BIOS 111: 1/28/25

Introduction to Sugars

  • Sugars can exist in solution for years without forming disaccharides; they tend to break down into smaller molecules instead.

  • Disaccharides are formed when simple sugars (monosaccharides) are enzymatically linked in cells.

Disaccharide Formation

  • Formation process:

    • Removal of a water molecule occurs (loss of an oxygen and two hydrogens).

    • Two simple sugars (e.g., glucose and fructose) are linked by an oxygen through a glycosidic bond or laminosidic linkage.

  • Visual representation:

    • Simplified drawing can depict where lines cross to represent the bonds.

    • After removing water, one oxygen remains bonded to two carbons from the monosaccharides.

Common Disaccharides

  • Sucrose: Composed of glucose and fructose.

  • Lactose: Composed of glucose and galactose (an isomer of hexose).

  • Maltose: Composed of two glucose molecules linked together.

  • Importance of recognizing structural differences among isomers of sugars (e.g., glucose vs. galactose).

Polysaccharides

  • Definition: Polysaccharides are long chains (or polymers) of monosaccharides.

  • Key polysaccharides in biological systems:

    • Starch: Storage polysaccharide in plants.

    • Glycogen: Storage polysaccharide in animals, primarily found in the liver and muscle cells.

    • Cellulose: Structural component in plant cell walls.

Glycogen

  • Features:

    • Forms long chains of glucose for compact energy storage.

    • Stores excess glucose as glycogen when sugar intake is high.

    • Each glycochids (glucose units) can link via alpha (1,4) bonds and form branch points using 1,6 linkages, aiding efficient storage.

  • Illustration request: Draw a simplified cartoon version of glycogen highlighting linkages and branching structures.

Starch vs. Glycogen

  • Starch is comprised mainly of linear and branched glucose units but has fewer branches compared to glycogen.

  • Starch is digestible by humans (found in potatoes, etc.), while glycogen is a compact energy source.

Cellulose

  • Composed entirely of glucose, cellulose is non-branched and tightly packed.

  • Functions: Provides structural support in plant cell walls, serves as dietary fiber for humans.

  • Beta (1,4) linkages in cellulose make it indigestible due to the inability of human enzymes to break the bonds, promoting its role as fiber.

Enzyme Activity and Digestibility

  • Enzymes play a crucial role in linking monosaccharides through glycosidic bonds but cannot recognize certain linkages in cellulose.

  • Fiber cannot be absorbed and passes through the digestive system intact, contributing to gut health.

  • Some organisms can digest cellulose and release glucose (e.g., certain bacteria).

Lipids Overview

  • Lipids are built primarily from carbon and hydrogen, forming nonpolar hydrocarbons.

  • Importance: Serve as energy storage, structural components, and signaling molecules in cells.

  • Fatty Acids:

    • Long hydrocarbon chains with an acidic end.

    • Saturated Fats: Completely filled with hydrogen (solid at room temperature).

    • Unsaturated Fats: Contain one or more double bonds (liquid at room temperature).

Trans Fats

  • Result from hydrogenation processes that convert unsaturated fats into a solid state for longer shelf life.

  • Health Concerns: Associated with negative health implications, such as heart disease.

Triglycerides

  • Formed from three fatty acids linked to glycerol through ester bonds (formed by condensation reactions).

  • Most fat is stored in the body as triglycerides in adipose tissue, releasing free fatty acids into the bloodstream for energy when needed.

Phospholipids

  • Modified triglycerides consisting of two fatty acids and a phosphate group.

  • Heads are hydrophilic while tails are hydrophobic, essential components of cell membranes, forming bilayers in water.

Micelles and Fat Absorption

  • Micelles are structures that help emulsify fats, allowing for their absorption during digestion by surrounding lipid molecules with hydrophilic portions facing outwards.

  • Lipids must be solubilized into micelles to effectively mix with and be absorbed through the intestinal lining.