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Questions and Answers
What is the empirical formula of carbohydrates?
What is the empirical formula of carbohydrates?
Which carbohydrate is essential for storing energy in plants and animals?
Which carbohydrate is essential for storing energy in plants and animals?
Which of the following is a structural component found in arthropods?
Which of the following is a structural component found in arthropods?
What role does ribose play in biological systems?
What role does ribose play in biological systems?
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What is glucose primarily synthesized from in plants?
What is glucose primarily synthesized from in plants?
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What is the major metabolic fuel for most mammals?
What is the major metabolic fuel for most mammals?
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Which carbohydrate can be formed from the hydrolysis of polysaccharides?
Which carbohydrate can be formed from the hydrolysis of polysaccharides?
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Which type of carbon do all carbohydrates contain that affects their optical activity?
Which type of carbon do all carbohydrates contain that affects their optical activity?
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What defines an asymmetric carbon atom?
What defines an asymmetric carbon atom?
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What is the relationship between enantiomers?
What is the relationship between enantiomers?
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How many isomers does glucose have based on its 4 asymmetric carbon atoms?
How many isomers does glucose have based on its 4 asymmetric carbon atoms?
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Which is NOT a type of isomerism exhibited by sugars?
Which is NOT a type of isomerism exhibited by sugars?
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What characterizes D and L isomerism in carbohydrates?
What characterizes D and L isomerism in carbohydrates?
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What structural form do most glucose molecules take in solution?
What structural form do most glucose molecules take in solution?
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What is the term for the two distinct configurations formed by rotation about the anomeric carbon?
What is the term for the two distinct configurations formed by rotation about the anomeric carbon?
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What does the presence of asymmetric carbon atoms confer to a compound?
What does the presence of asymmetric carbon atoms confer to a compound?
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What configuration is the hydroxyl group in when it is below the plane of the ring?
What configuration is the hydroxyl group in when it is below the plane of the ring?
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What process allows carbohydrates to change between α and β configurations?
What process allows carbohydrates to change between α and β configurations?
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Which of the following is an example of an epimer of glucose?
Which of the following is an example of an epimer of glucose?
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In what position does the keto group appear in fructose?
In what position does the keto group appear in fructose?
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What are monosaccharides classified based on?
What are monosaccharides classified based on?
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What is the smallest monosaccharide with the general formula (CH2O)n?
What is the smallest monosaccharide with the general formula (CH2O)n?
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Which type of isomerism involves structural differences between aldehydes and ketones?
Which type of isomerism involves structural differences between aldehydes and ketones?
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What is the chemical formula for monosaccharides?
What is the chemical formula for monosaccharides?
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What type of sugar is a hexose?
What type of sugar is a hexose?
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What configuration is a carbohydrate in when the hydroxyl group attached to the anomeric carbon is above the plane of the ring?
What configuration is a carbohydrate in when the hydroxyl group attached to the anomeric carbon is above the plane of the ring?
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Which of the following structures is referred to as a pyranose?
Which of the following structures is referred to as a pyranose?
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What is mutarotation?
What is mutarotation?
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What is the anomeric carbon?
What is the anomeric carbon?
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Which of the following is true regarding the stability of the chair and boat forms of ring structures?
Which of the following is true regarding the stability of the chair and boat forms of ring structures?
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What type of carbohydrate has five carbons?
What type of carbohydrate has five carbons?
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What type of structure results from the reaction of aldehyde and ketone moieties with alcohol groups?
What type of structure results from the reaction of aldehyde and ketone moieties with alcohol groups?
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Study Notes
Carbohydrates
- Carbohydrates are organic compounds with the empirical formula Cn(H2O)n.
- They are aldehyde or ketone derivatives of polyhydric alcohols.
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Importance of carbohydrates:
- Energy storage (e.g., starch and glycogen).
- Structural components (e.g., cellulose in plants and chitin in arthropods).
- Ribose is a component of coenzymes (e.g., FAD, NAD) and the backbone of RNA.
- Deoxyribose is a component of DNA.
- Saccharides and their derivatives play roles in the immune system, fertilisation, preventing pathogenesis, blood clotting, lubrication, and development.
- Hydroxyl groups allow carbohydrates to interact with the aqueous environment and participate in hydrogen bonding.
- Carbohydrate derivatives can contain nitrogen, phosphate, and sulfur compounds.
- Carbohydrates can combine with lipids to form glycolipids or with proteins to form glycoproteins.
Glucose
- Glucose is the most important carbohydrate.
- Synthesized in plants from CO2 and water through photosynthesis and stored as starch or used to synthesize cellulose for plant cell walls.
- Animals acquire most of their carbohydrates from plants, but can synthesize them from amino acids.
- Most dietary carbohydrate is absorbed into the bloodstream as glucose, formed by the hydrolysis of dietary polysaccharides and disaccharides.
- Glucose is the major metabolic fuel for mammals, except ruminants, and a universal fuel for the fetus.
- Glucose is the precursor for all other carbohydrates in the body, including glycogen, ribose, deoxyribose, galactose, glycolipids, glycoproteins, and proteoglycans.
Isomerism in Carbohydrates
- Carbohydrates contain at least one chiral carbon, making them optically active.
- A chiral carbon atom is attached to four different atoms or chemical groups.
- Mirror images of a chiral molecule are called enantiomers or optical isomers.
- Isomers have the same molecular formula but different structural formulas.
- The number of isomers depends on the number of chiral centers in the molecule, following the formula: Number of isomers = 2n (where n is the number of chiral centers). For example, glucose has 4 chiral carbons, resulting in 24 = 16 isomers.
Types of Isomerism
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D and L isomerism: Carbohydrates exist in D or L conformations determined by the orientation of the hydroxyl group on the chiral carbon farthest from the carbonyl carbon. Most physiologically significant carbohydrates are in the D-conformation.
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Pyranose and furanose ring structures: Rings resemble pyran (six-membered) or furan (five-membered) derivatives, leading to pyranoses and furanoses respectively. Glucose predominantly exists in the pyranose form in solution.
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Alpha and beta anomers: The rings can open and close, leading to rotation around the anomeric carbon, creating α and β configurations of hemiacetals and hemiketals.
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Epimers: Isomers with different configurations of –OH and –H groups at carbons 2, 3, or 4. Important glucose epimers include mannose (carbon 2) and galactose (carbon 4).
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Aldose and ketose isomerism: Fructose and glucose have the same molecular formula but different structures due to the presence of a keto group in position 2 in fructose (C2 is the anomeric carbon) as opposed to an aldehyde group in position 1 in glucose (C1 is the anomeric carbon).
### Classification of Carbohydrates -
Monosaccharides: Simple carbohydrates that cannot be hydrolyzed to smaller units.
- Aldehydes or ketones with two or more hydroxyl groups.
- General chemical formula: (CH2O)n.
- Classified by the number of carbon atoms: trioses, tetroses, pentoses, hexoses, etc.
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Disaccharides: Formed by the condensation of two monosaccharides.
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Oligosaccharides: Short chains of monosaccharides.
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Polysaccharides: Long chains of monosaccharides.
### Monosaccharides -
Triose (3 carbons): Glyceraldehyde and Dihydroxyacetone
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Tetrose (4 carbons): Erythrose
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Pentose (5 carbons): Ribose, Ribulose, Xylulose
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Hexose (6 carbons): Glucose, Galactose, Mannose, Fructose
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Heptose (7 carbons): Sedoheptulose
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Nonose (9 carbons): Neuraminic acid (sialic acid)
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The aldehyde and ketone moieties of five and six-carbon carbohydrates spontaneously react with alcohol groups to form intramolecular semiacetals or hemiketals.
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This forms five- or six-membered rings.
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Five-membered rings are termed furanoses as they resemble furan, while six-membered rings are termed pyranoses as they resemble pyran.
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Fischer projection: A method of representing monosaccharides in a two-dimensional format.
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Haworth projection: A method of representing cyclic monosaccharides in a two-dimensional format.
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Chair and boat conformations: The most stable form of furanose and pyranose rings is the chair conformation.
- Axial: Constituents of the ring that project above or below the plane of the ring.
- Equatorial: Constituents of the ring that project parallel to the plane of the ring.
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Description
This quiz covers the essential aspects of carbohydrates, including their structure, importance, and roles in biological systems. Participants will learn about various carbohydrate types, such as glucose and their derivatives, and how they contribute to energy storage and structural components in organisms.
