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Questions and Answers
What are carbohydrates broadly defined as?
Polyhydroxy aldehydes or ketones and their derivatives.
Which of the following are functions of carbohydrates in cells? (Select all that apply)
Match the types of monosaccharides with their classification based on carbon atoms:
Tetroses = C4H8O4 Triose = C3H6O3 Pentoses = C5H10O5 Hexoses = C6H12O6
What is a monosaccharide?
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What is D-Glucose also known as?
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D-Galactose occurs freely in nature.
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Which sugar is the sweetest of all sugars?
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What happens during glucoside formation with D-Glucose?
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What does reducing power of sugars refer to?
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What phenomenon is observed when a monosaccharide is dissolved in water?
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Study Notes
Carbohydrates Definition
- Polyhydroxy aldehydes or ketones and their derivatives
- Composed of carbon, hydrogen, and oxygen
- Functional groups include hydroxyl groups
- "-ose" indicates sugar
Function of Carbohydrates in Cells
- Major source of energy
- Major structural component of plant cells
- Immediate energy in the form of glucose
- Reserve or stored energy in the form of glycogen
Classification of Carbohydrates
- Classified by the number of subunits
- Monosaccharides - Simple sugars
-
Oligosaccharides
- Disaccharides
- Trisaccharides
- Tetrasaccharides
- Polysaccharides - Complex sugars
Monosaccharides
- Simple sugars that cannot be hydrolyzed further
- Classified based on the number of carbon atoms and as aldoses or ketoses
Classification by Carbon Atoms
- Triose (C3H6O3) - Glyceraldehydes, Dehydroxy acetone, Erthrulose
- Tetroses (C4H8O4) - Erythrose, Threose, Ribulose
- Pentoses (C5H10O5) - Xylose, Ribose, Arabinose
- Hexoses (C6H12O6) - Glucose, Galactose, Mannose, Fructose
Monosaccharides - Hexoses
-
D-Glucose (dextrose) "Blood Sugar"
- Essential energy source for all body functions
- Also known as: Dextrose and Blood Sugar
- Component of each disaccharide
-
D-Galactose
- Seldom occurs freely in nature
- Binds with Glucose to form lactose (milk sugar)
- Converted to glucose for energy after absorption
-
D-Fructose (levulose) "Fruit Sugar"
- Sweetest of all sugars (1.5x sweeter than sucrose)
- Found naturally in fruits and honey
Steriochemistry
- Optical isomers (enantiomers) differ in the spatial arrangement of atoms around an asymmetric carbon atom
- Mirror images of each other
- D-form: H atom on carbon 2 is projected to the left, OH group to the right
- L-form: H atom on carbon 2 is projected to the right, OH group to the left
- Example: Glyceraldehyde has one asymmetric carbon (C2), existing in D and L forms
D-Aldoses with Three, Four, Five and Six Atoms
- Visual representation of the chemical structures of D-Aldoses
Properties of Monosaccharides
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Mutarotation: Optical rotatory power changes gradually when dissolved in water, reaching a constant value
- Example: D-glucose initially has a specific rotation of +112.2°, but this changes to +52.7° after 24 hours
- Occurs with pentoses, hexoses, and reducing disaccharides
-
Glucoside Formation: When D-glucose is treated with methanol and HCl, it forms a- and 6-D-glucosides
- These glucosides are not reducing sugars and do not exhibit mutarotation
-
Reducing Power: Sugars with free or potentially free aldehyde or ketone groups can reduce cupric copper to cuprous
- Reducing sugar + 2 Cu++ → oxidized sugar + 2Cu (cuprous)
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Oxidation/Reduction: Alcoholic OH, aldehyde (COH), or keto (C=O) groups can be oxidized to carboxyl groups with oxidizing agents
- Mild oxidant like BrHO: Oxidizes only the aldehyde to gluconic acid (monocarbonic)
- Strong oxidizing agent like Conc HNO3: Oxidizes both aldehyde or ketone groups to...
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