Carbohydrates Overview

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Questions and Answers

What are anomers in the context of monosaccharides?

Isomers differing in the position of a hydroxyl group

Stereoisomers that differ in the configuration around the anomeric carbon (correct)

Carbohydrates that can exist in both ring and linear forms

Carbohydrates with the same molecular formula but different structures

Which of the following is a role of glycoproteins as glycoconjugates?

Serving as structural components of cell membranes

Facilitating cell-cell recognition and signaling (correct)

Storage of carbohydrates for energy

Acting as enzymes to catalyze reactions

Which method is commonly used for monitoring glucose levels in patients?

Testing blood or urine glucose levels with specific diagnostic strips or devices (correct)

Use of penicillin to regulate blood sugar

Regular intake of polysaccharides to balance glucose levels

Dosing with digoxin to control insulin spikes

Which characteristic defines polysaccharides among the types of carbohydrates?

They typically have a high molecular weight and can have branched structures. Signup and view all the answers

What is the primary function of the drug heparin in medical treatments?

To inhibit clotting in thrombosis prevention Signup and view all the answers

Which type of carbohydrate consists of single units of polyhydroxyaldehyde or ketone?

Monosaccharides Signup and view all the answers

What is the primary role of carbohydrates in metabolism?

Energy generation and storage Signup and view all the answers

Which of the following is an example of a polysaccharide?

Cellulose Signup and view all the answers

What distinguishes aldoses from ketoses in monosaccharides?

Location of the carbonyl group Signup and view all the answers

Which of the following suffixes is commonly used for naming carbohydrates?

-ose Signup and view all the answers

How many monosaccharide units are typically found in oligosaccharides?

3-10 units Signup and view all the answers

Which configuration indicates that the hydroxyl group is on the right in Fischer projection?

D configuration Signup and view all the answers

What is the smallest monosaccharide?

Glyceraldehyde Signup and view all the answers

Which type of carbohydrate serves as a recognition element in immune response?

Polysaccharides Signup and view all the answers

What role do carbohydrates play as excipients in pharmaceuticals?

Inactive ingredients Signup and view all the answers

What is the primary condition for a sugar to exhibit reducing properties?

It must adopt an acyclic form Signup and view all the answers

Which chemical reaction demonstrates that glucose is a reducing sugar?

Fehling’s reaction Signup and view all the answers

What must be true for a sugar to be considered a reducing sugar based on its structure?

It has one free anomeric OH Signup and view all the answers

Which of the following sugars is NOT a reducing sugar?

Sucrose Signup and view all the answers

What role does D-Glucose oxidase play in glucose measurement?

It oxidizes glucose to produce hydrogen peroxide Signup and view all the answers

What is the primary consequence of lactose intolerance?

Inability to break down lactose Signup and view all the answers

Which method is commonly used for self-monitoring glucose levels?

Glucose Oxidase method Signup and view all the answers

What is the result of the reaction between H2O2 and dianisidine in the glucose oxidase method?

It produces a color change Signup and view all the answers

Which disaccharide is commonly known as milk sugar?

Lactose Signup and view all the answers

What is the significance of the free anomeric carbon in monosaccharides?

It enables the sugar to reduce other compounds Signup and view all the answers

What is the role of β-lactamases in bacterial resistance?

They express resistance by cleaving β-lactam antibiotics. Signup and view all the answers

How does clavulanic acid help in combating bacterial resistance?

It is a suicide inhibitor of β-lactamase. Signup and view all the answers

Which of the following is a characteristic of heparin?

It is used as an anticoagulant. Signup and view all the answers

What type of joints are affected by glucosaminoglycans?

Synovial joints. Signup and view all the answers

Which statement about lipopolysaccharides is correct?

They are recognized by vertebrate immune systems. Signup and view all the answers

What is a common use of Digoxin?

In the treatment of heart conditions. Signup and view all the answers

What is the average molecular weight (MW) of low molecular weight heparin (LMWH)?

4,500 Signup and view all the answers

What are lectins primarily known for?

Binding carbohydrates with high affinity and specificity. Signup and view all the answers

Which glucosaminoglycan is directly associated with cartilage?

Chondroitin sulfate. Signup and view all the answers

What is the average molecular weight of heparin?

15,000 Signup and view all the answers

What is the total number of stereoisomers possible for a sugar with 4 chiral carbons?

16 Signup and view all the answers

Which statement correctly distinguishes D and L configurations in monosaccharides?

L sugars have a hydroxyl group on the left of the chiral center. Signup and view all the answers

What is an anomer?

Stereoisomers differing at the hemiacetal carbon. Signup and view all the answers

What happens during the process of mutarotation?

Interconversion between two anomers via the acyclic form. Signup and view all the answers

Which of the following statements about epimers is correct?

Epimers only differ in configuration at one chiral carbon. Signup and view all the answers

Which sugar is an enantiomer of D-galactose?

L-galactose Signup and view all the answers

In the cyclic structure of pyranoses, which conformation is generally more stable?

Equatorial-equatorial conformers Signup and view all the answers

During the conversion of anomers, which form is involved?

Acyclic form Signup and view all the answers

What does it mean for two sugars to be diastereomers?

They have the same molecular formula but different configurations. Signup and view all the answers

Which sugar is an example of a ketohexose?

D-fructose Signup and view all the answers

What is the significance of the penultimate carbon in sugars?

It is the second to last carbon in the chain. Signup and view all the answers

What type of reaction creates a new chiral center in sugars after cyclization?

Nucleophilic cycloaddition Signup and view all the answers

Which of the following statements is true regarding the Haworth perspective formulas?

They illustrate the spatial orientation of cyclic sugars. Signup and view all the answers

Why is α-D-glucopyranose less stable than β-D-glucopyranose?

There are more dipolar repulsions in α. Signup and view all the answers

Study Notes

Carbohydrates

Polyhydroxyaldehydes or polyhydroxyketones with the general formula (CH2O)n, often containing N, S, or P.
Can be linear or cyclic.
Oligomers and polymers can form upon hydrolysis.
Also known as saccharides, named with the suffix “-ose”.
Classified into monosaccharides, oligosaccharides, and polysaccharides.

Monosaccharides

Single units of polyhydroxyaldehyde or ketone.
Examples include glucose, fructose, erythrose.

Oligosaccharides

Few units linked via ether bonds.
Example: Sucrose, a disaccharide containing one unit of D-glucose and one unit of D-fructose.

Polysaccharides

More than 20 monosaccharide units, some with over 100,000 units.
Can be linear or branched.
Examples: Amylose (linear), amylopectin, and glycogen (branched).

Carbohydrate Roles

Energy generation and storage: Oxidation of carbohydrates is the primary energy-generating process in metabolism.
Structural role: Found in plants (cellulose), bacterial cell walls, and insect exoskeletons.
Pharmaceutical formulations: Used as inactive ingredients (excipients) in tablets, capsules, and other formulations.
Osmolites: Contribute to osmotic pressure inside and outside cells.
Recognition elements: Play a role in immunity, immune response, cell identity, and recognition.

Monosaccharide Types and Nomenclature

Two main types: polyhydroxyaldehydes (aldoses) and polyhydroxyketones (ketoses).
Classified based on the number of carbon atoms: trioses, tetroses, pentoses, hexoses.

Monosaccharide Chirality

Glyceraldehyde, the smallest monosaccharide, has two stereoisomers.
Most natural sugars have the D relative configuration.

Fischer Projection

2D representation of 3D molecular structure showing the configuration of all chiral centers.
The longest C-chain is written vertically with the most highly oxidized C on top.
Horizontal lines represent bonds projecting forward, vertical lines represent bonds projecting to the rear.
C atoms at the intersection of horizontal and vertical lines are not shown and are numbered sequentially from the top.
The OH group on the most distant chiral carbon from the carbonyl group determines the relative configuration:
- Right: D configuration.
- Left: L configuration.

Monosaccharide Series: Aldoses

Most natural sugars have the D relative configuration.
Each chiral carbon generates two enantiomers.
The total number of stereoisomers for a sugar with n chiral carbons is 2n.
Only half of these will have the D-relative configuration.

Monosaccharide Series: Ketoses

Ketones with multiple hydroxyl groups.
Also classified based on the number of carbon atoms.

Monosaccharide Series: Epimers

Two sugars that differ only in the configuration of one chiral carbon atom.

Hexose

Six-carbon sugar.
Aldohexose (aldehydes with six carbons).
Ketohexose (ketones with six carbons).
Examples include D-glucose, D-galactose, L-galactose, and D-fructose.

Monosaccharides: Cyclic Structure

Monosaccharides exhibit special properties due to the presence of both alcohol and carbonyl functionalities.
Cyclic structures are formed through intramolecular nucleophilic cycloaddition, creating a new chiral center called the anomeric carbon.

Anomers

Stereoisomers that differ in the stereochemistry at the hemiacetalic carbon (in aldoses) or hemiketalic carbon (in ketoses) formed by the cyclization.
Cyclic forms of monosaccharides are in equilibrium with an open-chain form creating mutarotation.

The Anomers of Glucose and Fructose

Glucose forms pyranose rings (six-membered rings).
Fructose forms furanose rings (five-membered rings).

Monosaccharides: Mutarotation

Interconversion of α and β anomers via the open-chain form.
At equilibrium, a mixture of both α and β anomers exists.

Conformational Formulas of Pyranoses

The pyranose ring is not flat but 3D.
Two chair forms exist: equatorial-equatorial (no steric hindrance) and axial-axial (steric hindrance).
Equatorial conformations are less hindered and more stable.

Combined Effect of Conformation and Configuration

The stability of α and β anomers of D-glucopyranose is influenced by conformation and configuration.
α-D-glucopyranose has a 1,2 dipolar repulsion making it less stable compared to β-D-glucopyranose where all groups are equatorial, making it more stable.
α and β anomers are diastereomers and can only be interconverted by bond cleavage.

Reducing Properties of Monosaccharides

Monosaccharides with a free anomeric hydroxyl group can act as reducing agents.
Free anomeric OH groups can readily interconvert between open-chain and cyclic forms, allowing the aldehyde to be oxidized.
This is the basis of the Fehling’s reaction, used in Clinitab® for measuring urine glucose levels.
Cyclic forms with a glycosidic bond do not exhibit reducing properties.

Disaccharides

Two monosaccharides linked by a glycosidic bond.
The glycosidic bond is formed between the anomeric carbon of one sugar and a hydroxyl group on the other sugar.

Disaccharide Types and Properties

Lactose: A reducing sugar found in milk.
Sucrose: A non-reducing sugar found in plants like sugarcane and sugar beet.
Trehalose: A non-reducing sugar found in insects.

Penicillins: Mechanism of Inactivation

Constant use of antibiotics can lead to bacteria developing resistance
Resistance is caused by the evolution of β-lactamases in bacteria
β-lactamases are enzymes that cleave β-lactam antibiotics, rendering them inactive

Overcoming Bacterial Resistance

Use a suicide inhibitor of β-lactamase called clavulanic acid to preserve antibiotic potency
Ex: Augmentin® (Amoxicillin + Clavulanic Acid)

Glucosaminoglycans

Linear heteropolysaccharides composed of repeating disaccharide units
Hyaluronan (Hyaluronic acid): Found in synovial joints, vitreous humor of the eye, extracellular matrix of cartilage and tendons
Chondroitin sulfate: Found in cartilage, tendons, ligaments, walls of the aorta
Keratan sulfate: Found in cornea, cartilage, bone, horns, hairs, hoofs, nails, claws

Heparin and Congeners

Heparin is a fractionated form of heparan sulfate used as an anticoagulant
Heparin has the highest negative charge density of any known biological macromolecule
Average molecular weight (MW) of heparin is 15,000
Low molecular weight heparin (LMWH) has an average MW of 4,500

Oligosaccharide Links in Glycoproteins

N-linked: Oligosaccharide attached to the amide nitrogen of asparagine residues
O-linked: Oligosaccharide attached to the hydroxyl oxygen of serine or threonine residues

Other Glycoconjugates

Saccharides conjugated with steroids
Digoxin (Digitalis): Cardiac-active glycoside extracted from foxglove, used to treat heart conditions (heart failure, atrial fibrillations), toxic at high doses

Lipopolysaccharides

Found on the surface of gram-negative bacteria
Recognized by vertebrate immune systems and trigger vigorous immune responses in bacterial infections

Oligosaccharide Recognition: Lectins

Lectins are proteins that bind carbohydrates with high affinity and specificity
Oligosaccharides often hydrogen bond to specific areas in the lectin

Diseases, Drugs, Diagnostics

Diseases associated with carbohydrates: Diabetes, bacterial infections, heart conditions, thrombosis, viral infections, gastro-duodenal ulcers, stomach cancer
Drugs: Penicillins, Augmentin®, Digoxin, Eptifibatide, heparin and LMWH
Diagnostics: Clinitab tablets, blood/urine glucose level testers (Dextrostix, Clinistix, Diastix, Tes-Tape, bG Chemstrips, One Touch System)

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Description

Explore the fascinating world of carbohydrates, including their classifications into monosaccharides, oligosaccharides, and polysaccharides. This quiz will test your knowledge on their structures, roles, and significance in energy generation and storage. Perfect for students looking to deepen their understanding of this essential biomolecule.