Five Unifying Themes of Biology

Overview of Biological Unity and Diversity

• Core Theme: Evolution explains both the unity and diversity of life.

• Emergent Properties: New properties arise at each level of biological organization due to the arrangement and interactions of parts.

• Levels of Biological Organization: Ranges from molecules to the biosphere, including cells, tissues, organs, organisms, populations, communities, ecosystems, and the biosphere.

Genetics and Gene Expression

Gene Expression and Heredity

• Gene Expression: The process by which information from a gene is used to synthesize a functional gene product, often a protein.

• DNA vs. RNA: DNA stores genetic information; RNA is involved in protein synthesis and gene regulation.

Scientific Method and Experimental Design

Hypotheses, Theories, and Variables

• Experiments: Involve predictions, hypotheses, control variables, and independent & dependent variables.

• Hypothesis vs. Theory: A hypothesis is a testable statement; a theory is a well-substantiated explanation of some aspect of the natural world.

Chemistry of Life

Atoms, Elements, and Compounds

• Atoms: The basic unit of matter, composed of protons, neutrons, and electrons.

• Elements: Pure substances consisting of only one type of atom.

• Compounds: Substances formed from two or more elements chemically combined in fixed ratios.

• Subatomic Particles: Protons (positive), neutrons (neutral), electrons (negative).

• Atomic Number: Number of protons in an atom.

• Mass Number: Sum of protons and neutrons.

• Periodic Table: Organizes elements by increasing atomic number and recurring chemical properties.

• Valence Electrons: Electrons in the outermost shell, important for chemical bonding.

Chemical Bonds and Water

• Types of Chemical Bonds:

  • Covalent Bonds: Atoms share electrons; can be polar (unequal sharing) or nonpolar (equal sharing).

  • Ionic Bonds: Transfer of electrons from one atom to another, resulting in charged ions.

  • Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., oxygen or nitrogen).

• Properties of Water: High specific heat, cohesion, adhesion, excellent solvent, less dense as a solid.

• Acids and Bases: Acids donate H+ ions; bases accept H+ ions. pH scale measures acidity/basicity.

• Significance of Stanley-Miller Experiment: Demonstrated that organic molecules could be synthesized abiotically under early Earth conditions.

Organic Molecules and Isomerism

Organic Molecules and Isomers

• Organic Molecules: Contain carbon and hydrogen; form the basis of life.

• Isomers: Molecules with the same molecular formula but different structures. Types include structural, cis-trans, and enantiomers.

Macromolecules

Classes and Functions

• Four Classes: Carbohydrates, lipids, proteins, nucleic acids.

• Monomers and Polymers: Monomers are building blocks; polymers are long chains of monomers.

• Dehydration Synthesis: Joins monomers by removing water.

• Hydrolysis: Breaks polymers into monomers by adding water.

• Saturated vs. Unsaturated Fats: Saturated fats have no double bonds; unsaturated fats have one or more double bonds.

• Protein Structure: Primary (sequence), secondary (alpha-helix, beta-sheet), tertiary (3D folding), quaternary (multiple polypeptides).

Cell Structure and Function

Cell Membranes and Transport

• Cell Membrane Structure: Fluid mosaic model; composed of a phospholipid bilayer with embedded proteins.

• Hydrophobic vs. Hydrophilic: Hydrophobic molecules repel water; hydrophilic molecules attract water.

• Passive Transport: Movement of substances across membranes without energy (diffusion, osmosis, facilitated diffusion).

• Active Transport: Movement against concentration gradient, requires energy (ATP).

• Tonicity: Describes the relative concentration of solutes (hypertonic, hypotonic, isotonic).

• Bulk Transport: Endocytosis (into cell) and exocytosis (out of cell).

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic Cells: Lack a nucleus and membrane-bound organelles (e.g., bacteria).

• Eukaryotic Cells: Have a nucleus and membrane-bound organelles (e.g., plants, animals, fungi, protists).

• Organelle Functions: Nucleus (genetic material), mitochondria (energy), chloroplasts (photosynthesis), endoplasmic reticulum (protein/lipid synthesis), Golgi apparatus (modification and transport), lysosomes (digestion).

• Plant vs. Animal Cells: Plant cells have cell walls, chloroplasts, and large central vacuoles; animal cells do not.

Endosymbiont Theory

Origin of Eukaryotic Organelles

• Endosymbiont Theory: Proposes that mitochondria and chloroplasts originated as free-living prokaryotes engulfed by ancestral eukaryotic cells.

• Evidence: Double membranes, own DNA, ribosomes similar to prokaryotes, replicate independently.

Key Table: Comparison of Prokaryotic and Eukaryotic Cells