Answer
Carbohydrates: Polar Organic Compounds with Functional Groups
The molecules that contain carbon-hydrogen (C–H) bonds, include either an aldehyde or a ketone group, and possess multiple hydroxy (-OH) groups are classified as carbohydrates. These molecules are highly polar due to the presence of multiple oxygen-containing functional groups.
Definition: Carbohydrates are organic biomolecules composed of carbon, hydrogen, and oxygen, typically with a general formula of (CH2O)n. They contain either an aldehyde or ketone group, along with several hydroxyl groups, which make them highly polar and water-soluble.
1. Structural Characteristics
- Basic Elements: Composed primarily of carbon (C), hydrogen (H), and oxygen (O).
- Functional Groups: Contains either an aldehyde group (-CHO) or a ketone group (C=O).
- Hydroxy Groups: Contains multiple –OH groups bonded to carbon atoms.
- C–H Bonds: Carbon-hydrogen bonds contribute to the organic nature of the molecule.
2. Classification of Carbohydrates
- Monosaccharides: Simple sugars such as glucose, fructose, and galactose.
- Disaccharides: Formed from two monosaccharides, e.g., sucrose and lactose.
- Polysaccharides: Long chains of monosaccharides, e.g., starch, cellulose, glycogen.
3. Chemical Properties
- Polar Nature: Due to multiple hydroxyl groups and carbonyl group, these molecules are highly polar.
- Water Solubility: Most simple carbohydrates dissolve easily in water.
- Hydrogen Bonding: Capable of forming hydrogen bonds with water and other polar solvents.
- Reducing Properties: Aldose sugars (with an aldehyde group) can act as reducing agents.
4. Biological Importance
- Primary Energy Source: Glucose is a major energy source for cells via cellular respiration.
- Storage Molecules: Starch (in plants) and glycogen (in animals) store energy.
- Structural Role: Cellulose provides structural support in plant cell walls.
- Recognition and Signaling: Carbohydrates play roles in cell recognition and immune responses.
Conclusion: Molecules containing C–H bonds, an aldehyde or ketone group, and several hydroxyl groups are known as carbohydrates. Their highly polar nature makes them hydrophilic, chemically reactive, and biologically essential.