General Biology: Foundations, Cell Structure, Water, Macromolecules, and Enzymes

Chapter 1: Foundations of Biology

Cell Theory

The cell theory is a fundamental concept in biology that describes the properties of cells, the basic unit of life.

• Pattern: All organisms are made of cells.

• Process: All cells come from preexisting cells.

• Historical context: Spontaneous generation (the idea that cells could arise from nonliving material) was disproven by experiments such as the straight neck and swan neck flask experiments.

• Example: In the swan neck flask experiment, no cells appeared in the broth unless the flask was exposed to outside air, supporting that cells arise from preexisting cells.

Theory of Evolution by Natural Selection

Evolution explains the diversity of life and is based on the idea that species change over time through natural selection.

• Pattern: Species are related by common ancestry.

• Process: Natural selection - characteristics of a population can be modified from generation to generation.

• Key points:

  1. Individuals have different (heritable) traits.

  2. Some individuals' differences make them more suitable for reproduction.

Chapter 2: Atoms, Bonds, and Molecules

Atomic Structure

Atoms are the basic units of matter, composed of protons, neutrons, and electrons.

• Electron: -1 charge

• Proton: +1 charge

• Atomic number: Number of protons

• Mass number: Protons + neutrons

Chemical Bonds

Atoms form bonds to achieve stable electron configurations.

• Ionic bonds: Attraction between positive and negative ions (involves transfer of electrons).

• Covalent bonds: Sharing of electrons between atoms.

• Nonpolar covalent bonds: Electrons are shared equally.

• Polar covalent bonds: Electrons are not shared equally; the more electronegative atom has a stronger pull.

• Electronegativity scale: O > N > C ≈ H (Important to memorize)

Chapter 3: Water and Its Properties

Hydrogen Bonds

Hydrogen bonds are weak attractions between the slightly positive hydrogen atom of one molecule and the slightly negative atom (often oxygen or nitrogen) of another molecule.

• Hydrogen bonds are responsible for many of water's unique properties.

Four Properties of Water

Water's unique properties make it essential for life.

• Versatility as a solvent: Water can dissolve many substances, especially polar or charged molecules.

• Cohesive properties: Water molecules stick to each other, resulting in high surface tension.

• Expansion when frozen: Water expands as it freezes, making ice less dense than liquid water.

• Ability to stabilize heat: Water has a high specific heat and high heat of vaporization, helping to moderate temperature changes.

Table: Properties of Water

Property	Description
Solvent	Dissolves polar and charged substances
Cohesion	Water molecules stick together
Expansion upon freezing	Ice is less dense than liquid water
Heat stabilization	High specific heat and heat of vaporization

Chapter 5: Biological Macromolecules

Biological Polymers

Macromolecules are large molecules made by joining smaller subunits (monomers) through condensation reactions.

• Condensation reaction: Joins monomers, releases water.

• Hydrolysis: Breaks polymers into monomers, uses water.

Proteins: Structure and Function

Proteins are polymers of amino acids and have diverse functions in cells.

• Amino acid structure: Central carbon, amino group, carboxyl group, hydrogen, and R group (side chain).

• Primary structure: Linear chain of amino acids.

• Secondary structure: Hydrogen bonds form alpha helices and beta sheets.

• Tertiary structure: Overall 3D shape, stabilized by hydrogen bonds, ionic bonds, hydrophobic interactions, van der Waals forces, and disulfide bridges.

• Quaternary structure: Multiple polypeptide chains combine.

• Example: Hemoglobin has quaternary structure; sickle cell disease results from a single amino acid change.

Table: Protein Structure Levels

Level	Structure	Example
Primary	Sequence of amino acids	Peptide chain
Secondary	Alpha helix, beta sheet	Fibrous proteins
Tertiary	3D folding	Enzymes
Quaternary	Multiple polypeptides	Hemoglobin

Chapter 6: Lipids and Membranes

Classes of Lipids

Lipids are hydrophobic molecules important for energy storage and membrane structure.

• Three classes: Fats, steroids, phospholipids

• Phospholipids: Amphipathic molecules with hydrophilic heads and hydrophobic tails; form bilayers in membranes.

• Fluidity: Determined by the types of fatty acids; unsaturated fatty acids increase fluidity, saturated decrease it.

Membrane Structure and Transport

Cell membranes are selectively permeable barriers composed of a phospholipid bilayer with embedded proteins.

• Diffusion: Movement of molecules from high to low concentration.

• Osmosis: Diffusion of water across a selectively permeable membrane.

• Hypertonic: Higher solute concentration outside the cell; water leaves the cell.

• Hypotonic: Lower solute concentration outside; water enters the cell.

• Isotonic: Equal solute concentration; no net water movement.

• Proteins in membranes: Integral (span the membrane) and peripheral (attached to surface).

• Transport proteins: Channels (passive), carriers (passive or active), pumps (active, require ATP).

• Example: Sodium-potassium pump moves Na+ out and K+ in, using ATP.

Enzymes and Metabolism

Enzyme Function

Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy.

• ΔG (Gibbs free energy): $\Delta G = G_{\text{products}} - G_{\text{reactants}}$

• Spontaneous reactions: $\Delta G < 0$ (energy released)

• Nonspontaneous reactions: $\Delta G > 0$ (energy required)

• Enzymes: Lower activation energy but do not change ΔG.

• Cofactors and coenzymes: Non-protein helpers (vitamins, minerals).

• Inhibitors: Competitive (bind active site), noncompetitive/allosteric (bind elsewhere, change enzyme shape).

• Denaturation: Extreme temperature or pH can denature enzymes.

Table: Types of Enzyme Inhibition

Type	Mechanism	Effect
Competitive	Binds active site	Blocks substrate
Allosteric	Binds elsewhere	Changes enzyme shape

Additional info: These notes provide a concise overview of foundational topics in general biology, including cell theory, evolution, atomic structure, water properties, macromolecules, membrane structure, and enzyme function, suitable for exam preparation.