Chemistry of Life

Chemistry of Life

  • AP Biology Exam Content

    • 8-11% of exam questions cover Chemistry of Life.

Water and the Elements of Life

  • Chemical Composition of Water

    • Water consists of two hydrogen molecules (H) covalently bonded to an oxygen molecule (O).

    • Electron distribution: Oxygen atom pulls electrons, giving it a slightly negative charge and each hydrogen a slightly positive charge.

    • Polar Compounds: Molecules with distinct charges due to bond structure (like water).

  • Hydrogen Bonds

    • Weak bonds form between a proton in one molecule and an electronegative atom of another (water's hydrogen and oxygen).

    • Importance of polar nature: Allows water to act as a solvent, enabling the distribution of essential chemicals in organisms.

  • Cohesion and Adhesion

    • Cohesion: Tendency of similar molecules (water) to stick together due to hydrogen bonding.

    • Results in surface tension, allowing droplets to form and solid objects to float.

    • Adhesion: Attraction between dissimilar molecules (e.g., water and charged substances).

    • Responsible for capillary action: movement of liquid against gravity (critical in plants).

Elements Essential to Life

  • Key Elements: Carbon (C), Hydrogen (H), Nitrogen (N), Oxygen (O) make up 99% of living matter.

  • Carbon's Bonding Properties

    • Can form four bonds, allowing complexity in biological molecules.

    • Configuration possibilities: single, double, and triple bonds, creating varied structures.

    • Forms major biological macromolecules: carbohydrates, proteins, lipids, nucleic acids.

Macromolecules

  • Types of Macromolecules

    • Polymers: Composed of monomers (repeating units).

    • Examples:

      • Nucleotides (DNA), amino acids (proteins), and sugars (carbohydrates).

    • Lipids: Generally not polymers but considered macromolecules.

  • Formation of Macromolecules

    • Dehydration Synthesis: Covalent bond formation by removing water.

    • Hydrolysis: Breakdown of polymers into monomers by adding water.

    • Energy considerations: Synthesis requires energy storage, hydrolysis releases energy for cellular use.

Protein Structure and Function

  • Structure of Proteins

    • Composed of amino acids linked by covalent peptide bonds.

    • Amino Acids: 20 types, each with a unique R group affecting properties and functions.

    • Levels of Structure:

    • Primary: Amino acid sequence.

    • Secondary: Regular sub-structures (e.g., alpha helices and beta sheets).

    • Tertiary: Three-dimensional folding driven by R group interactions.

    • Quaternary: Complexes formed from multiple polypeptide chains.

    • Denaturation: Loss of structure due to pH or temperature changes, usually reversible.

Carbohydrates

  • Role: Immediate energy source and structural components.

  • General Formula: $(CH2O)n$ where $n$ indicates the number of repeating units.

  • Types:

    • Monosaccharides: Simple sugars (e.g., glucose).

    • Disaccharides: Two monosaccharides (e.g., sucrose) formed by glycosidic bonds.

    • Polysaccharides: Long chains of monosaccharides (e.g., starch, cellulose).

Lipids

  • Characteristics: Nonpolar, hydrophobic molecules including fats, phospholipids, and steroids.

  • Fats/Triglycerides Composition: Glycerol backbone with three fatty acid chains.

    • Fatty Acids:

    • Saturated: No double bonds, solid at room temperature.

    • Unsaturated: One or more double bonds, may be cis (kinked) or trans (linear).

DNA and RNA Structure

  • DNA: Includes nucleotides (sugar, phosphate, nitrogen base);

    • Strands: Antiparallel arrangement (3' to 5' and 5' to 3').

    • Base pairing: A-T (or A-U in RNA), G-C using hydrogen bonds.

  • RNA: Similar to DNA but uses ribose and uracil instead of thymine; generally single-stranded.