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What are osides?
Complex carbohydrates divided into two classes: holosides and heterosides
Holosides are formed by the association of sugar molecules, while heterosides (glycoconjugates) are formed by the association of sugars with non-carbohydrate molecules.
What are holosides?
Polymers formed exclusively of sugars or sugar derivatives linked by O-glycosidic bonds
Holosides consist of residues of sugars linked together, forming complex carbohydrates.
What are heterosides?
Glycoconjugates formed by the association of one or more sugars with a non-carbohydrate molecule
Heterosides include various types of molecules beyond just sugars.
Define glycosidic bond.
Covalent bond formed between the anomeric carbon of a sugar and a hydroxyl, amine, or thiol group of another molecule
Glycosidic bonds can be O-glycosidic, N-glycosidic, or S-glycosidic, depending on the type of group involved.
What happens to mutarotation when a glycosidic bond is formed?
Mutarotation ceases because the anomeric carbon’s configuration becomes fixed
The fixed configuration is used to define the type of glycosidic bond.
What is the difference between α and β glycosidic bonds?
α glycosidic bond has the anomeric carbon in the α position, while β glycosidic bond has it in the β position
This distinction affects the structure and properties of the resulting carbohydrate.
What are disaccharides?
Carbohydrates formed from 2 sugar residues linked by a glycosidic bond
Disaccharides include maltose, cellobiose, lactose, and sucrose.
How are oligosaccharides defined?
Carbohydrates composed of 3 to 20 sugar residues
Oligosaccharides can be linear or branched and are often linked to lipids or proteins.
What are polysaccharides?
Carbohydrates composed of more than 20 sugar residues
Polysaccharides can be homopolysaccharides or heteropolysaccharides.
What are reducing sugars?
Simple cyclic sugars that can reduce an oxidizing agent due to their free anomeric carbon
Examples of reducing sugars include maltose, cellobiose, and lactose.
What is a non-reducing sugar?
Sugar with no free anomeric carbon, involved in glycosidic bonds
Sucrose is an example of a non-reducing sugar.
What is the structure of α-amylose?
Linear polymer of glucose units linked by α(1→4) glycosidic bonds
α-amylose is slightly soluble in water and forms a helical structure.
What is glycogen?
Homopolymer of glucose that serves as a storage polysaccharide in animals
Glycogen has more branching than amylopectin, with branches occurring every 8 to 12 glucose residues.
What distinguishes cellulose?
Linear polymer of glucose linked by β(1→4) glycosidic bonds
Cellulose forms strong fibers due to hydrogen bonding between chains, making it insoluble in water.
Fill in the blank: The main component of the cell walls in plants is _______.
Cellulose
What is the function of starch in plants?
Storage polysaccharide composed of amylose and amylopectin
Starch is the most important carbohydrate in human nutrition.
True or False: All polysaccharides are linear.
False
Polysaccharides can be either linear or branched.
What are glycoproteins?
Proteins that have oligosaccharides covalently attached
Glycoproteins serve various functions, including cell recognition and signaling.
What is raffinose?
A trisaccharide found in vegetables, not digested by humans
Raffinose can be fermented by bacteria in the intestine, producing gas.
What type of linkage is found in cellulose?
β(1→4) glycosidic linkages
Cellulose has straight chains that can form hydrogen bonds, providing mechanical strength.
What is the structural role of cellulose in plants?
It allows plants to grow up to 30 meters to seek light
Cellulose’s mechanical strength is crucial for the structural integrity of plants.
What is chitin and where is it found?
The main structural component of insect and crustacean exoskeletons
Chitin is also present in the cell walls of some fungi, algae, and yeasts.
What is the structural composition of chitin?
Linear polymer of N-acetyl-D-glucosamine residues linked by β(1→4) bonds
Chitin structurally resembles cellulose and exists in microfibrils.
Define heterosides.
Molecules formed by the association of sugars and non-carbohydrate substances called aglycones
Aglycones can include phenolic compounds, alkaloids, steroids, lipids, and proteins.
What are the two criteria for classifying glycoconjugates?
- Nature of aglycone
- Type of linkage (N-glycosidic, O-glycosidic, S-glycosidic)
Glycoconjugates can be glycolipids or glycoproteins based on the aglycone type.
What is peptidoglycan?
A compound composed of heteropolysaccharides linked to peptides in bacterial cell walls
Contains repeated units of N-acetylglucosamine and N-acetylmuramic acid.
What are glycosaminoglycans (GAGs)?
Polymers formed by repeating disaccharide units of an amino sugar and uronic acid
GAGs can have over 25,000 repeats and are negatively charged due to sulfate and carboxyl groups.
What is the significance of sulfate and carboxyl groups in GAGs?
They confer a strong negative charge to GAGs
This charge is important for their biological functions and interactions.
True or False: Polysaccharides have a well-defined molecular mass.
False
Polysaccharides exhibit microheterogeneity, meaning they can vary in size and composition within the same cell.
What is the first step in analyzing a glycoconjugate?
Release the aglycone part using enzymes like glycosidases
This is essential for further purification and analysis of the polysaccharide.
What methods can be used for the purification of polysaccharides?
- Precipitation
- Centrifugation
- Chromatography (exclusion, ion exchange, affinity)
Affinity chromatography is particularly effective for sugars using lectins as ligands.
How can the composition of a carbohydrate be determined?
By hydrolyzing the glycosidic bond and identifying residues using HPLC or gas chromatography
This allows for detailed analysis of the sugar components.
What advanced techniques are used to determine the composition and sequence of glycosidic residues?
Mass spectrometry (MS) and nuclear magnetic resonance (NMR)
These techniques provide detailed structural information about carbohydrates.
