units where an \text{-OH} group is replaced by an amino group (e.g., Glucosamine, Galactosamine).\n * Glycosides: Condensation products of sugar anomeric centers with secondary alcohols or sugar groups.\n\n# Disaccharides\n\n* **General Formula:** \text{C}_n(\text{H}_2\text{O}){n-1}.\n* **Definition:** Glycosides formed by the condensation of two monosaccharide units with the elimination of one water molecule (\text{H}_2\text{O}). They are water-soluble and sweet.\n\n* **Classification:**\n * Reducing Disaccharides (retain a free carbonyl group with reducing capacity):\n * Maltose\n * Lactose\n * Isomaltose\n * Non-Reducing Disaccharides (lack a free carbonyl group):\n * Sucrose\n\n* **Detailed Disaccharide Profiles:**\n * Sucrose (Cane Sugar, Beet Sugar, Table Sugar):\n * Synthesized by plants.\n * Composition: \alpha\text{-D-glucose} + \beta\text{-D-fructose}.\n * Linkage: \alpha\text{-1,2} glucosidic linkage.\n * Properties: Lacks free aldehyde or keto groups; non-reducing (negative Benedict's/Fehling's tests); does not undergo mutarotation.\n * Hydrolysis: Hydrolyzed by dilute acids or sucrase (invertase) enzyme into D-glucose ([\alpha]_D = +52.5^\circ$) and D-fructose ($[\alpha]_D = -92^\circ).\n * *Invert Sugar:* Pure sucrose is dextrorotatory ([\alpha]_D = +66.5^\circ), but its hydrolyzed product mixture is overall levorotatory due to the strong levorotatory action of fructose. Thus, the product is termed invert sugar. Honey is largely invert sugar, explaining its intense sweetness.\n * Lactose (Milk Sugar):\n * Composition: \beta\text{-D-galactose} + \alpha\text{-D-glucose}.\n * Linkage: \beta\text{-1,4} galactosidic linkage.\n * Properties: Contains a free aldehyde group on glucose; reducing sugar; non-fermentable by yeast due to the absence of lactase in yeast cells.\n * *Biological Suitability for Infants:*\n * Resists yeast fermentation, preventing intestinal gas production and abdominal distention.\n * Moderately sweet, avoiding nausea and supporting adequate intake.\n * Provides the exclusive natural dietary source of galactose required for galactolipid synthesis in brain and nervous tissue.\n * Exerts a mild physiological laxative effect.\n * Maltose:\n * Composition: Two \alpha\text{-D-glucose} units.\n * Linkage: \alpha\text{-1,4} glucosidic linkage.\n * Source: Produced during starch digestion by salivary and pancreatic amylase.\n * Properties: Hydrolyzed by maltase to yield two glucose molecules; contains a free carbonyl group, exhibiting mutarotation and reducing properties.\n * Isomaltose:\n * Composition: Two glucose units.\n * Linkage: \alpha\text{-1,6} glucosidic linkage.\n * Source: Enzymatic cleavage product formed at branch points during starch and glycogen digestion by amylase.\n\n* **Clinical Correlation: Lactose Intolerance:**\n * Definition: A digestive disorder caused by deficiency or complete absence of the lactase enzyme in mucosal cells of the small intestine, impairing lactose cleavage.\n * Pathophysiology: Unabsorbed lactose remains in the intestinal lumen, drawing fluid via osmotic gradient into the gut. Upon reaching the large intestine, gut bacteria ferment unabsorbed lactose into short-chain organic acids and gases.\n * Clinical Symptoms (following dairy ingestion):\n * Abdominal distension and cramping\n * Watery osmotic diarrhea\n * Nausea\n * Flatulence and abdominal pain\n\n# Oligosaccharides and Glycoproteins\n\n* **Oligosaccharides:**\n * Condensation polymers yielding 3-10 monosaccharide units upon hydrolysis.\n * Usually exist conjugated to proteins (Glycoproteins, Proteoglycans) or lipids (Glycolipids).\n\n* **Glycoproteins:**\n * Proteins covalently bound to short, branched oligosaccharide chains (2-15$sugar units; carbohydrate content comprises less than$4\%$or$5\% of total molecular mass).\n * Biological Functions:\n * Structural components of the extracellular matrix (ECM).\n * Mucin secretions in the gastrointestinal tract (GIT).\n * Plasma proteins (comprises virtually all plasma proteins except albumin).\n * Integral cell membrane structural components and functional cell-surface receptors.\n * Secreted biological molecules including antibodies, hormones, and enzymes.\n * Circulating transport molecules (e.g., transferrin).\n\n# Polysaccharides\n\n* **General Properties:**\n * Complex macromolecular polymers composed of ten or more monosaccharides or derivative units held by glycosidic linkages.\n * High molecular weight compounds; sparingly soluble in water; non-sweet; non-reducing.\n\n* **Classification:**\n * Homopolysaccharides: Composed of a single repeating type of monosaccharide unit.\n * Heteropolysaccharides: Composed of differing repeating sugar units.\n\n* **Homopolysaccharides:**\n * Starch:\n * Storage form of carbohydrate in plants; main dietary sugar (\sim 60\% of human food intake).\n * Branched polymer of \alpha\text{-D-glucose}.\n * Constituents:\n * Amylose (13-20\%$): Inner layer, water-soluble, unbranched continuous polymer linked by$\alpha\text{-1,4} glycosidic bonds.\n * Amylopectin (80-87\%$): Outer layer, insoluble, branched polymer. Linear segments feature$\alpha\text{-1,4}$linkages; branches occur every$24-30$glucose units via$\alpha\text{-1,6} linkages. Contains a single reducing end.\n * Hydrolysis and Iodine Test Reactions:\n * Acid Hydrolysis: Complete heating with dilute acid yields glucose.\n * Enzymatic Hydrolysis: Cleavage by salivary/pancreatic amylases yields dextrins and maltose.\n * Iodine Chromatic Sequence:\n * Starch + Iodine \rightarrow Blue color\n * Soluble Starch + Iodine \rightarrow Blue color\n * Amylodextrin + Iodine \rightarrow Purple color\n * Erythrodextrin + Iodine \rightarrow Red color\n * Achroodextrin + Iodine \rightarrow Colorless\n * Maltose + Iodine \rightarrow Colorless\n * Glycogen (Animal Starch):\n * Storage homopolysaccharide in animal tissues composed of highly branched \alpha\text{-D-glucose} units.\n * Structure: Linear branches linked via \alpha\text{-1,4}$bonds; branch points linked via$\alpha\text{-1,6}$bonds every$12-14 glucose units.\n * Tissue Comparison:\n * Liver Glycogen: Comprises 8-10\%$of wet liver weight during postprandial states; depleted after$12-18 hours of fasting. Regulated by insulin (stimulates) and glucagon/adrenaline (inhibits). Functions to maintain normal blood glucose homeostasis during fasting.\n * Muscle Glycogen: Comprises 2\% of wet muscle weight; unaffected by brief fasting. Regulated by insulin (stimulates) and adrenaline (inhibits); lacks glucagon receptors. Serves as an immediate energy supply for muscle contraction; depletion directly causes exercise fatigue (basis for athletic carbohydrate loading).\n * Dextran:\n * Branched glucose homopolysaccharide.\n * Used clinically as a Plasma Volume Expander due to high viscosity and slow metabolic clearance, sustaining intravascular colloid osmotic pressure.\n * Inulin (Fructosan):\n * Soluble polymer composed exclusively of fructose units.\n * Not metabolized or hydrolyzed by human metabolic enzymes.\n * Administered clinically to evaluate renal clearance and measure Glomerular Filtration Rate (GFR).\n * Cellulose:\n * Unbranched linear polymer composed of \beta\text{-D-glucose}$units connected by$\beta\text{-1,4} glucosidic bonds.\n * Primary structural component of plant cell walls; insoluble in water.\n * Indigestible by humans due to lack of endogenous enzymes capable of cleaving \beta\text{-1,4} bonds.\n * Functions as major dietary fiber, increasing stool bulk, stimulating peristalsis, softening stool, and preventing constipation.\n\n# Glycosaminoglycans and Proteoglycans\n\n* **Heteropolysaccharides:**\n * Polymers yielding non-identical sugar constituents upon cleavage (e.g., pectins, gums, glycosaminoglycans).\n\n* **Glycosaminoglycans (GAGs / Mucopolysaccharides):**\n * Unbranched structural heteropolysaccharides consisting of repeating disaccharide units: `[Acidic Sugar - Amino Sugar]_n`.\n * Acidic Sugar Components: \text{D-Glucuronic acid}$or$\text{L-Iduronic acid} (epimer of glucuronic acid).\n * Amino Sugar Components: Glucosamine or Galactosamine.\n * *Exception:* Keratan sulfate lacks uronic acid (contains galactose instead).\n * Physical Characteristics: Highly polar molecules carrying dense negative charges; repel each other and bind water to generate viscous lubricating gel matrices. Not oxidized for cellular energy.\n * All GAGs covalently conjugate with core proteins to form proteoglycans, except hyaluronic acid (exists unattached in free form).\n * Physiological Functions:\n * Structural backbone of extracellular matrix (ECM).\n * Shock absorption and joint lubrication: Negative charge repulsion combined with high water retention provides resilience to mechanical compression.\n * Functions as structural tissue molecular sieves.\n * Anticoagulation (heparin).\n\n* **Key GAG Members:**\n * Mucoitin Sulphate: Present in respiratory and gastrointestinal tract mucous secretions.\n * Chondroitin Sulphate: Most abundant human GAG; located in cartilage, bone, tendons, aorta, and cornea.\n * Hyaluronic Acid: Unsulfated GAG not bound to core protein; present in synovial fluid, vitreous body of eye, cartilage, and loose connective tissue. Functions as joint lubricant and mechanical cushion.\n * Heparin: Intracellular anticoagulant GAG.\n * Heparan Sulphate: Located on cell surfaces and basement membranes. Acts as cell surface receptor mediating cell growth, adhesion, and signaling; provides charge-selectivity for renal glomerular filtration in kidney basement membranes.\n * Keratan Sulphate: Essential for maintaining corneal transparency in conjunction with dermatan sulphate.\n * Dermatan Sulphate: Principal GAG of skin, cornea, sclera, and blood vessel walls.\n\n* **Comparative Analysis: Proteoglycans vs. Glycoproteins:**\n * Proteoglycans:\n * Carbohydrate content: > 95\%\n * Structure: Long, linear, unbranched disaccharide repeat chains (> 50 units) attached to a central core protein ("bottle-brush" geometry). Forms massive proteoglycan aggregates with hyaluronic acid via link proteins.\n * Function: Ground substance and load-bearing support in bone, cartilage, and ECM.\n * Glycoproteins:\n * Carbohydrate content: < 5\%$(or$< 4\%\n * Structure: Short, highly branched oligosaccharide chains (2-15 units) lacking repeating disaccharide motifs attached to protein.\n * Function: Cell membrane receptors, enzymes, antibodies, plasma proteins, mucin, select hormones.\n\n# Dietary Fibers\n\n* **Definition:** Complex dietary carbohydrates indigestible by human digestive enzymes.\n\n* **Classification:**\n * Soluble Fibers: Pectins and Gums. Found in oats, oat bran, fruits, vegetables, lentils, apples, avocados, strawberries, barley, and beans.\n * Insoluble Fibers: Cellulose, Hemicellulose, and Lignin. Found in whole-grain products, wheat bran, lentils, sweet potatoes, and whole-wheat bread.\n\n* **Nutritional and Physiological Importance:**\n * Prevents constipation by softening stool and enhancing gut motility.\n * Slows gastric emptying rate, promoting prolonged stomach fullness and satiety.\n * Binds large volumes of lumenal water and sequesters potential toxic compounds.\n * Reduces the statistical incidence of gastrointestinal cancers.\n * Improves systemic glucose tolerance by blunting the rate of intestinal glucose absorption.\n * Lowers plasma cholesterol levels by impairing dietary cholesterol absorption and binding bile salts to enhance fecal excretion.\n\n# Questions and Discussion\n\n* **Short Answer Explanations:**\n * *Question:* Explain why lactose is considered the perfect sugar for infants.\n * *Answer:* Lactose is non-fermentable by yeast (prevents gas and distention), moderately sweet (prevents nausea), provides galactose essential for infant neural galactolipid synthesis, and exerts a mild physiological laxative effect.\n * *Question:* Explain why sucrose is classified as a non-reducing sugar.\n * *Answer:* Sucrose forms via an \alpha\text{-1,2}$glycosidic bond engaging the anomeric aldehyde carbon of glucose ($C_1$) and the anomeric keto carbon of fructose ($C_2). Lacking any free anomeric aldehyde or keto group, it cannot reduce copper reagents.\n * *Question:* Name two examples of reducing disaccharides.\n * *Answer:* Maltose, Lactose (or Isomaltose).\n\n* **Multiple Choice Questions:**\n * *Question:* A disaccharide linked by \alpha\text{-1,4} glucosidic linkage is:\n * a. Lactose | b. Sucrose | c. Cellulose | d. Maltose\n * *Answer:* d. Maltose\n * *Question:* A disaccharide linked by \beta\text{-(1,4)} galactosidic linkage is:\n * a. Lactose | b. Sucrose | c. Cellulose | d. Maltose\n * *Answer:* a. Lactose\n * *Question:* A mucopolysaccharide that does not contain Uronic acid is:\n * a. Heparan Sulfate | b. Heparin | c. Chondroitin Sulfate | d. Keratan Sulfate\n * *Answer:* d. Keratan Sulfate\n * *Question:* Which of the following is a heteropolysaccharide?\n * a) Chondroitin sulfate | b) Starch | c) Glycogen | d) Dextran\n * *Answer:* a) Chondroitin sulfate\n * *Question:* The reducing ability of a carbohydrate is due to the presence of:\n * a) A free carboxyl group | b) A free hydroxyl group | c) Presence of an \alpha\text{-1,4} linkage | d) A free carbonyl group\n * *Answer:* d) A free carbonyl group\n * *Question:* Which one of the following is considered a derived sugar?\n * a) Glucose | b) Galactose | c) Gluconic acid | d) Lactose\n * *Answer:* c) Gluconic acid\n * *Question:* Glucose and galactose are epimers and differ structurally in the orientation of \text{H}$and$\text{OH} on:\n * a) C_1$| b)$C_3$| c)$C_2$| d)$C_4\n * *Answer:* d) C_4\n * *Question:* Which of the following pairs are enantiomers?\n * a. D-Galactose and L-Glucose | b. d-Galactose and l-Glucose | c. d-Mannose and l-Mannose | d. D-glucose and L-Glucose\n * *Answer:* d. D-glucose and L-Glucose\n * *Question:* Which of the following is a homopolysaccharide?\n * a) Chondroitin sulfate | b) Hyaluronic acid | c) Dextrin | d) Mucoitin sulphate\n * *Answer:* c) Dextrin\n * *Question:* Which of the following is NOT a polymer of glucose?\n * a) Amylose | b) Inulin | c) Cellulose | d) Glycogen\n * *Answer:* b) Inulin\n * *Question:* Starch and glycogen are polymers of:\n * a. Fructose | b. Mannose | c. \beta\text{-D-Glucose}$| d.$\alpha\text{-D-Glucose}\n * *Answer:* d. \alpha\text{-D-Glucose}$$
  • Question: Which of the following is NOT hydrolyzed by amylase?
    • a) Starch | b) Glycogen | c) Cellulose | d) Dextrin
    • Answer: c) Cellulose
  • Question: Which of the following glycosaminoglycans is unsulfated?
    • a) Chondroitin sulfate | b) Heparin | c) Hyaluronic acid | d) Keratan sulfate
    • Answer: c) Hyaluronic acid
  • Question: Invert sugar is defined as:
    • a. Lactose | b. Sucrose | c. Mannose | d. Hydrolytic products of sucrose
    • Answer: d. Hydrolytic products of sucrose