CHEMICAL COMPOUNDS

Classification of Compounds

Chemical compounds in biological systems are classified as either inorganic or organic based on the presence of carbon atoms.

• Inorganic Compounds: Do not contain carbon (with exceptions such as CO2 and CO).

  • Examples: Water, salts, many acids and bases

• Organic Compounds: Contain carbon.

  • Examples: Carbohydrates, lipids, proteins, nucleic acids

Additional info: Organic compounds are typically larger and more complex than inorganic compounds and are essential for life processes.

WATER

Properties and Biological Importance

Water is the most abundant inorganic compound in living organisms and is vital for numerous physiological processes.

• High heat capacity: Water can absorb and release large amounts of heat with little temperature change, helping to stabilize body temperature.

• High heat of vaporization: Evaporation of water requires significant energy, which allows for effective cooling (e.g., sweating).

• Polarity: Water molecules are polar, making water an excellent solvent (the "universal solvent").

• Transport medium: Water facilitates the movement of substances in the body.

• Lubricant: Water reduces friction between body surfaces (e.g., in joints).

• Reactivity: Water participates in many chemical reactions, including hydrolysis and dehydration synthesis.

Example: Water dissolves ionic compounds like NaCl, allowing ions to be transported in blood and other fluids.

Water as the Universal Solvent

• Hydrophilic substances: Polar molecules that dissolve readily in water (e.g., salts, sugars).

• Hydrophobic substances: Nonpolar or amphipathic molecules that do not dissolve in water (e.g., oils, fats).

Additional info: The polarity of water enables it to form hydrogen bonds, which are critical for its solvent properties and for the structure of macromolecules.

BIOLOGICAL MACROMOLECULES

Elements and Types

Biological macromolecules are large, complex molecules essential for life. They always contain carbon (C), hydrogen (H), and oxygen (O), and may also contain nitrogen (N), phosphorus (P), and sulfur (S).

• Types:

  • Carbohydrates

  • Proteins

  • Lipids

  • Nucleic Acids

POLYMERS

Structure and Synthesis

Most biological macromolecules are polymers, which are long chains of repeating units called monomers.

• Monomer: The basic building block or repeating unit of a polymer.

• Polymer: A long molecule consisting of many monomers joined together.

Synthesis and Breakdown:

• Dehydration synthesis: Monomers are joined by the removal of a water molecule to form a polymer.

  • Equation:

• Hydrolysis: Polymers are broken down into monomers by the addition of water.

  • Equation:

Example: The formation and breakdown of sucrose (table sugar) involves dehydration synthesis and hydrolysis, respectively.

CARBOHYDRATES

Structure and Types

Carbohydrates are hydrophilic organic molecules composed of carbon, hydrogen, and oxygen, typically with the formula (CH2O)n, where n is the number of carbon atoms.

• Function: Serve as fuel (energy source) and have limited structural roles.

• Types:

  • Monosaccharides: Simple sugars, monomers of carbohydrates (e.g., glucose, fructose, galactose, ribose, deoxyribose).

  • Disaccharides: Composed of two monosaccharides joined by dehydration synthesis (e.g., sucrose, lactose, maltose).

  • Polysaccharides: Large, complex carbohydrates made of many monosaccharides (e.g., starch, glycogen, cellulose).

Monosaccharides

Monosaccharides are the simplest carbohydrates and serve as the monomers for more complex carbohydrates.

• Structure: Single-ring structures with 3-7 carbons.

• Examples:

  • Pentoses (5-carbon sugars): Ribose (C5H10O5), Deoxyribose (C5H10O4)

  • Hexoses (6-carbon sugars): Glucose (C6H12O6), Fructose (C6H12O6), Galactose (C6H12O6)

Additional info: Glucose is the primary energy source for most cells. Ribose and deoxyribose are components of RNA and DNA, respectively.

Disaccharides

Disaccharides are formed by joining two monosaccharides via a dehydration synthesis reaction.

Polysaccharides

Polysaccharides are large, complex carbohydrates with low solubility in water. They serve as energy storage or structural molecules.

• Starch: Storage form of glucose in plants.

• Glycogen: Storage form of glucose in animals (mainly in liver and skeletal muscle).

• Cellulose: Structural component in plant cell walls; not digestible by humans.

Glycogen Metabolism

• Glycogenesis: Formation of glycogen from glucose (anabolic process; decreases blood glucose).

• Glycogenolysis: Breakdown of glycogen to glucose (catabolic process; increases blood glucose).

• Gluconeogenesis: Formation of glucose from non-carbohydrate sources (e.g., amino acids, glycerol).

Additional info: These metabolic pathways are regulated by hormones such as insulin and glucagon.