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Questions and Answers
Which of the following carbohydrates contains only one sugar unit?
What is the empirical formula for simple carbohydrates?
Which type of carbohydrate is formed from two monosaccharides?
Which of the following is NOT a biomedical importance of carbohydrates?
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Which of the following monosaccharides has a ketone group?
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Ribose and deoxyribose are important because they are components of:
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How many sugar units do oligosaccharides contain?
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Which of the following is a structural component of many organisms?
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Which of the following is the primary sugar found in blood?
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What property distinguishes dihydroxyacetone from other monosaccharides?
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Which chemical reaction results in the formation of gluconic acid from glucose?
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What do reducing sugars have that allows them to reduce cupric ions in reagents?
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Which monosaccharides can form osazone crystals?
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Which of the following pairs are epimers?
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Which statement about isomers is true?
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What is the major characteristic of sugars containing a free carbonyl group?
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Study Notes
Carbohydrate Chemistry
- Carbohydrates are organic compounds containing carbon, hydrogen, and oxygen
- The empirical formula for many simple carbohydrates is (CH2O)n
- Glucose is the most important carbohydrate
Classification of Carbohydrates
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Monosaccharides: Simplest carbohydrates containing one sugar unit.
- Examples: Glucose, fructose, galactose, and mannose
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Disaccharides: Two joined monosaccharides.
- Example: Maltose = Glucose + Glucose
-
Oligosaccharides: Contain 3-10 sugar units.
- Example: Maltotriose = 3 glucose
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Polysaccharides: Contain more than 10 sugar units.
- Examples: Starch and glycogen
Biomedical Importance of Carbohydrates
- 65% of our food should come from carbohydrates
- Major source of energy
- Cell membrane components (glycolipids and glycoproteins)
- Structural component of organisms:
- Cell walls of bacteria
- Fibrous cellulose of plants
- Degradation products used for synthesis of:
- Fatty acids
- Cholesterol
Monosaccharides
- Simplest units of carbohydrates
- General formula: CnH2nOn
- Cannot be hydrolyzed into simpler forms
Classification of Monosaccharides
-
Number of carbon atoms:
- Trioses (3 carbons), Tetroses (4 carbons), Pentoses (5 carbons), Hexoses (6 carbons)
-
Type of carbonyl group:
- Aldoses: Contain an aldehyde group as their carbonyl group
- Ketoses: Contain a ketone group as their carbonyl group
-
Presence of aldehyde or ketone groups and number of carbon atoms:
- Aldotrioses, Ketotrioses, Aldotetroses, Ketotetroses
Biomedical Importance of Monosaccharides
- Ribose and Deoxyribose (pentoses): Found in the structure of nucleic acids RNA and DNA
- Glucose (hexose): Most important sugar. Main sugar in blood and major source of energy
- Fructose (hexose): Main sugar of semen
- Xylulose (ketose): Intermediate in the hexose monophosphate pathway (HMP) and uronic acid pathway
Properties of Monosaccharides
-
Physical properties:
- Soluble in water, but insoluble in non-polar solvents
- Exhibit optical activity except for dihydroxyacetone
- Exist in α and β forms
Chemical Properties of Monosaccharides
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Oxidation: Oxidation of sugar produces acids (sugar derivatives).
- Oxidation of the aldehyde group (CHO → COOH) forms gluconic acid
-
Reduction: Reduction of sugar gives alcohols.
- D-glucose → D-sorbitol
- D-galactose → D-dulcitol
- D-fructose → D-mannitol + D-sorbitol
-
Reducing sugars:
- Sugars with free aldehyde or ketone groups can reduce other reagents.
- Reduce cupric ions Cu2+ (Fehling's and Benedict's reagents) into cuprous ions Cu+
- Used to detect sugar in the urine of diabetics
-
Osazone formation:
- Characteristic crystals formed from the reaction of sugars with phenylhydrazine.
- Sugars with free carbonyl groups form osazone crystals.
- Used to identify monosaccharides.
- Glucose, fructose, and mannose form needle-shaped crystals.
General Properties
-
Isomers: Compounds with the same chemical formula but different structures.
- Glucose, galactose, mannose, and fructose are isomers with the formula C6H12O6
-
Epimers: Two sugars that differ only in the configuration around one carbon atom.
- D-glucose and D-mannose are epimers, differing at C2.
- D-glucose and D-galactose are epimers, differing at C4.
- Note:* Galactose and mannose are NOT epimers.
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Description
Explore the fundamental concepts of carbohydrate chemistry in this quiz. Learn about the classification of carbohydrates, their structural importance, and their role in nutrition. Test your knowledge on monosaccharides, disaccharides, oligosaccharides, and polysaccharides.
