Monosaccharides and Glucose Hemiacetals Quiz

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Questions and Answers

What percentage of alpha D glucose is present at equilibrium after mutarotation?

64%

16%

36% (correct)

50%

Which test is considered a confirmatory test for identifying monosaccharides?

Barfoed’s test

Osazone test (correct)

Benedict’s test

Fehling's test

What is the initial specific rotation of the plane polarized light when passed into a fresh solution of alpha D glucose?

+0°

+52.5°

+112° (correct)

+19°

Which reagent is NOT part of the Benedict’s test for detecting reducing substances?

Hydrochloric acid Signup and view all the answers

What color change indicates the presence of glucose in urine when performing Benedict’s test?

Green to brick red Signup and view all the answers

What is the resultant structure formed when glucose reacts with itself to create an intramolecular hemiacetal?

A six-membered ring structure known as a pyranose Signup and view all the answers

Which term describes the isomeric forms of monosaccharides that differ in configuration about the anomeric carbon?

Anomers Signup and view all the answers

What describes the leftward rotation of polarized light by a sugar solution?

Levorotatory light rotation Signup and view all the answers

Which carbon atom becomes asymmetric when glucose forms an intramolecular hemiacetal?

C-1 Signup and view all the answers

What are hemiacetals and hemiketals derived from?

Reactions between alcohols and aldehydes or ketones Signup and view all the answers

What color indicates a severe concentration of sugar in Benedict's test?

Brick red precipitate Signup and view all the answers

Which disaccharide is produced during the digestion of starch by pancreatic alpha amylase?

Maltose Signup and view all the answers

What is the bond type between the units in sucrose?

α (1→2) glycosidic bond Signup and view all the answers

Which clinical condition results from a defect in the enzyme lactase?

Lactose intolerance Signup and view all the answers

Which of the following is true about trehalose?

It has an α (1→1) glycosidic bond. Signup and view all the answers

What is the result of lactose accumulating in the gut due to lactose intolerance?

Diarrhea Signup and view all the answers

Which disaccharide is commonly known as malt sugar?

Maltose Signup and view all the answers

What distinguishes sucrose from other disaccharides?

It contains both anomeric carbons in the glycosidic bond. Signup and view all the answers

Which of the following statements accurately describes carbohydrates?

They serve as the main energy source for all organisms. Signup and view all the answers

What is the significance of glucose in biological systems?

It provides energy and is involved in the production of amino acids and fatty acids. Signup and view all the answers

Which of the following is true about D sugars?

Only D sugars can be metabolized by the body. Signup and view all the answers

What are the products of hydrolysis of carbohydrates?

Monosaccharides or compounds producing them. Signup and view all the answers

In which type of carbohydrate classification would lactose fall?

Disaccharide Signup and view all the answers

Which carbohydrate is recognized as an intermediate of the HMP shunt?

Erythrose Signup and view all the answers

What is a key structural role of carbohydrates in organisms?

They are components of cell membranes. Signup and view all the answers

What characterizes the empirical formula of carbohydrates?

They are hydrates of carbon represented as (C.H2O)n. Signup and view all the answers

Which polysaccharide serves as the major storage form of energy in animals?

Glycogen Signup and view all the answers

What is the optical activity of dextrorotatory sugars?

They turn the plane of polarized light to the right. Signup and view all the answers

What are the two main components of starch?

Amylose and Amylopectin Signup and view all the answers

Which statement accurately describes the structure of glycogen?

Every 11th sugar molecule has a branch. Signup and view all the answers

What is the primary dietary role of cellulose in humans?

It aids in digestion by preventing constipation. Signup and view all the answers

What type of glycosidic bond connects the glucose units in amylose?

Alpha 1, 4 linkages Signup and view all the answers

During digestion, starch is broken down to form what primarily?

Dextrins Signup and view all the answers

What is the primary interaction of starch with iodine solution during a laboratory test?

It forms a blue colored complex. Signup and view all the answers

Which of the following statements about inulin is correct?

It contains beta 1, 4 linkages. Signup and view all the answers

Which carbohydrate serves as the stored nutrient in plant tissues?

Starch Signup and view all the answers

What is the primary function of inulin in clinical tests?

It acts as a marker for glomerular filtration rate. Signup and view all the answers

Which sugar units are primarily joined by β-1,4 glycosidic linkages in chitin?

N-acetyl glucosamine units. Signup and view all the answers

What role does hyaluronic acid play in the human body?

It acts as a structural support and lubricant. Signup and view all the answers

Which statement about heparin is accurate?

Heparin inhibits blood coagulation by binding to antithrombin. Signup and view all the answers

Which property is true regarding mucopolysaccharides or glycosaminoglycans (GAGs)?

They play a role in structural support and lubrication. Signup and view all the answers

Hyaluronidase, an enzyme released by some pathogens, has what effect on hyaluronic acid?

It hydrolyzes glycosidic linkages, making tissues more susceptible to infections. Signup and view all the answers

Which of the following is NOT a function of chondroitin sulfate?

Serves as an anticoagulant. Signup and view all the answers

What type of linkage connects the units in heparin?

α-1,4 linkage. Signup and view all the answers

Study Notes

Carbohydrates: Structure and Classification

Carbohydrates are hydrates of carbon (H₂O of C).
They are the most abundant organic molecules in nature.
Their empirical formula is (CH₂O)ₙ.
They are classified as monosaccharides, disaccharides, and polysaccharides.

Definition

Carbohydrates are defined as polyhydroxyaldehydes or ketones, or compounds that produce them on hydrolysis.

Importance of Carbohydrates

They are the most abundant dietary source of energy (4 Cal/g) for organisms.
They are precursors for many organic compounds (e.g., fats, amino acids, ketone bodies).
Carbohydrates (e.g., glycoproteins and glycolipids) participate in cell structure, cell growth, adhesion, and fertilization.
They are structural components of many organisms (e.g., plant fiber (cellulose), insect exoskeletons, and microorganism cell walls).
They serve as the storage form of energy (e.g., glycogen) to meet immediate energy needs.

Structure of Carbohydrates

Examples include D-glyceraldehyde, D-glucose, and D-fructose.
Molecular structures are shown in the slides.

Classification of Carbohydrates

Classification is based on the number of carbon atoms.
Monosaccharides are further categorized into aldoses and ketoses, with examples of trioses, tetroses, pentoses, hexoses, and heptoses.
Disaccharides are formed from two monosaccharides linked by glycosidic bonds. Examples include maltose, sucrose, lactose, and trehalose.
Polysaccharides are long chains of monosaccharides. They are categorized into homopolysaccharides (e.g., starch, glycogen, cellulose, inulin, dextrans, chitin), and heteropolysaccharides (e.g., hyaluronic acid, heparin, chondroitin sulphate, dermatan sulphate, keratan sulphate).

Importance of Monosaccharides

Key monosaccharides include glyceraldehyde, erythrose, ribose, glucose, and galactose.
Glyceraldehyde and erythrose are intermediates in glycolysis and HMP shunt.
Ribose is an essential component of nucleic acids.
Glucose provides energy and produces amino acids and fatty acids.
Galactose is an essential component of milk, used to produce lactate.

Stereoisomers of Glyceraldehyde

D-glyceraldehyde and L-glyceraldehyde.

D and L Isomerism of Glucose

Naturally occurring sugars are D-sugars.
The body can metabolize only D-sugars.

Optical Activity

Dextrorotatory (d) (+) : sugar solution rotates plane-polarized light to the right.
Levorotatory (l) (-) : sugar solution rotates plane-polarized light to the left.

Different Representations of Glucose Structure

Open chain projection.
Fischer's formula.
Haworth formula.

Formation of Ring Structure

Ring structures form via hemiacetal reactions.
D-glucose exists as an intramolecular hemiacetal.

Anomers/Anomeric Carbon

Isomers that differ only in their configuration about the anomeric carbon are called anomers.
The anomeric carbon is the hemiacetal carbonyl carbon.
For aldoses (e.g., glucose), the 1st carbon is the anomeric carbon; for ketoses (e.g., fructose), the 2nd carbon is the anomeric carbon.

Glucose in Pyranose Form

α-D-glucose and α-D-glucopyranose.

α and β Forms of D-Glucose

α-D-glucose and β-D-glucose are shown in different representations.

Fructose in Furanose Form

α-D-fructose furanose.

α and β Anomers of D-Fructose

α-D-fructose and β-D-fructose are shown in furanose form.

Epimerism

Sugars differ only in the configuration around one carbon atom.
Examples include D-glucose and D-galactose (differ at the 4th carbon), and D-glucose and D-mannose (differ at the 2nd carbon).

Examples for Epimers

Structures of D-mannose, D-glucose, and D-galactose are shown.

Mutarotation

A change in the specific rotation of an optically active sugar in solution over time.

Mutarotation (Example)

A fresh solution of a-D-glucose rotates plane-polarized light at + 112° and changes to +52.5° after 12-18 hours.

Reactions of Monosaccharides

Oxidation, reduction, dehydration, formation of esters, and glycoside formation are discussed

Reducing Properties

Sugars with a free aldehyde or ketone group at the anomeric carbon are reducing sugars; their reduction can be tested via Benedict's test, Fehling's test, and Barfoed's test.
Osazone test is a confirmatory test for monosaccharides.
Reduction occurs more efficiently in alkaline than acidic solutions.

Benedict's Test: Principle

The principle of Benedict's test.

Benedict's Test

A simple method for identifying reducing substances (like glucose) in urine.

Benedict's Test Procedure

Add the Benedict's reagent followed by the urine sample, heat for a few seconds.
The color change from green to brick red indicates glucose presence, with color intensity correlating with glucose concentration.

Clinical Applications of Benedict's Test

Semi-quantitative test to determine sugar concentration in urine.
Color changes reflect glucose levels:
0% sugar – blue
Mild (0.5-1%) – green
Moderate (1-1.5%) – yellow
Severe (1.5-2%) – brick red precipitate
Used to diagnose diabetes mellitus.

Importance of Disaccharides

Maltose, lactose, sucrose, and trehalose are highlighted

Maltose

A malt sugar formed from two α-D-glucose units linked by an α(1→4) glycosidic bond.
Produced during starch digestion by pancreatic alpha-amylase.

Lactose

Found in milk.
Composed of β-D-galactose and α-D-glucose linked by a β(1→4) glycosidic bond.
Hydrolyzed by the enzyme lactase to glucose and galactose.
Lactose intolerance is due to insufficient lactase activity.

Sucrose

A cane sugar formed from an α-D-glucose and a β-D-fructose linked by an α(1→2) glycosidic bond.
Non-reducing sugar.

Trehalose

A disaccharide with two glucose units linked by an α(1→1) glycosidic bond.
Found in some plants, fungi, and insects.
Non-reducing sugar

Polysaccharide: Homopolysaccharides

Starch: Stored carbohydrate in plants (e.g., cereals, roots, tubers, vegetables).
Glycogen: Storage carbohydrate in animals (liver, muscle).
Cellulose: Plant structural component, dietary fiber.
Inulin: Found in onion, garlic, etc.
Dextrans: A polymer of glucose commonly found in microorganisms.
Chitin: Exoskeleton component in various insects and crustacean.

Starch

A carbohydrate reserve in plants; found in cereals, roots, tubers, and vegetables.
Consists of amylose (water-soluble) and amylopectin (water-insoluble) components.

Amylose

A linear, unbranched chain of glucose units linked by α(1-4) glycosidic bonds -

Amylopectin

A branched chain of glucose units, with α(1-6) linkages at the branch points.

Test for Starch

Iodine test: Starch reacts with iodine solution to form a blue-colored complex.

Starch Digestion in the Body

Starch is digested to dextrins by salivary alpha-amylase and further hydrolyzed into maltose by pancreatic alpha-amylase and glucose units.

Glycogen

Animal storage carbohydrate in liver and muscles.
More branched than amylopectin; every 11th glucose unit is branched .
Synthesized in the body through the process of glycogenesis..

Cellulose

Plant structural component; made of glucose units linked by β(1-4) glycosidic bonds. - Cannot be digested by humans due to lack of cellulase enzyme.

Inulin

Found in onion, garlic, etc.
Composed of fructose units linked by β(2-1) linkages
Clinical purpose: used to monitor kidney function.

Chitin

Structural component of exoskeletons of crustaceans (e.g., crabs, lobsters) and insects.
Composed of N-acetyl glucosamine units joined by β(1→4) glycosidic linkages.

Importance of Heteropolysaccharides (GAGs)

Hyaluronic acid: lubricant, shock absorber..
Heparin: anticoagulant.
Chondroitin sulfate: maintains tissue structure.
Dermatan sulfate: maintains tissue structure.
Keratan sulfate: important in corneal transparency.

Proteoglycans and Glycoproteins

Proteoglycans: Heavily glycosylated proteins, found in extracellular matrix (e.g., decorin).
Glycoproteins: Less glycosylated proteins, found on cell membranes or in body fluids (e.g., mucins).

Structure of a Proteoglycan

Glycoprotein

A typical membrane glycoprotein.

Clinical Aspects of Mucopolysaccharidoses

Inborn errors in metabolism; excess accumulation of GAGs in the body tissues.
Deficiency of lysosomal enzymes that degrade GAGs.

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Description

Test your knowledge on the properties and reactions of monosaccharides, specifically focusing on alpha D glucose. This quiz covers topics such as mutarotation, confirmatory tests, and structural transformations within sugars. Perfect for students studying biochemistry or organic chemistry.