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Questions and Answers
What is the primary structure of disaccharides?
What is the primary structure of disaccharides?
What type of glycosidic bond is formed when the OH group on carbon-1 is above the glucose ring?
What type of glycosidic bond is formed when the OH group on carbon-1 is above the glucose ring?
Which of the following is NOT a function of polysaccharides?
Which of the following is NOT a function of polysaccharides?
Which statement accurately describes amylopectin?
Which statement accurately describes amylopectin?
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Which of the following polysaccharides is involved in providing structural support?
Which of the following polysaccharides is involved in providing structural support?
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What is the primary function of glucose 6-phosphate in cells?
What is the primary function of glucose 6-phosphate in cells?
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What type of structures do monosaccharides predominantly adopt in aqueous solutions?
What type of structures do monosaccharides predominantly adopt in aqueous solutions?
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Which of the following describes the relationship between reducing sugars and anomeric carbons?
Which of the following describes the relationship between reducing sugars and anomeric carbons?
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What are six-membered ring structures of monosaccharides called?
What are six-membered ring structures of monosaccharides called?
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Which configuration is characteristic of α-D glucopyranose?
Which configuration is characteristic of α-D glucopyranose?
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What occurs when monosaccharides are oxidized by mild oxidizing agents?
What occurs when monosaccharides are oxidized by mild oxidizing agents?
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What is the primary feature of β configuration in cyclic monosaccharides?
What is the primary feature of β configuration in cyclic monosaccharides?
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What defines a reducing sugar?
What defines a reducing sugar?
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What reaction forms hemiacetals and hemiketals in monosaccharides?
What reaction forms hemiacetals and hemiketals in monosaccharides?
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Which molecule is synthesized from β-D glucopyranose?
Which molecule is synthesized from β-D glucopyranose?
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Study Notes
Carbohydrates and Glycobiology
- Carbohydrates are the most abundant biomolecules on Earth
- Photosynthesis converts massive amounts of CO2 and H2O into cellulose and other plant products yearly.
- Sugars and starch are essential dietary staples, and their oxidation provides energy in non-photosynthetic cells.
- Carbohydrate polymers (glycans) act as structural and protective elements in cell walls (bacteria, plants, and animals)
- Additional carbohydrate polymers lubricate skeletal joints and are involved in cell recognition and adhesion.
- Complex carbohydrate polymers act as signals, directing the intracellular destination or metabolic fate of hybrid molecules (glycoconjugates).
Key Principles
- Carbohydrates can have multiple chiral carbons, influencing how they interact with other biomolecules.
- The specific arrangement around each carbon atom is crucial for carbohydrate function
- Monosaccharides are the building blocks of larger carbohydrate polymers
- Polysaccharides adopt 3-D structures of lowest energy, determined by covalent bonds, hydrogen bonds, charge interactions and steric factors.
- The sequence of complex polysaccharides arises from the properties of the enzymes responsible for their assembly.
- Storing low-molecular-weight metabolites as polymers prevents dramatic changes in osmotic pressure.
Functions of Carbohydrates in Living Systems
- Carbohydrates provide nutritional energy (storage - starch and glycogen, fuels - glucose), metabolic intermediates (fructose)
- Carbohydrates form structural components of nucleotides (ribose), plant cell walls (cellulose), bacterial cell walls (peptidoglycan), arthropod exoskeletons (chitin), animal connective tissues (glycosaminoglycans)
- Function in cells (information) such as recognition, communication (cell surface of eukaryotes), and regulating osmotic pressure in bacteria cells.
Chemistry of Carbohydrates
- Carbohydrates have the empirical formula (CH2O)n or Cn(H2O)n; n varies from 3 to 7 (commonly 5 and 6).
- Some may contain nitrogen (chitin), phosphorus, or sulfur.
- Carbohydrates are polyhydroxy aldehydes or ketones, meaning they contain many hydroxyl groups (at least two)
Classification of Carbohydrates
- Monosaccharides are single sugar units.
- Oligosaccharides contain two to ten monosaccharide units.
- Disaccharides consist of two monosaccharide units linked together.
- Polysaccharides are large polymers containing hundreds of monosaccharide units.
- Carbohydrates can combine with lipids to form glycolipids or with proteins to form glycoproteins.
Monosaccharides and Disaccharides
- Monosaccharides are the simplest carbohydrates.
- These are colorless, crystalline solids readily soluble in water, most have a sweet taste.
- Monosaccharides contain unbranched carbon chains with single bonds between all carbons. One carbon double bonds to oxygen (carbonyl group). Additional carbon atoms bond to hydroxyl groups
- Common monosaccharides have names ending with "-ose" and are classified as aldehydes (aldoses) or ketones (ketoses). Examples include trioses, tetroses, pentoses, and hexoses.
- Stereoisomerism (different spatial arrangements) in sugars is significant, as enzymes are rigidly stereospecific.
Isomers and Stereoisomers
- Isomers are molecules with the same molecular formula but different structural formulas (e.g., various arrangements of atoms)
- Stereoisomers are isomers that have the same structural formula but different spatial arrangements of atoms (e.g., mirror images).
Chiral Centers
- A chiral center is a carbon atom bonded to four different groups. Chiral molecules exist in stereoisomeric forms.
Stereoisomerism's Biological Significance
- Stereoisomerism in sugars is vital since enzymes strictly control the specific stereoisomer to function properly and catalyse different reactions.
Phosporylated Derivatives
- Glucose 6-phosphate and other phosphorylated sugars are stable at neutral pH and bear a negative charge. The charge prevents free glucose from freely entering and leaving cells, which restricts glucose metabolism and movement within cells.
Cyclic Structures of Monosaccharides
- In aqueous solution, monosaccharides commonly exist in cyclic forms (ring structures).
- The reaction involves covalent bonding of the carbonyl group to an oxygen on a hydroxyl group within the chain.
- The results are derivatives called hemiacetals or hemiketals..
Cyclization of Monosaccharides
- Fewer than 1% of monosaccharides are in an open-chain form; the predominant form is a cyclic ring.
- The reaction between a hydroxyl group on carbon 5 (or 6, depending on structure) and an aldehyde (or ketone, on carbon 2) group produces a cyclic structure.
α and β Anomers
- Cyclization creates an anomeric carbon (bonded to 2 oxygens).
- The orientation of the hydroxyl group on the anomeric carbon determines if it's an α or β form.
- The configuration (α or β) differs in the spatial orientation (Fischer and Haworth) of the hydroxyl group on the anomeric carbon.
Pyranoses and Furanoses
- Six-membered ring structures are called Pyranoses.
- Five-membered ring structures are called Furanoses.
Polysaccharides
- Polysaccharides consist of many linked monosaccharides,.
- Homopolysaccharides are composed of one type of monomer. Examples include glycogen, starch, and cellulose.
- Heteropolysaccharides are formed from diverse monomers and play structural roles. Examples include peptidoglycans and glycosaminoglycans (GAGs).
- Polysaccharides don't have defined lengths or weights compared to proteins.
- Polysaccharide synthesis is driven by the enzymes that catalyze polymerization
Functions of Polysaccharides
- Storage: Glycogen in animals and starch in plants store glucose for energy.
- Structure: Cellulose provides structural support in plant cell walls, while chitin forms exoskeletons.
- Information: Polysaccharides, often linked to proteins or lipids, play roles in cell identification and communication.
Starches
- Starches are glucose polymers with two types:
- Amylose (15-20%): Linear, unbranched glucose chains linked by α-1,4 glycosidic bonds.
- Amylopectin (80-85%): Branched glucose chains linked by α-1,4 and α-1,6 glycosidic bonds.
Glycogen
- Animals store glucose as glycogen.
- Glycogen has a branched structure similar to amylopectin, but branches are shorter and more frequent, facilitating fast glucose mobilization.
Cellulose
- Cellulose is a linear polymer of glucose linked by β-1,4 glycosidic bonds.
- Cellulose forms straight, rigid fibers offering structural support to plant cell walls. Unlike starches, cellulose is indigestible to humans because of inability to break β-1,4 glycosidic bonds.
Dietary Fiber
- Cellulose and other non-digestible carbohydrates form dietary fiber.
- Benefits include promoting gut health, slowing digestion, aiding bowel function, reducing food intake, and reducing heart disease risk.
Peptidoglycans
- Peptidoglycans are heteropolymers fundamental to reinforcing bacterial cell walls.
- The repeating units of N-acetylglucosamine and N-acetylmuramic acid are cross-linked by short peptide chains.
Glycoconjugates
- Glycoconjugates combine carbohydrates with proteins (glycoproteins), lipids (glycolipids), or both.
- Glycoconjugates facilitate communication, cell-cell recognition, transport, and localization within the intracellular and extracellular environments.
- Glycoconjugates are involved in processes like cell signaling (e.g., growth factors), cell interaction, adhesion, and virus/bacteria recognition.
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Description
This quiz explores key concepts related to disaccharides and polysaccharides, focusing on their structures, functions, and types of glycosidic bonds. Test your understanding of amylopectin and the role of polysaccharides in structural support. Perfect for students delving into the world of carbohydrates in biochemistry.
