Chapter2

Chapter 2: The Chemistry of Life

Introduction to Life at the Chemical Level

  • Biologists study life at multiple levels from atomic to organismal.

  • The chapter focuses on chemical interactions in living organisms.

  • Cells contain various chemicals that interact to produce life features.

Matter: The Building Blocks of Life

Definition of Matter

  • Matter occupies space and has mass.

  • Exists in three physical states:

    • Solid

    • Liquid

    • Gas

Chemical Elements

  • Chemical elements are fundamental building blocks of matter.

  • Elements cannot be broken down by ordinary chemical means.

  • Over 100 known elements; 92 occur naturally on Earth.

  • Only about 25 elements are essential for life.

    • Key elements: Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N) account for 96% of human body weight.

    • Trace elements are necessary in smaller amounts (e.g., Iron, Iodine).

The Periodic Table

  • Lists elements according to their characteristics.

  • Organizes elements based on atomic number, symbol, and atomic weight.

  • Includes bulk elements (most abundant) and trace elements.

Atoms: The Smallest Units of Matter

Structure of Atoms

  • Atoms consist of three types of subatomic particles:

    • Protons: positive charge, mass.

    • Neutrons: no charge, mass.

    • Electrons: negative charge, nearly no mass.

  • Protons and neutrons form the nucleus, while electrons orbit around it.

Atomic Number and Mass

  • Atomic number: number of protons (determines element).

  • Mass number: total number of protons and neutrons.

Isotopes

  • Isotopes: forms of an element with the same number of protons but different neutrons.

Electron Configuration and Chemical Bonding

  • Electrons dictate how an atom interacts with others.

  • Electrons occupy shells, with outermost shells influencing chemical properties.

  • Atoms will bond chemically to fill their electron shells (octet rule).

Types of Chemical Bonds

Ionic Bonds

  • Formed when atoms transfer electrons, resulting in charged ions.

  • Example: Sodium chloride (NaCl).

Covalent Bonds

  • Formed when atoms share electrons.

  • Types of covalent bonds:

    • Single bond (one pair of shared electrons).

    • Double bond (two pairs of shared electrons).

Water: The Foundation for Life

Structure of Water

  • Composed of 2 hydrogen atoms and 1 oxygen atom (H2O).

  • Water is polar due to unequal sharing of electrons.

Properties of Water

  • Cohesion: water molecules stick together.

  • Adhesion: water molecules cling to other substances.

  • High heat capacity: absorbs energy before changing states.

  • Ice floats due to lower density compared to liquid water.

  • Water is an excellent solvent (aqueous solutions).

pH Scale, Acids, and Bases

Acids and Bases

  • Acids: donate H+ ions (pH 0-7).

  • Bases: remove H+ ions (pH 8-14).

Buffers

  • Regulate pH in living systems by accepting or donating H+ ions.

Organic Molecules in Life

Definition

  • Organic molecules are primarily carbon and hydrogen-based.

Carbon Chemistry

  • Carbon's versatility due to its ability to form four covalent bonds.

Hydrocarbons

  • Simplest organic compounds; used for energy storage.

Biological Macromolecules

Types of Macromolecules

  • Carbohydrates (e.g., sugars, starches).

  • Proteins (e.g., enzymes, structural proteins).

  • Nucleic acids (e.g., DNA, RNA).

  • Lipids (e.g., fats, phospholipids).

Carbohydrates

  • Include simple sugars (monosaccharides) and complex forms (polysaccharides).

Proteins

  • Composed of 20 different amino acids; essential for metabolic activities.

  • Structure of proteins includes primary, secondary, tertiary, and quaternary levels.

Nucleic Acids

  • Store genetic information (DNA, RNA).

Lipids

  • Hydrophobic molecules important for energy storage, insulation, and cell membranes.