Carbohydrates Flashcards Quiz

Carbohydrates Overview

• Oligosaccharides consist of short chains of monosaccharides linked via glycosidic bonds; the most common are disaccharides (two monosaccharide units).
• Monosaccharides can be classified as aldoses or ketoses based on the position of the carbonyl carbon; aldoses have the carbonyl at the end, ketoses have it at any other position.

Monosaccharide Characteristics

• Glucose is an aldohexose, containing an aldehyde group and six carbon atoms.
• A monosaccharide with a ketone functional group and seven carbons is called a ketoheptose.
• Anomers are monosaccharides differing only at the hemiacetal carbon configuration.
• Cyclization of monosaccharides leads to ring structures through the formation of hemiacetals or hemiketals.

Glycosidic Bonds and Nonreducing Sugars

• When the anomeric carbon forms a glycosidic bond, the sugar becomes a nonreducing sugar due to the lack of free anomeric carbons.
• Proteins decorated with carbohydrates (glycoproteins) can be enriched in certain amino acids like Ser, Thr, and Asn for oligosaccharide attachment.

Polysaccharides

• Polysaccharides, also known as glycans, can be homopolysaccharides (same monosaccharide units) or heteropolysaccharides (different monosaccharide units).
• Cellulose features β-glycosidic linkages that create strong fibers through hydrogen bonding, while amylose forms helices through α-glycosidic linkages.

Glycosaminoglycans

• Glycosaminoglycans (GAGs) are linear polymers of repeating disaccharide units often found in the extracellular matrix.
• Hyaluronan, a type of GAG, consists of alternating D-glucuronic acid and N-acetylglucosamine residues and is important for tissue hydration.

Glycoproteins and Glycoconjugates

• Glycoproteins can have one or several oligosaccharides covalently linked, influencing their structure and function in biological processes.
• Glycoconjugates comprise carbohydrates linked to proteins or lipids, playing critical roles in cell recognition and signaling.

Special Terms and Functions

• Heparan sulfate is a GAG involved in various cellular processes, including binding to antithrombin to inhibit clot formation.
• Selectins mediate immunological functions and cell recognition, being found on the plasma membrane but are not intracellular.

Sugar Reducing Properties

• Nonreducing sugars do not have free anomeric carbons; trehalose, a disaccharide, is an example.
• Glycosidic linkages (like α1→4 in amylose and glycogen) determine the structure and properties of polysaccharides.

Summary of Key Functionalities

• Proteoglycans are macromolecules made of proteins and sulfated GAGs, important in extracellular interactions and stability.
• Antithrombin binding to heparan sulfate highlights the interplay between carbohydrates and protein functions in physiological processes.
• Distinction between homopolysaccharides and heteropolysaccharides is crucial in understanding their roles as structural or storage forms in biological systems.### Glycogen Structure and Function
• Glycogen has 28 branches, resulting in 29 nonreducing ends and 1 reducing end.
• Sugars are added primarily to nonreducing ends, facilitating rapid glucose storage and release.
• Glycogen's architecture allows simultaneous enzyme action on multiple branches, enhancing glucose availability.

Amylose vs. Cellulose

• Amylose and cellulose are both polysaccharides of D-glucose but differ in linkage types: cellulose with β(1→4), amylose with α(1→4).
• Cellulose forms stable, hydrophilic fibers due to hydrogen bonding, while amylose creates helical structures that exclude water.

Cellulose and Glycogen Comparisons

• Both consist of D-glucose; however, cellulose has β(1→4) linkages and is linear, while glycogen has α(1→4) linkages and is branched.

D-Glucose vs. D-Fructose

• Both sugars are hexoses; glucose is classified as an aldohexose, while fructose is a ketohexose.

Maltose vs. Sucrose

• Both are disaccharides; maltose consists of two α(1→4)-linked D-glucose units, while sucrose features α(1→2β)-linked D-glucose and D-fructose.

Hemiacetals and Glycosides

• Glycosides are formed when hemiacetals condense with alcohol.
• Hemiacetals arise from the condensation of an aldose with alcohol.
• Disaccharides contain glycosidic bonds, important for sugar classification.

Fructose and Temperature Effects

• Fructose can cyclize, favoring the furanose form at higher temperatures, leading to reduced sweetness in honey and corn syrup when heated.

Anomeric Forms of Sugars

• Sucrose has no free anomeric carbon, preventing mutarotation, while lactose exhibits two anomeric forms.

Reducing Sugars

• Reducing sugars include N-acetyl-glucosamine, D-lactose, and α-D-glucose due to their ability to donate electrons.

Glycoproteins vs. Proteoglycans

• Glycoproteins are located in Golgi complexes, secretory granules, and lysosomes, and contain high-affinity binding sites.
• Proteoglycans consist solely of sulfated glycosaminoglycan chains linked to serine and are found at the cell surface and in the extracellular matrix.

Heparin's Role as an Anticoagulant

• Heparin binds to antithrombin III, increasing its ability to inhibit coagulation by inducing conformational changes through interactions with positively charged residues.

Additional Terms

• Glucosyl: a univalent radical derived from the hemiacetal form of glucose.
• Lectin: a protein with high-affinity carbohydrate binding, facilitating cell-cell interactions, often involving oligosaccharides.

Test your knowledge of carbohydrates with this flashcard quiz focused on definitions and classifications such as disaccharides and oligosaccharides. Discover how these compounds are structured and their significance in biological systems.