Monosaccharides: Ketoses and Epimers

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Questions and Answers

What indicates that glucose is a reducing sugar?

It has an acyclic structure exclusively.

It cannot form a hexokinase product.

It can form cyclic structures only.

Copper is reduced from +2 to +1. (correct)

What is the role of glucose oxidase in glucose testing methods?

To measure the amount of NADP+ produced.

To oxidize D-Glucose to D-Glucono-δ-lactone. (correct)

To convert glucose into glucose-6-phosphate.

To catalyze the reduction of H2O2.

Which method uses NADP+ to indicate glucose levels?

Dextrostix Method

Fehling's Reaction

Clinistix Test

Hexokinase Method (correct)

What condition must be met for a monosaccharide to display reducing properties?

The sugar must be in acyclic form. Signup and view all the answers

In the testing strip methods, what does the oxidation of dianisidine indicate?

Color change proportional to glucose amount. Signup and view all the answers

What defines epimers among monosaccharides?

They differ only in the configuration of one chiral carbon atom. Signup and view all the answers

How many stereoisomers can be formed from a monosaccharide with four chiral carbons?

16 stereoisomers Signup and view all the answers

Which type of monosaccharide is D-fructose categorized as?

Ketohexose Signup and view all the answers

What is created at the new chiral center formed after cyclization of monosaccharides?

An anomer Signup and view all the answers

Which monosaccharide is an enantiomer of D-galactose?

L-galactose Signup and view all the answers

What structural feature characterizes a hemiacetal?

A carbon atom bonded to an aldehyde and an alcohol. Signup and view all the answers

Which statement is true regarding the cyclic structure of monosaccharides?

They can form stable cyclic structures from open-chain forms. Signup and view all the answers

Which of the following is NOT a characteristic of monosaccharides?

They contain only one type of functional group. Signup and view all the answers

What is the term for the interconversion of anomers via the acyclic form?

Mutarotation Signup and view all the answers

Which of the following statements about alpha and beta anomers of glucose is correct?

Beta anomer is favored at equilibrium due to its stability. Signup and view all the answers

What configuration differences exist between alpha and beta forms of D-glucopyranose?

They are epimers at the C1 carbon. Signup and view all the answers

What is the optical rotation of the equilibrium mixture of D-glucopyranose anomers?

+52.70 Signup and view all the answers

Why is the beta anomer of glucose more stable than the alpha anomer?

It has less steric hindrance due to equatorial positioning of hydroxyl groups. Signup and view all the answers

What type of stereoisomers are the alpha and beta anomers of glucose considered to be?

Diastereomers Signup and view all the answers

In the context of glucose structure, what are axial and equatorial positions significant for?

Reducing or increasing steric strain. Signup and view all the answers

Which ratio represents the stability difference between the anomers of D-glucopyranose?

36.4% for alpha and 63.5% for beta Signup and view all the answers

What type of affinity do selectins exhibit in cell recognition processes?

Low affinity Signup and view all the answers

Which lectins play a significant role in blood coagulation and inflammation?

Integrins Signup and view all the answers

What is the primary function of Eptifibatide (Integrilin®)?

Prevent platelet aggregation Signup and view all the answers

Which bacterium is known to adhere to the gastric surface through lectin recognition?

Helicobacter pylori Signup and view all the answers

What role do integrins play at the cellular level?

Serve as receptors conveying information Signup and view all the answers

Which of the following drugs is used in combination with Eptifibatide to enhance its effectiveness?

Aspirin Signup and view all the answers

Glycoconjugated blood group antigens interact with which type of protein in Helicobacter pylori?

Lectins Signup and view all the answers

What major health issue is associated with Helicobacter pylori infection?

Stomach cancer Signup and view all the answers

What is the primary function of the glycosidic bond in disaccharides?

To connect monosaccharides. Signup and view all the answers

Which of the following statements about lactose is true?

It contains one free anomeric hydroxyl group. Signup and view all the answers

What is a significant characteristic of cyclodextrins?

They form toroidal structures. Signup and view all the answers

Which type of bond primarily links glucose units in amylopectin?

α1→4 and α1→6 glycosidic bonds. Signup and view all the answers

What role does cellulose play in the biological context?

Structural component in plant cell walls. Signup and view all the answers

Which of the following accurately describes peptidoglycan?

It provides structural support to bacterial cell walls. Signup and view all the answers

What effect do penicillins have on bacterial cells?

They disrupt polysaccharide chain cross-linking. Signup and view all the answers

Which statement is true about glycoconjugates?

They can be formed by the conjugation of saccharides with steroids. Signup and view all the answers

What feature of heparin is notable for its biological function?

It has the highest negative charge density among biological macromolecules. Signup and view all the answers

The primary role of lectins in biological systems is to:

Bind carbohydrates with high affinity. Signup and view all the answers

What is the structural difference between gram-positive and gram-negative bacterial peptidoglycan?

Gram-negative has direct links without pentaglycine. Signup and view all the answers

What triggers immune responses during bacterial infections related to lipopolysaccharides?

Their recognition by vertebrate immune systems. Signup and view all the answers

Which of the following is a characteristic of glucosaminoglycans?

They are composed of repeating disaccharide units. Signup and view all the answers

Study Notes

Monosaccharide Series: Ketoses

Ketoses are a type of monosaccharide with a ketone functional group
Chiral centers are marked in red
Ketohexoses have 3, 4, and 5 asymmetric carbons resulting in 2^3 = 8 stereoisomers

Monosaccharide Series: Epimers

Epimers are two sugars that differ only in the configuration of one chiral carbon atom
Aldohexoses have 2, 3, 4, and 5 asymmetric carbons resulting in 2^4 = 16 stereoisomers
D-glucose is an epimer pf D-galactose
L-galactose is an enantiomer of D-galactose

Monosaccharides: Cyclic Structure

Monosaccharides exhibit special properties due to the presence of alcohol and carbonyl functionalities
High reactivity is a result of these functionalities
A new chiral center is created after cyclization
Anomers are stereoisomers that differ in stereochemistry at the hemiacetalic carbon
Alpha and Beta anomers are possible

Monosaccharides: Mutarotation

α-D-glucopyranose and β-D-glucopyranose are anomers of glucose
They interconvert via the open-chain form
This interconversion is called mutarotation
At equilibrium, the optical rotation of glucose is +52.7⁰
β-D-glucopyranose is more stable than α-D-glucopyranose because all its groups are equatorial
α and β anomers are diastereomers, only interconvertible by bond cleavage

Reducing Properties of Monosaccharides

Glucose is a reducing sugar because it can be oxidized
The reducing properties are due to the free anomeric hydroxyl group
The Fehling's reaction tests for reducing sugars

Glucose Measurement in Diagnosis and Treatment of Diabetes

Blood and urine glucose levels are monitored using enzymatic methods
Glucose oxidase method uses glucose oxidase and peroxidase to produce a colored product
Hexokinase method uses hexokinase and glucose-6-phosphate dehydrogenase to indirectly measure the amount of glucose

Disaccharides

Disaccharides contain a glycosidic bond formed by dehydration
Lactose is a disaccharide found in milk
Sucrose is a non-reducing disaccharide, the main circulating sugar in plants
Trehalose is a non-reducing disaccharide found in insects

Oligosaccharides

Cyclodextrins are cyclic oligomers of D-glucose linked α1→4
They are non-toxic and used in pharmaceutical formulations for drug delivery

Polysaccharides

Starch is a fuel-storage homopolysaccharide composed of amylose and amylopectin
Amylose is a linear polymer of D-glucose linked α1→4
Amylopectin is a branched polymer of D-glucose linked α1→4 and α1→6
Cellulose is a structural homopolysaccharide composed of D-glucose linked β1→4
Chitin is a structural homopolysaccharide composed of N-acetylglucosamine linked β1→4

Peptidoglycans

Peptidoglycans give bacterial envelopes strength and rigidity
They are composed of N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG) linked β1→4
Gram-positive bacteria have a thicker peptidoglycan layer than Gram-negative bacteria
Penicillins inhibit the formation of peptidoglycans by interfering with transpeptidases

Glucosaminoglycans

Linear heteropolysaccharides composed of repeating disaccharide units
Examples: Hyaluronic acid, chondroitin sulfate, keratan sulfate
Heparin is a highly sulfated glucosaminoglycan used as an anticoagulant

Glycoconjugates

Saccharides conjugated with steroids such as digoxin, a cardiac glycoside used in heart conditions
Lipopolysaccharides are found on the surface of Gram-negative bacteria and trigger immune responses

Lectin/Oligosaccharide Recognition

Lectins are proteins that bind carbohydrates with high affinity and specificity
Selectins are lectins involved in cell recognition and adhesion
Integrins are lectins that function as receptors, important in inflammation and blood coagulation

Diseases, Drugs, Diagnostics

Diseases affected by carbohydrates: diabetes, bacterial infections, heart conditions, thrombosis, viral infections, ulcers, stomach cancer
Drugs affecting carbohydrates: penicillins, digoxin, heparin, eptifibatide
Diagnostic methods for carbohydrate metabolism: Clinitab tablets, glucose oxidase and hexokinase methods

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Description

Explore the fascinating world of monosaccharides, focusing on ketoses and epimers. This quiz covers the structural variations, stereoisomerism, and cyclical formations of these crucial biomolecules. Test your knowledge of ketone functional groups and the properties that define monosaccharides.