Carbohydrates Quiz

Biomolecules - Carbohydrates

• Carbohydrates are biomolecules closely associated with living organisms
• They are components of coenzymes, antibiotics, bacterial cell walls, and mammalian cell membranes
• They provide energy through oxidation (in plants, animals, and humans)
• They supply carbon for building cell components
• They serve as stored chemical energy
• They are structural components of nucleic acids (ribose in RNA and deoxyribose in DNA)
• Various forms of cellulose make up materials like cotton and linen, and are also the basic component of wood

Carbohydrate Structure and Classification

• Carbohydrates are typically polyhydroxyaldehydes, polyhydroxyketones, or substances that yield these compounds through hydrolysis
• Classified as monosaccharides, disaccharides, oligosaccharides, or polysaccharides based on their structure

Monosaccharides

• Basic nomenclature: The number of carbon atoms in a carbohydrate plus the suffix "-ose". (e.g., three carbons = triose).
• Functional groups: All carbohydrates initially contain a carbonyl functional group. Aldose is a carbohydrate with aldehyde functionality; ketose is a carbohydrate with ketone functionality.
• Isomers: Monosaccharides can have different arrangements of their atoms, resulting in structural isomers like aldoses and ketoses.
• Chirality: Monosaccharides often have chiral carbon centers, leading to stereoisomers. D- and L- designations are determined based on the configuration of the chiral carbon farthest from the aldehyde or ketone group.
• Epimers: These diastereomers differ only in the configuration at one stereogenic center.
• Examples: Glucose, fructose, glyceraldehyde, ribose.

Cyclic Structures of Monosaccharides

• Hemiacetal and Hemiketal formation: Aldehydes or ketones react with an alcohol to create cyclic hemiacetals or hemiketals.
• Pyranoses and Furanoses: Cyclized monosaccharides can form six-membered rings (pyranoses) or five-membered rings (furanoses) according to ring strain and other factors. The orientation of the hydroxyl group at the anomeric carbon can be α or β.
• Haworth projections: These representations show the cyclic structure of a sugar in a flat, two-dimensional form, with substituents oriented above or below the ring.

Anomeric Carbons and Mutarotation

• Anomeric carbon: The carbon atom in the ring structure that was previously the carbonyl carbon (C=O) of the open-chain form. It is a new asymmetric center, because the group was not asymmetrical before cyclization.
• Anomers: α and β forms of the same sugar that differ in the configuration around the anomeric carbon.
• Mutarotation: The phenomenon where anomers interconvert in solution, shifting the equilibrium between the α and β forms.

Reactions of Monosaccharides

• Epimerization: Base-catalyzed reaction where a hydroxyl group at the carbon changes its configuration.
• Enediol formation: A reaction involving the formation of intermediates through keto-enol tautomerism, changing the configuration of the carbonyls.
• Reduction: Reduction of the carbonyl group of an aldose or ketose creates an alditol, an acyclic alcohol.
• Oxidation: Oxidation of an aldehyde group to produce an aldonic acid using mild or strong oxidizing agents, or using enzymes.
• Acylation: Adding acyl groups (organic groups containing a carbonyl) to form esters.
• Alkylation: Replacing hydroxyl groups with alkyl groups to form ethers
• Formation of glycosides: Replacing the anomeric alcohol on a carbohydrate with another alcohol, creating a glycoside.

Reducing and Nonreducing Sugars

• Reducing sugars: Monosaccharides or disaccharides that can reduce oxidizing agents by producing a hemiacetal group.
• Nonreducing sugars: Lack a free hemiacetal group present in an open-chain conformation and cannot reduce oxidizing agents.

Disaccharides

• Disaccharide Formation: The bond between two monosaccharides via a glycosidic linkage between one unit's anomeric carbon and the other unit's hydroxyl group.
• Examples: Maltose, Cellobiose, Lactose, Sucrose

Polysaccharides

• Polysaccharide Structure: Polymers of monosaccharides linked via glycosidic bonds.
• Types:
  • Storage: Amylose, Amylopectin, Glycogen
  • Structural: Cellulose, Chitin

Specific Examples

• Glycogen: A storage polysaccharide found in animals, structurally similar to amylopectin, with more frequent branching.
• Cellulose: A structural polysaccharide found in plants having linear chains of glucose connected via β-1,4 linkages. These chains align parallel to form rigid structures. Humans cannot break down cellulose.
• Starch: A storage polysaccharide in plants consisting of amylose and amylopectin. These provide energy storage.
• Gentiobiose: A disaccharide made from the linkage of two glucose monomers via β-glycosidic linkage.

Test your knowledge of carbohydrates with this quiz covering monosaccharides, disaccharides, and polysaccharides. Dive into concepts like mutarotation and diastereomers to see how well you understand these essential biomolecules.