Study Notes on Carbohydrates

Chemistry of Carbohydrates

Chemical Formula

  • The general chemical formula for carbohydrates is represented as C<em>x(H</em>2O)yC<em>x(H</em>2O)_y.

  • Carbohydrates are biological macromolecules that primarily consist of carbon (C), hydrogen (H), and oxygen (O) atoms arranged in a certain way:

    • They can also be classified based on their structure as:

    • Polyhydroxy aldehydes

    • Polyhydroxy ketones

Classification of Carbohydrates

Carbohydrates can be classified into several categories based on their structure:

  • Monosaccharides: Simple sugars that cannot be hydrolyzed further. Examples include:

    • Aldose: Glucose, Erythrose, Ribose, Glucoheptose, etc.

    • Ketose: Dihydroxyacetone, Erythrulose, Fructose, etc.

  • Disaccharides: Composed of two monosaccharide units.

    • Examples include:

    • Non-reducing sugars: Sucrose (composed of glucose + fructose)

    • Reducing sugars: Maltose (composed of glucose + glucose), Lactose (composed of galactose + glucose)

  • Oligosaccharides: Composed of 3-10 monosaccharide units. An example is Raffinose, which is composed of glucose, galactose, and fructose.

  • Polysaccharides: Composed of more than 10 monosaccharide units.

    • Divided into two main categories:

    • Homopolysaccharides: Composed of the same type of monosaccharide units (e.g., Starch, Glycogen, Cellulose)

    • Heteropolysaccharides: Composed of different types of monosaccharide units (e.g., Hyaluronic acid, Keratan sulfate, Chondroitin sulfate)

Asymmetric Carbon and Isomerism

  • Asymmetric Carbon: A carbon atom that is attached to four different atoms or groups of atoms.

  • Isomers: Compounds that have the same molecular formula but different structural arrangements, which lead to different properties.

    • Optical Isomers: Isomers that differ in the orientation of atoms in space and may rotate plane polarized light differently.

    • Stereoisomers: Isomers that have the same structural formula but differ in the arrangement of atoms.

  • The number of isomers is related to the number of asymmetric carbons (n) in a sugar and is calculated using the formula 2n2^n.

  • Optical Activity: Refers to the ability of a compound to rotate the plane of polarized light.

    • If a compound rotates light to the left, it is referred to as Levorotatory; if to the right, it is termed Dextrorotatory.

    • Example: D-fructose is characterized as Levorotatory.

  • Epimerism: A type of stereoisomerism where two sugars differ in configuration around just one specific asymmetric carbon.

    • Example: Galactose is an epimer of glucose.