Introduction to Carbohydrates

Carbohydrates Overview

• Most abundant biomolecules on Earth, serving as the primary energy source in non-photosynthetic cells.
• Empirical formula is (CH₂O); commonly referred to as saccharides.
• Sugars are water-soluble carbohydrates that taste sweet, and consist of polyhydroxy aldehydes or ketones.

Biological Importance

• Major energy source for many animals; glucose undergoes glycolysis and Krebs cycle for ATP production.
• Stored as glycogen in animals and starch in plants, serving as energy reserves.
• Carbohydrates act as intermediates in fat and protein biosynthesis.
• Regulate nerve tissues and provide energy for brain function.
• Associated with lipids/proteins to create antigens, receptor molecules, vitamins, and antibiotics.
• Form structural components, notably in plant cell walls and animal connective tissues.
• Facilitate biological transport and cell communication, and aid in the activation of growth factors.
• Fiber-rich carbohydrates help prevent constipation and modulate the immune system.

Sources of Carbohydrates

• Grain products: Leading source, high in starch.
• Starchy vegetables: Potatoes, yams, peas, and corn contain complex carbohydrates.
• Fruits: Contain natural sugars like glucose and fructose.
• Dairy: The only significant source of carbohydrates not derived from plants.

Stereoisomers

• Stereoisomers have the same molecular formula but differ in spatial arrangements and can be classified into:
  • Enantiomers: Nonsuperimposable mirror images (e.g., D-glucose vs. L-glucose).
  • Diastereomers: Non-mirror image isomers with different chemical properties (e.g., D-glucose vs. D-altrose).

Optical Isomerism

• Optical isomers can rotate plane-polarized light. Dextrorotatory (+) and levorotatory (-) designations are based on the direction of rotation.
• Mixture of equal D and L isomers yields no optical activity, known as a racemic mixture.
• Glucose is dextrorotatory, while fructose is levorotatory.

Ascorbic Acid (Vitamin C) Uses

• Essential for collagen formation; aids in hydroxylation of proline and lysine during collagen synthesis.
• Required for bone formation, tryptophan metabolism, reconversion of methemoglobin, and acts as an antioxidant.
• Treatment for scurvy, bacterial infections, and stomach ulcers. Deficiency leads to various health issues, including anemia and osteoporosis.

Disaccharides and Oligosaccharides

• Oligosaccharides are sugars with 2-10 monosaccharide units (general formula: Cₙ(H₂O)ₙ).
• Disaccharides: Formed from two monosaccharides (e.g., Maltose, Sucrose, Lactose).

Maltose

• Disaccharide formed from two alpha-D glucose units linked by an alpha-1,4 glycosidic bond (C₁₂H₂₂O₁₁).
• Reducing sugar; can undergo mutarotation and hydrolysis to yield glucose.
• Used in brewing and as a bulking agent in various food products; contributes to energy.

Isomaltose

• Similar to maltose but linked by an alpha-1,6 bond; also a reducing sugar.
• Can be metabolized for energy mainly through digestion of starch.

Lactose

• Known as milk sugar, a disaccharide made of glucose and galactose (C₁₂H₂₂O₁₁).
• Cannot be absorbed until hydrolyzed by the lactase enzyme.
• Used in modified milk preparations and nutritional supplements for infants; helps mineral absorption and is utilized in pharmaceutical products.

Sucrose

• Commonly known as table sugar, formed from glucose and fructose; classified as a non-reducing sugar.
• Chemical properties include combustion to yield CO₂ and H₂O, and reaction with chloric acid to produce HCl and CO₂.

This quiz covers the fundamental concepts of carbohydrates, their classification, and their significance as biomolecules. Learn about their chemical structure, types, and the role they play in energy yield in non-photosynthetic cells. Explore the properties and definitions associated with sugars and saccharides.