Carbohydrates: Aldoses and Ketoses

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Questions and Answers

What role does hyaluronic acid play in the body?

Structural component of cells

Lubrication of joints (correct)

Detoxification of substances

Cellular communication

Which of the following is a positive result for Molisch's test?

No color change

Brown precipitate forms

Green color appears

Violet ring at the junction of the two layers (correct)

Which compound is primarily detected by Benedict's test?

Aldehydes

Chitin

Glycosaminoglycans

Reducing sugars (correct)

What color changes indicate reducing sugar presence in Benedict's test?

Green to brick-red Signup and view all the answers

What is the primary principle behind Molisch's test?

Dehydration reaction of carbohydrates Signup and view all the answers

Which of the following compounds is involved in detoxification processes?

Gluconic acid Signup and view all the answers

What happens when concentrated sulfuric acid is added in Molisch's test?

It causes dehydration of carbohydrates Signup and view all the answers

The heated solution in Benedict's test must be maintained for how long?

3 minutes Signup and view all the answers

What type of disaccharide is maltose classified as?

Reducing sugar Signup and view all the answers

Which monosaccharides make up sucrose?

D-glucose and D-fructose Signup and view all the answers

What characterizes homopolysaccharides?

They consist of a single type of monosaccharide unit. Signup and view all the answers

What is the primary function of trehalose in insects?

Energy storage Signup and view all the answers

Which of the following is a storage polysaccharide found in plants?

Starch Signup and view all the answers

Which polysaccharide is formed by linking two galactose units along with glucose and fructose?

Stachyose Signup and view all the answers

How do polysaccharides primarily differ from each other?

In the type of glycosidic linkage Signup and view all the answers

Which of the following is a structural polysaccharide?

Cellulose Signup and view all the answers

Which sugar is classified as a ketohexose?

Fructose Signup and view all the answers

What is the maximum number of stereoisomers that can be formed by a monosaccharide with four chiral centers?

16 Signup and view all the answers

Which of the following sugars is an aldopentose?

Ribose Signup and view all the answers

Which monosaccharide exists in both straight chain and cyclic forms?

Fructose Signup and view all the answers

What determines whether a sugar belongs to D or L isomerism?

The orientation of the –OH group farthest from the carbonyl carbon Signup and view all the answers

Which structure is typical of cyclic monosaccharides with five membered rings?

Furan Signup and view all the answers

What is the smallest monosaccharide?

Dihydroxyacetone Signup and view all the answers

Which of the following sugars has one chiral center?

Dihydroxyacetone Signup and view all the answers

What property of monosaccharides allows them to dissolve in water?

Presence of hydroxyl groups Signup and view all the answers

Which reaction leads to the formation of alditols from carbohydrates?

Reduction with sodium borohydride Signup and view all the answers

What is the primary storage form of energy derived from carbohydrates in humans?

Glycogen Signup and view all the answers

Which property distinguishes reducing sugars from non-reducing sugars?

Presence of aldehyde or ketone groups Signup and view all the answers

Which carbohydrate is known to be insoluble in water but dissolves in ammoniacal solution of cupric salts?

Cellulose Signup and view all the answers

What is the result of the Benedict’s test when reducing sugars are present?

Solution turns orange-red or brick red Signup and view all the answers

What do carbohydrates primarily provide in terms of energy content?

4 KCal/gm Signup and view all the answers

What are osazones primarily formed from in carbohydrate chemistry?

Reaction with phenyl hydrazine Signup and view all the answers

What role do structural polysaccharides like cellulose and chitin play in organisms?

Structural support Signup and view all the answers

Which of the following is NOT a homopolysaccharide?

Agar Signup and view all the answers

What is the primary function of heteropolysaccharides in organisms?

Extracellular support Signup and view all the answers

Which component of agar is primarily used for electrophoretic separation?

Agarose Signup and view all the answers

What type of linkage does peptidoglycan contain that contributes to bacterial cell wall rigidity?

β(1→4) linkage Signup and view all the answers

Which polysaccharide forms a gel upon cooling when dissolved in hot water?

Agar Signup and view all the answers

What is the main function of lysozyme in the human body regarding bacteria?

Hydrolyze peptidoglycan Signup and view all the answers

Which of the following is a characteristic of heteropolysaccharides compared to homopolysaccharides?

Yield a variety of monosaccharides upon hydrolysis Signup and view all the answers

Study Notes

Classification of Sugars

Sugars are classified as aldoses (containing an aldehyde group) or ketoses (containing a ketone group) based on their functional groups.
Common monosaccharides include:
- Glyceraldehyde (aldotriose)
- Dihydroxyacetone (ketotriose)
- Ribose (aldopentose)
- Fructose (ketohexose)
The smallest monosaccharides are glyceraldehyde and dihydroxyacetone with three carbon atoms.

Structure of Monosaccharides

Monosaccharides can exist in straight-chain or cyclic forms, with five and six-membered rings being the most stable.
Cyclic structures arise from the formation of hemiacetals when a hydroxyl group reacts with a carbonyl group.

Chiral Centers and Isomerism

All monosaccharides except dihydroxyacetone contain chiral carbons, leading to optically active isomers (enantiomers).
Glyceraldehyde has one chiral center, while glucose has four, resulting in different stereoisomers.

D and L Isomerism

D and L configurations are based on the orientation of the -OH group farthest from the carbonyl carbon.
Sugars with the -OH group on the right are D-isomers; on the left, they are L-isomers. D-isomers are predominant in biological systems.

Anomers and Glycosidic Bonds

Monosaccharides with five or more carbons typically form cyclic structures.
The conversion to cyclic form creates an anomeric carbon, leading to reducing disaccharides like maltose and lactose due to the presence of a free anomeric carbon.

Polysaccharides

Polysaccharides consist of ten or more monosaccharide units, linked by glycosidic bonds.
Homopolysaccharides contain a single type of monosaccharide (e.g., starch, cellulose), while heteropolysaccharides comprise multiple types and serve various structural and functional roles.

Storage and Structural Polysaccharides

Storage polysaccharides like starch (in plants) and glycogen (in animals) serve as energy reserves.
Structural polysaccharides such as cellulose (plant cell walls) and chitin (exoskeleton of insects) provide support and protection.

Heteropolysaccharides

Heteropolysaccharides yield various monosaccharides upon hydrolysis and provide extracellular support.
Examples include agar, used in gels for culturing and DNA separation, and peptidoglycan, vital for bacterial cell wall structure.

Physical Properties of Carbohydrates

Carbohydrates are typically odorless, colorless crystalline solids at room temperature and are soluble in water while being insoluble in organic solvents.

Chemical Properties of Carbohydrates

Sugars can form osazones through reactions with phenyl hydrazine.
Oxidation converts reducing sugars into carboxylic acids.
Hydrolysis of glycosidic bonds leads to the formation of α and β isomers.
Glycosides form from the condensation of monosaccharides.

Functions of Carbohydrates

Primary energy source, providing 4 kcal/g.
Serve as storage reserves in the form of glycogen.
Non-digestible carbohydrates (e.g., cellulose) act as dietary fibers.
Serve as precursors for nucleic acids and other organic compounds.

Analytical Tests for Carbohydrates

Molisch’s Test detects carbohydrates using α-naphthol and concentrated H2SO4; a positive result is indicated by a violet ring.
Benedict’s Test identifies reducing sugars by changing color from green to brick-red when heated with Benedict’s solution, indicating the presence of free aldehyde or ketone groups.

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Description

This quiz explores the classification of sugars based on their carbon atom count and functional groups. It includes details on trioses, tetroses, pentoses, hexoses, and heptoses, covering both aldoses and ketoses. Test your understanding of these carbohydrates and their structures.