Carbohydrates are essential biomolecules involved in energy storage and structural components in nature.
Examples include sugars and wood, which is composed of carbohydrates.
Learning Outcomes
Types of carbohydrates: monosaccharides, disaccharides, and polysaccharides.
Understand DNL configuration and alpha/beta configurations.
Learn about different structural representations:
Fischer projection
Haworth projection
Chair conformation
Importance of glycosidic bonds in polysaccharides and glycosides.
Definition of Carbohydrates
General formula: Cₙ(H₂O)ₙ, indicating water molecules associated with carbon atoms.
Carbohydrates can be:
Aldehydes or Ketones
Contain hydroxy functional groups (alcohol groups).
A single carbohydrate unit is called a monosaccharide.
If an aldehyde is present: aldose
If a ketone is present: ketose
Classification of Monosaccharides
Defined by the number of carbon atoms:
Triose (3 C)
Tetrose (4 C)
Pentose (5 C)
Hexose (6 C)
Heptose (7 C)
Octose (8 C)
Structure of Simple Monosaccharides
Simplest sugars include:
Aldose (e.g., glyceraldehyde): Has an aldehyde group (CHO) at the top.
First carbon typically has one alcohol (OH) and one hydrogen (H).
Ketose (e.g., dihydroxyacetone): Has a ketone group (C=O) at the second carbon.
Dihydroxyacetone is non-chiral (no asymmetric carbon).
Chirality and Stereoisomers
Monosaccharides generally exhibit chirality (except dihydroxyacetone).
The number of stereoisomers increases with the addition of carbon atoms:
2^n rule: where n = number of chiral centers.
Example: for 4 carbons, there are 4 stereoisomers; for 5, there are 8, and so forth.
Tests for Aldose vs. Ketose
Silver Mirror Test: A test to differentiate between aldoses and ketoses.
Aldoses, like glucose, can reduce silver hydroxide to metallic silver, creating a shiny mirror effect in the test vessel due to oxidation.
Ketoses cannot undergo this oxidation, hence do not produce the mirror effect.
Conclusion
Understanding carbohydrates includes recognizing different forms, structural representations, and key characteristics, such as functional groups and chirality.
Mastery of these concepts is essential for further studies in biochemical pathways and nutrition.