Cumulative Biology Study Guide: Core Concepts from Chapters 1–16 & 26

1. The Science of Biology

Characteristics and Methods of Life

• Life Characteristics: All living things exhibit cellular organization, complexity, sensitivity to stimuli, growth and reproduction, energy use, homeostasis, and evolutionary adaptation.

• Biological Hierarchy: Atoms → molecules → organelles → cells → tissues → organs → organ systems → organisms → populations → ecosystems → biosphere.

• Scientific Method: Involves observation, hypothesis formation, experimentation, data collection, and drawing conclusions. Hypotheses must be testable and falsifiable.

• Theory vs. Law: A theory is a well-supported, interconnected explanation; a law describes consistent natural phenomena.

• Homeostasis: The maintenance of stable internal conditions.

2. The Chemical Context of Life

Atoms, Bonds, and Water

• Atoms: Composed of protons, neutrons, and electrons. Atomic number = number of protons; mass number = protons + neutrons.

• Isotopes: Atoms of the same element with different numbers of neutrons.

• Ions: Charged atoms due to loss/gain of electrons.

• Chemical Bonds:

  • Ionic: Transfer of electrons (e.g., NaCl).

  • Covalent: Sharing of electrons; can be polar (unequal sharing) or nonpolar (equal sharing).

  • Hydrogen Bonds: Weak attractions between polar molecules (e.g., between water molecules).

  • Van der Waals: Weak, transient interactions.

• Water Properties: Cohesion, adhesion, high specific heat, high heat of vaporization, excellent solvent, density anomaly (ice floats), hydrophobic interactions.

• pH Scale: Measures hydrogen ion concentration; acids donate H+, bases accept H+. Buffers stabilize pH.

• 2-8-8 Rule: Electron shell configuration (first shell: 2, second: 8, third: 8 electrons).

3. Carbon and the Molecular Diversity of Life

Organic Molecules and Functional Groups

• Carbon: Forms four covalent bonds, allowing for diverse organic molecules.

• Functional Groups: Specific groups of atoms (e.g., hydroxyl, carboxyl, amino, phosphate) that confer properties to organic molecules.

• Connection to Bonds: Carbon's bonding capacity underlies the structure of all biological macromolecules.

4. Water and Life

Water’s Role in Biology

• Polarity: Water is polar, leading to hydrogen bonding.

• Cohesion & Adhesion: Cohesion (water to water), adhesion (water to other substances).

• Acids/Bases & pH: pH scale (1–14); 7 is neutral. Acids have pH < 7, bases > 7.

5. The Structure and Function of Large Biological Molecules

Macromolecules

• Carbohydrates: Monosaccharides (e.g., glucose), disaccharides, polysaccharides (starch, glycogen for storage; cellulose, chitin for structure).

• Lipids: Triglycerides (saturated/unsaturated), phospholipids (form bilayers), steroids, waxes. Not true polymers.

• Proteins: Made of 20 amino acids linked by peptide bonds. Four levels of structure: primary (sequence), secondary (α-helix, β-sheet), tertiary (3D folding), quaternary (multiple polypeptides). Denaturation disrupts structure.

• Nucleic Acids: DNA and RNA made of nucleotides (A, G = purines; C, U, T = pyrimidines). ATP is the energy currency.

6. A Tour of the Cell

Cell Structure and Function

• Prokaryotes: No nucleus, circular DNA, no membrane-bound organelles. Bacteria and Archaea.

• Eukaryotes: Nucleus, membrane-bound organelles (mitochondria, chloroplasts, ER, Golgi, etc.).

• Plant Cells: Unique features include chloroplasts, central vacuole, and cell wall (cellulose).

• Cell Walls: Plants (cellulose), fungi (chitin), bacteria (peptidoglycan).

• Cell Junctions: Tight, adhesive, gap junctions (animals); plasmodesmata (plants).

7. Membrane Structure and Function

Membranes and Transport

• Fluid Mosaic Model: Membrane composed of phospholipids, proteins, cholesterol.

• Transport Mechanisms:

  • Passive: Diffusion, osmosis, facilitated diffusion (channels/carriers).

  • Active: Requires ATP (e.g., Na+/K+ pump, coupled transport).

  • Bulk Transport: Endocytosis (phagocytosis, pinocytosis, receptor-mediated), exocytosis.

• Tonicity: Hypertonic, hypotonic, isotonic solutions affect cell water balance.

8. An Introduction to Metabolism

Energy, Enzymes, and Metabolic Pathways

• First Law of Thermodynamics: Energy cannot be created or destroyed.

• Second Law: Entropy (disorder) increases in spontaneous processes.

• Free Energy (ΔG): $\Delta G = \Delta H - T\Delta S$; negative ΔG = spontaneous.

• Enzymes: Biological catalysts that lower activation energy, have specificity, and can be regulated (competitive/noncompetitive inhibitors, allosteric regulation, cofactors/coenzymes).

• ATP Cycle: $\mathrm{ATP} \rightarrow \mathrm{ADP} + \mathrm{P_i}$ releases energy.

9. Cellular Respiration and Fermentation

Harvesting Chemical Energy

• Aerobic Respiration Stages:

  1. Glycolysis (cytosol): 1 glucose → 2 pyruvate, 2 ATP, 2 NADH.

  2. Pyruvate Oxidation (mitochondrial matrix): → acetyl-CoA, NADH, CO2.

  3. Citric Acid Cycle: acetyl-CoA → 3 NADH, 1 FADH2, 1 ATP, CO2.

  4. Electron Transport Chain & Chemiosmosis (inner mitochondrial membrane): Proton gradient drives ATP synthase.

• Total ATP Yield: ~36–38 ATP per glucose.

• Anaerobic Respiration: Fermentation regenerates NAD+ (produces lactate or ethanol).

• Regulation: ATP and NADH inhibit key enzymes (feedback inhibition).

10. Photosynthesis

Converting Light Energy to Chemical Energy

• Overall Equation: $6\mathrm{CO}_2 + 6\mathrm{H}_2\mathrm{O} + \text{light energy} \rightarrow \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 + 6\mathrm{O}_2$

• Light Reactions (thylakoid): Photosystems II & I, water splitting → O2, ATP, NADPH.

• Calvin Cycle (stroma): Carbon fixation (Rubisco), reduction (G3P), regeneration of RuBP.

• Photorespiration: Rubisco uses O2 instead of CO2, wasting carbon; C4 and CAM plants have adaptations to minimize this.

11. Cell Communication

Signaling Mechanisms

• Signal Types: Direct contact, paracrine, autocrine, endocrine, synaptic.

• Receptors: Intracellular (e.g., steroid hormones), cell-surface (ion channels, enzyme-linked receptors, GPCRs).

• Second Messengers: cAMP, IP3, DAG, Ca2+.

• RTKs: Dimerization → autophosphorylation → kinase cascades (e.g., MAPK pathway).

• GPCRs: Activate G proteins, which then activate effector enzymes.

12. The Cell Cycle

Cell Division and Regulation

• Phases: G1, S, G2, M (mitosis); checkpoints at G1/S, G2/M, and spindle assembly.

• Regulation: Cyclin-dependent kinases (Cdks) and cyclins; MPF triggers mitosis.

• Mitosis Phases: Prophase, prometaphase, metaphase, anaphase, telophase, cytokinesis.

13. Meiosis and Sexual Life Cycles

Genetic Variation

• Meiosis I: Homologous chromosomes separate; crossing over and independent assortment increase genetic diversity.

• Meiosis II: Sister chromatids separate.

• Products: Four genetically distinct haploid gametes.

• Variation Sources: Crossing over, independent assortment, random fertilization.

• Errors: Nondisjunction leads to aneuploidies (e.g., Down syndrome).

14. Mendel and the Gene Idea

Principles of Inheritance

• Law of Segregation: Alleles separate during gamete formation.

• Law of Independent Assortment: Genes on different chromosomes assort independently.

• Monohybrid Cross: 3:1 phenotype, 1:2:1 genotype ratio.

• Testcross: Cross with homozygous recessive to determine genotype.

• Extensions: Incomplete dominance, codominance, multiple alleles (e.g., ABO blood types), pleiotropy, epistasis, polygenic traits, environmental effects.

15. The Chromosomal Basis of Inheritance

Chromosomes and Human Genetics

• X-linked Inheritance: Males more likely to express recessive X-linked traits.

• Dosage Compensation: X inactivation (Barr bodies) in females.

• Chromosomal Disorders: Autosomal trisomies (e.g., trisomy 21), sex chromosome aneuploidies (Turner XO, Klinefelter XXY).

• Gene Linkage & Mapping: Recombination frequency (in map units) estimates gene distance.

16. The Molecular Basis of Inheritance

DNA Structure and Replication

• DNA Structure: Double helix, antiparallel strands, complementary base pairing (A–T, G–C).

• Replication: Semiconservative (each new DNA has one old and one new strand).

• Key Enzymes: Helicase (unwinds), primase (RNA primer), DNA polymerase III (synthesis), DNA polymerase I (primer removal), ligase (joins fragments), topoisomerase (relieves tension).

• Leading vs. Lagging Strand: Lagging strand synthesized in Okazaki fragments.

• Telomeres & Telomerase: Protect chromosome ends from degradation.

• DNA Repair: Mismatch repair, excision repair, photorepair.

17. Gene Expression: From Gene to Protein

Transcription and Translation

• Central Dogma: DNA → RNA → protein.

• Transcription: Initiation (promoter, RNA polymerase), elongation, termination.

• Eukaryotic mRNA Processing: 5’ cap, poly-A tail, splicing (removal of introns by spliceosome).

• Genetic Code: Triplet, universal, degenerate; start codon (AUG), stop codons (UAA, UAG, UGA).

• Translation: Initiation (small ribosomal subunit, tRNA-Met), elongation (A, P, E sites), termination (release factors).

• Mutations: Point (silent, missense, nonsense), frameshift, trinucleotide repeat expansions, structural variants.

18. Regulation of Gene Expression

Control Mechanisms in Eukaryotes

• Post-transcriptional: Alternative splicing, RNA editing, miRNA/siRNA (RISC complex).

• Translational & Post-translational: mRNA stability, protein degradation (ubiquitin-proteasome system).

19. Integrative Concepts and Exam Tips

Key Connections and Common Pitfalls

• Location Matters: Know where processes occur (e.g., transcription in nucleus, translation in cytoplasm, ETC in inner mitochondrial membrane).

• Order of Steps: Processes must occur in correct sequence (e.g., cell communication: reception → transduction → response).

• Inputs vs. Outputs: Distinguish what goes into and comes out of processes (e.g., photosynthesis vs. respiration).

• Structure vs. Function: Structure determines function (e.g., mitochondria produce ATP).

• Similar Terms: Do not confuse terms (e.g., transcription ≠ translation).

• Question Analysis: Read carefully for what is being asked; application questions may require deeper understanding.

20. Sample Table: Comparison of Mitosis and Meiosis

Feature	Mitosis	Meiosis
Number of Divisions	1	2
Number of Daughter Cells	2 (diploid)	4 (haploid)
Genetic Variation	Identical	Genetically unique
Role	Growth, repair	Gamete production

21. Additional Info

• Endosymbiosis Theory: Mitochondria and chloroplasts originated from engulfed prokaryotes.

• Negative Feedback: Maintains homeostasis (e.g., pH regulation).

• MAPK Pathway: Example of a kinase cascade in cell signaling.