Monosaccharides and Their Properties

Carbohydrates

• Carbohydrates are hydrates of carbon, often referred to as life's sweet molecules.
• They are fundamental components of living organisms, serving various functions including energy storage and structural support.
• Carbohydrates are classified into several types, including monosaccharides, disaccharides, oligosaccharides, and polysaccharides, based on the number of sugar units they contain.

Objectives

• Understanding the relationship between the structure and function of glucose is a key objective.
• Drawing the accurate molecular rings of glucose and fructose is also important.
• Distinguishing between alpha and beta anomers for both glucose and fructose is crucial.

Classes of Carbohydrates

• Monosaccharides are simple sugars (single sugar unit)
• Disaccharides are made up of two monosaccharides joined together.
• Oligosaccharides comprise three to nine monosaccharide units.
• Polysaccharides consist of many monosaccharide units joined into a long chain.

Monosaccharides

• Defining characteristics: The general formula for monosaccharides is (CH₂O)ₙ, where n ranges from 3 to 7.
• Types of Monosaccharides: Different monosaccharides exist depending on the number of carbon atoms (triose, tetrose, pentose, hexose).
  • Examples: D-glyceraldehyde, D-erythrose, D-ribose, D-fructose, D-glucose are some important monosaccharides.
• Functional Groups: Monosaccharides contain various functional groups, including hydroxyl (-OH) and carbonyl groups (aldehyde or ketone), which confer specific properties to the molecule.

Monosaccharides, Glucose

• Glucose has a crucial role: The chemical formula is C₆H₁₂O₆.
• Key Functional Groups: Glucose has an aldehyde group (carbonyl) and multiple hydroxyl groups (-OH).

Monosaccharides, Fructose

• Fructose is a ketohexose, with a different carbonyl group than glucose.
• Chemical structure: C₆H₁₂O₆.
• Functional Group: A ketone group and hydroxyl groups (–OH) are found in the chemical structure of fructose.

Monosaccharides, Continued

• Aldohexose and ketohexose have the same number of carbon atoms but differ in the carbonyl group.
• Monosaccharides are categorized based on the number of carbons and the type of carbonyl group.

Monosaccharides, Continued (Classification)

• Examples of Aldoses & Ketoses: Aldotriose (e.g., glyceraldehyde), aldotetrose, aldopentose, ketohexose (e.g., fructose).
• Glucose and fructose are both hexoses.

Monosaccharides, Continued (Stereoisomers)

• A chiral center is a carbon atom with four different groups attached to it.
• Glucose contains multiple chiral centers.
• Important: Stereochemistry (e.g., D- and L- isomers) is significant in biochemistry.

Monosaccharides, Continued (Multiple Chiral Centers)

• The number of stereoisomers for a molecule is determined by 2ⁿ, where n is the number of chiral centers.

Important Monosaccharides, Glucose

• Glucose is plentiful in nature and is crucial for energy production in cells.
• Glucose forms sucrose (table sugar) and lactose (milk sugar), along with polysaccharides.
  • Example polysaccharides: Glycogen, starch, and cellulose.

Important Monosaccharides, Fructose

• Fructose is the sweetest monosaccharide and is commonly referred to as fruit sugar.
• It's found in fruits, vegetables, and honey.
• Fructose forms sucrose, a common table sugar.
• Fructose is a structural isomer of glucose.

Oxidation and Reduction Reactions

• Aldehydes can be oxidized to carboxylic acids
• Aldehydes can be reduced to alcohols
• Benedict's test is used to detect the presence of reducing sugars (aldose sugars).

Ring Formation

• Carbonyl and hydroxyl groups react to form cyclic structures (hemiacetals) in monosaccharides.
• These cyclic forms are called pyranose (six-membered ring) or furanose (five-membered ring), and have alpha and beta anomers.

Ring Formation-Monosaccharide Structure

• Monosaccharides have both carbonyl and hydroxyl groups.
• These groups react to form hemiaacetals, giving rise to cyclic structures.
• The carbonyl group is planar, leading to different ring arrangements (alpha and beta anomers) around the anomeric carbon.

Monosaccharides, Pentoses

• Ribose and 2-deoxyribose are pentoses.
• They are components of nucleic acids (RNA and DNA).
• Ribose is found in RNA.
• Deoxyribose is found in DNA.
• Deoxyribose lacks an oxygen atom on carbon 2 compared to ribose.

Ring Formation– in glucose

• In six-membered pyranose rings of D-glucose, carbon 6 is always on the ring's exterior.
  • a anomer: trans configuration around anomeric carbon.
  • b anomer: cis configuration around anomeric carbon.

Ring Formation – in Fructose

• Fructose forms a five-membered furanose ring.
• Carbons 1 and 6 in a furanose structure are exterior to the ring.
• It also exists as alpha and beta anomers.

Section Summary

• Carbohydrates are classified as monosaccharides, disaccharides, oligosaccharides, and polysaccharides.
• A monosaccharide's formula is (CH₂O)ₙ (n=3-7).
• Most monosaccharides in nature are D-isomers.
• Important monosaccharides include glucose, galactose, fructose, ribose, and deoxyribose.
• The anomeric carbon is highly reactive.
• Monosaccharides act as reducing sugars, which means they can react with Cu²⁺ in a way that causes it to be reduced to Cu⁺.

Evaluation

• Identifying specific monosaccharide structures based on diagrams is needed.

Test your knowledge on monosaccharides, their structures, and functional groups. This quiz covers key concepts such as aldohexoses versus ketohexoses, stereoisomers, and the differences between various sugars. Perfect for students studying biochemistry or organic chemistry.