Comprehensive College Biology Study Guide

The Science of Biology

• Definition of Biology: Biology is the scientific study of living organisms and their complex interactions with one another and their environments. It encompasses a vast array of subdisciplines including molecular biology, microbiology, neurobiology, zoology, and botany.
• Defining Science: Science is a rational attempt to describe and understand the nature of the universe.
      * Natural Sciences: Fields related to the physical world and its phenomena.
      * Basic Science: Research aimed at expanding the total knowledge base without immediate expectations for short-term practical application.
      * Applied Science: Research specifically designed to solve practical, real-world problems.
• Scientific Inquiry and Logic:
      * Inductive Reasoning: Moving from particular experimental results to produce general scientific principles.
      * Deductive Reasoning: Using general principles to predict specific results.
      * The Scientific Method: A structured, step-based process consisting of making observations, defining a problem, posing hypotheses, testing hypotheses with proper controls, and drawing conclusions.
• Communication of Results: Scientists publish their findings in peer-reviewed scientific journals. A typical research paper includes: Introduction, Materials and Methods, Results, and Concluding Discussion.
• Properties of Life: All living organisms share key properties: order, sensitivity/response to stimuli, reproduction, growth and development, regulation, homeostasis, and energy processing.
• Biological Hierarchy: Living things are organized into a hierarchy: Atoms $\rightarrow$ Molecules $\rightarrow$ Organelles $\rightarrow$ Cells $\rightarrow$ Tissues $\rightarrow$ Organs $\rightarrow$ Organ Systems $\rightarrow$ Organisms $\rightarrow$ Populations $\rightarrow$ Communities $\rightarrow$ Ecosystems $\rightarrow$ Biosphere.

The Chemical Foundation of Life

• Matter and Atoms: Matter has mass and occupies space. Atoms are the smallest units of an element ($92$ natural elements) and consist of protons, neutrons, and electrons.
• Chemical Bonds: Created through electron transfer or sharing molecules.
      * Strong Bonds: Covalent and Ionic bonds.
      * Weak Interactions: Hydrogen bonds and van der Waals interactions.
• Critical Properties of Water:
      * Solvency: Water is polar, allowing hydrogen bonds to form and polar molecules/ions to dissolve easily.
      * Heat Capacity: High heat capacity and high heat of vaporization ($540\,cal/g$) facilitate temperature stability and evaporative cooling (sweat).
      * Cohesion and Adhesion: Cohesion creates surface tension; adhesion allows capillary action.
• pH and Buffers: pH measures the concentration of hydrogen ions $[H^+]$. Acids decrease pH, while bases increase it. Buffers (like the human bicarbonate system) moderate pH changes.
• Carbon: Carbon is unique due to having four electrons in its outermost shell, enabling it to form four covalent bonds. It forms the backbone of organic molecules in chains or rings, often modified by functional groups.

Biological Macromolecules

• Synthesis and Breakdown:
      * Dehydration/Condensation: Monomers join to form polymers with the release of a water molecule ($H_2O$); requires energy.
      * Hydrolysis: Polymers are broken down into monomers using water; releases energy.
• The Four Major Classes:
      * Carbohydrates: Monosaccharides (glucose, fructose), disaccharides (sucrose, lactose), and polysaccharides (starch, glycogen, cellulose, chitin). Linked by glycosidic bonds.
      * Lipids: Nonpolar, hydrophobic. Types include triglycerides (fats/oils), phospholipids (membrane matrix), and steroids (cholesterol, hormones). Saturated fats have single bonds; unsaturated have one or more double bonds.
      * Proteins: Composed of amino acid monomers linked by peptide bonds to form polypeptides. Four structural levels: Primary (sequence), Secondary ($\alpha$-helix, $\beta$-pleated sheet), Tertiary (3D shape), and Quaternary (multiple chains).
      * Nucleic Acids: DNA and RNA. Nucleotides consist of a pentose sugar, a nitrogenous base (A, T, C, G, U), and a phosphate group. DNA is double-helical; RNA is typically single-stranded.

Cell Structure and Function

• Prokaryotic Cells: Domains Bacteria and Archaea. Characteristics: single-celled, no nucleus, DNA in nucleoid, lack membrane-bound organelles. Diameter range: $0.1$ to $5.0\,\mu m$.
• Eukaryotic Cells: Contain a membrane-bound nucleus and specialized organelles.
      * Nucleus: Houses DNA; nucleolus is where ribosomes are assembled.
      * Mitochondria: Site of cellular respiration and ATP production.
      * Endomembrane System: Nuclear envelope, Lysosomes (digestion), Vesicles, Endoplasmic Reticulum (RER for protein modification, SER for lipids/detox), and Golgi apparatus (sorting/tagging).
      * Cytoskeleton: Microfilaments (actin), Intermediate filaments (tension bearing), and Microtubules (transport tracks and chromosome movement).
• Plant vs. Animal Cells: Plants have cell walls (cellulose), chloroplasts (photosynthesis), and a large central vacuole. Animals have centrosomes and lysosomes.
• Cell Connections: Animal cells use tight junctions, desmosomes, and gap junctions. Plant cells use plasmodesmata.

Metabolism and Energy

• Bioenergetics: The study of energy flow through living systems.
• Metabolic Pathways:
      * Anabolism: Synthesis of complex molecules from simpler ones; requires energy input.
      * Catabolism: Breakdown of molecules into simpler ones; releases energy.
• Free Energy ($\Delta G$):
      * Exergonic Reactions: $\Delta G < 0$; spontaneous; releases energy.     * Endergonic Reactions: $\Delta G > 0$; non-spontaneous; consumes energy.
• Laws of Thermodynamics:
      * First Law: Total energy in the universe is constant; it cannot be created or destroyed.
      * Second Law: Every energy transfer involves loss as heat, increasing entropy (disorder).
• ATP (Adenosine Triphosphate): The primary energy currency. Energy is released when the terminal phosphoanhydride bond is hydrolyzed: $ATP + H_2O \rightarrow ADP + P_i + \text{free energy}$. Hydrolysis releases approximately $-7.3\,kcal/mol$.
• Enzymes: Protein catalysts that speed up reactions by lowering the activation energy ($E_A$). They bind substrates at the active site via an induced-fit mechanism. Regulated by pH, temperature, and inhibitors (competitive and allosteric).

Cellular Respiration and Photosynthesis

• Cellular Respiration Pathways:
      * Glycolysis: Occurs in cytoplasm. Net gain of $2\,ATP$ and $2\,NADH$ molecules per glucose.
      * Citric Acid Cycle (Krebs): Pyruvate converted to Acetyl-CoA. Cycle releases $CO_2$ and generates $NADH, FADH_2, \text{and } ATP/GTP$.
      * Oxidative Phosphorylation: Uses Electron Transport Chain (ETC) and chemiosmosis via ATP synthase. Oxygen ($O_2$) is the final electron acceptor, forming water ($H_2O$).
• Fermentation: Restores $NAD^+$ in the absence of oxygen to keep glycolysis moving. Includes lactic acid fermentation (muscles) and alcohol fermentation.
• Photosynthesis: Occurs in chloroplasts of photoautotrophs.
      * Light-Dependent Reactions: Occur in thylakoid membranes. Photons strike Photosystem II and I to produce $ATP$ and $NADPH$. Water is split, releasing $O_2$.
      * Calvin Cycle (Light-Independent): Occurs in stroma. Enzyme RuBisCO fixes $CO_2$ into organic G3P using $ATP$ and $NADPH$.

Cell Communication and Reproduction

• Signaling Types: Paracrine (local), Endocrine (long-distance via blood), Autocrine (self-signaling), and Direct (gap junctions).
• Receptors: Internal (bind small hydrophobic ligands like steroids) vs. Cell-surface (Ion channel-linked, G-protein-linked, Enzyme-linked).
• Signal Transduction: Cascades involve phosphorylation by kinases and second messengers (e.g., $Ca^{2+}, cAMP, IP_3$).
• Apoptosis: Programmed cell death to remove unnecessary or damaged cells.
• The Cell Cycle: Interphase ($G_1, S, G_2$) and Mitotic phase (Mitosis: Prophase, Prometaphase, Metaphase, Anaphase, Telophase; and Cytokinesis).
• Checkpoints: Three major regulators ensure completion and health ($G_1, G_2/M, \text{Metaphase}$). Breakdown of these leads to cancer.
• Meiosis: Two nuclear divisions resulting in four unique haploid nuclei. Key stages: Crossover (Prophase I) and Random Alignment (Metaphase I).

Genetics and Evolution

• Mendelian Inheritance: Laws of Segregation and Independent Assortment. Phenotype is the observable trait; Genotype is the underlying genetic map.
• Non-Mendelian Genetics: Incomplete dominance, Codominance, Multiple alleles, X-linked traits, and Epistasis (one gene masking another).
• DNA Structure: Anti-parallel double helix proposed by Watson and Crick. Bases pair: $A=T, G \equiv C$. Replication is semi-conservative.
• Evolution: Adaptation through mutation. Natural selection acts on variation. Speciation occurs via Allopatric (geography) or Sympatric (same habitat) pathways.
• Population Genetics: Hardy-Weinberg equilibrium describes a non-evolving population where frequencies are stable ($p^2 + 2pq + q^2 = 1$).
• Mechanisms of Change: Genetic drift (chance), Gene flow (migration), Mutation, and Selection (Stabilizing, Directional, Diversifying).