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Questions and Answers
What is the primary role of glucose in cellular metabolism?
Which carbohydrate is primarily used for energy storage in plants?
What distinguishes aldoses from ketoses?
What are oligosaccharides primarily composed of?
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Which of the following options describes a function of cellulose?
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Which part of the carbohydrate structure is primarily involved in forming glycoproteins?
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What is a characteristic feature of reducing sugars?
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How is glucose and fructose linked in sucrose?
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What characterizes aldoses among monosaccharides?
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Which of the following is an example of a ketose?
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What is true about the chirality of monosaccharides?
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What is the composition of the cyclization of monosaccharides?
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Hexose derivatives like glucose-6-phosphate have what characteristic?
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What is the role of glycosidic bonds in polysaccharides?
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What distinguishes epimers from other stereoisomers?
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Which of the following statements about D-fructose is incorrect?
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Study Notes
Carbohydrates: Structures & Functions
- Carbohydrates are organic molecules with the general formula (CH₂O)n.
- They are produced in plants through photosynthesis, using carbon dioxide and water to create carbohydrates and oxygen.
- Carbohydrates can range in size; the simplest is glyceraldehyde (a triose), and the largest is amylopectin, a highly branched polysaccharide with molecular weights over 200 million g/mol.
- They serve as energy sources, energy storage, structural components, and play informational roles in cell communication and immune responses.
Learning Outcomes
- Describe the structures of monosaccharides.
- Compare aldoses and ketoses.
- Differentiate between enantiomers, diastereomers, and epimers in monosaccharides.
- Understand the structure and properties of disaccharides.
- Recognize reducing sugars and distinguish them from non-reducing sugars.
- Explain the structure and functions of major polysaccharides like starch, glycogen, and cellulose.
- Describe glycoconjugates, focusing on glycoproteins and glycolipids.
Carbohydrate Classes
- Monosaccharides: Single sugar molecules containing an aldehyde group (aldoses) or a ketone group (ketoses).
- Disaccharides: Composed of two monosaccharide units linked by a glycosidic bond.
- Oligosaccharides: Chains of a few monosaccharide units (usually 3-10) linked together.
- Polysaccharides: Long chains (greater than 20 units) of monosaccharides, serving roles in energy storage and structural support.
Monosaccharides – Aldoses
- Aldoses contain an aldehyde group (-CHO) at the end of the molecule.
- They are classified based on the number of carbon atoms, such as 3C triose (glyceraldehyde), 4C tetrose (erythrose), 5C pentose (ribose), and 6C hexose (glucose).
- Aldoses are more common in nature than ketoses.
Monosaccharides – Ketoses
- Ketoses contain a ketone group (C=O) typically at the second carbon.
- Examples include dihydroxyacetone (a 3C triose) and fructose (a 6C hexose).
- D-fructose is the most common ketose in nature.
Stereochemistry of Monosaccharides
- All monosaccharides (except dihydroxyacetone) are chiral molecules, meaning they have at least one carbon atom bonded to four different groups.
- The number of stereoisomers a molecule can have is determined by the number of chiral centers (n), calculated by the formula 2^n.
- Enantiomers are mirror images that cannot be superimposed (e.g., D-glucose and L-glucose). The D- or L- configuration is determined by the configuration of the chiral center furthest from the carbonyl group.
- Epimers are monosaccharides that differ in configuration at only one carbon atom (e.g., D-glucose and D-galactose at C4).
Cyclization of Monosaccharides
- Monosaccharides with 5 or more carbons typically form cyclic structures in aqueous solutions.
- Hemiacetals form when an aldehyde reacts with an alcohol group, leading to ring closure.
- Hemiketals form when a ketone reacts with an alcohol group.
- D-glucose forms a six-membered ring structure known as pyranose.
- D-fructose forms a five-membered ring called furanose.
- The carbon atom that becomes the new chiral center during cyclization is called the anomeric carbon.
Hexose Derivatives
- Phosphate derivatives (e.g., glucose-6-phosphate) are crucial in glycolysis.
- Amino sugars (e.g., glucosamine and galactosamine) contain an amine group (-NH₂) replacing a hydroxyl group (-OH) and are important in structural polymers (e.g., bacterial cell walls).
Glycosidic Bonds
- A glycosidic bond is the linkage between two monosaccharide units.
- The bond is formed by the reaction of a hemiacetal or hemiketal group of one sugar with an alcohol group of another sugar.
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Description
Test your knowledge on the structures and functions of carbohydrates with this comprehensive quiz. Explore monosaccharides, disaccharides, and polysaccharides, and understand their roles in biological systems. Assess your understanding of important concepts such as aldoses, ketoses, and various types of sugars.
