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Biological Molecules Overview

Lactose Intolerance

  • Caused by a lack of the enzyme lactase, which breaks down the sugar lactose.

  • Lactase (an enzyme) is a protein; lactose (a sugar) is a carbohydrate.

Organic Compounds

  • Definition: Molecules primarily composed of carbon.

  • Carbon can bond up to four other atoms and form complex structures.

  • Hydrocarbons: Simplest organic compounds, made only of carbon and hydrogen.

    • Can form chains of various lengths (straight, branched, rings).

  • Isomers: Compounds with the same chemical formula but different structural arrangements.

Chemical Groups of Organic Compounds (Functional Groups)

  • The first five groups are hydrophilic (water-loving) and polar, making them soluble in water.

  • Hydroxyl Group: -OH

  • Carbonyl Group: C=O

  • Carboxyl Group: -COOH

  • Amino Group: -NH_2

  • Phosphate Group: -PO_4

  • Methyl Group: -CH_3

    • Nonpolar, hydrophobic, not reactive, but affects molecular shape and function.

Macromolecules

  • Definition: Large molecules (polymers) built from smaller, identical or similar building blocks (monomers).

  • Four main classes: Carbohydrates, Lipids, Proteins, Nucleic Acids.

  • Dehydration Reaction: Links monomers together to form polymers, removing a water molecule (H_2O).

  • Hydrolysis Reaction: Breaks polymers into monomers, adding a water molecule (H_2O).

  • Enzymes are specialized macromolecules (proteins) that catalyze (speed up) these reactions.

Carbohydrates

  • Monomers: Monosaccharides (simple sugars).

    • Examples: Glucose (C6H{12}O_6), Fructose, Honey.

    • Main fuel for cellular work, especially glucose.

  • Disaccharides: Two monosaccharides linked by dehydration reaction.

    • Examples: Sucrose (Glucose + Fructose), Maltose (Glucose + Glucose).

  • Polysaccharides: Many monosaccharides linked together.

    • Functions: Storage molecules or structural compounds.

    • Energy Storage: Starch (plants), Glycogen (animals).

    • Structural: Cellulose (plant cell walls), Chitin (fungi cell walls, insect exoskeletons).

    • Generally hydrophilic.

Lipids

  • Definition: Water-insoluble (hydrophobic) compounds; important for long-term energy storage.

  • Not typically built from monomers.

  • Fats (Triglycerides): Composed of one glycerol and three fatty acids, formed by dehydration reactions.

    • Saturated Fats: Maximum number of hydrogens, single bonds, straight chains, solid at room temperature (e.g., butter, meat fat).

    • Unsaturated Fats: Fewer hydrogens, one or more double bonds (causing kinks), liquid at room temperature (e.g., olive oil).

    • Trans Fats: Hydrogenated vegetable oils that pose significant health risks.

  • Phospholipids: Major component of cell membranes.

    • Structure: Glycerol head + phosphate group + two fatty acid tails.

    • Heads are hydrophilic, tails are hydrophobic, forming a phospholipid bilayer in water.

  • Steroids: Lipids with a carbon skeleton containing four fused rings.

    • Cholesterol: Common in animal cell membranes, precursor to other steroids (e.g., sex hormones).

    • Anabolic Steroids: Synthetic variants of testosterone; abuse leads to serious health consequences.

Proteins

  • Most diverse macromolecules with a wide range of structures and functions.

  • Monomers: Amino Acids (20 types).

  • Amino acids are linked by peptide bonds via dehydration reactions.

    • Two amino acids form a dipeptide; many form a polypeptide.

  • Enzymes: Proteins that act as biological catalysts, speeding up chemical reactions.

  • Denaturation: Alteration of a protein's shape (due to extreme heat, pH changes, high salt concentration), leading to loss of function.

  • Amino Acid Structure: Central carbon bonded to an amino group (-NH_2), a carboxyl group (-COOH), a hydrogen atom, and a unique R group.

    • The R group determines the amino acid's properties (hydrophobic/hydrophilic).

  • Four Levels of Protein Structure:

    • Primary Structure: The specific sequence of amino acids.

    • Secondary Structure: Coils (alpha helix) or folds (beta pleated sheets) formed by hydrogen bonds.

    • Tertiary Structure: Overall 3D shape resulting from interactions between R groups.

    • Quaternary Structure: (If applicable) Multiple polypeptide chains combine to form a functional protein.