Cumulative Biology Final Study Guide: Core Concepts and Integrative Review (Chapters 1–16, 26)

Introduction to Biology

Characteristics and Hierarchy of Life

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

• Biological Hierarchy: Organization proceeds from atoms → molecules → organelles → cells → tissues → organs → organ systems → organisms → populations → ecosystems → biosphere.

The Scientific Method

• Science: Relies on observation, hypothesis testing, and both deductive and inductive reasoning.

• Hypothesis-Driven Experiments: Involve controlled variables, testable predictions, and the rejection or refinement of hypotheses based on evidence.

• Theories: Broad, well-supported explanations integrating multiple hypotheses and observations.

Chemistry of Life

Atoms, Molecules, and Bonds

• Atoms: Composed of protons, neutrons, and electrons; isotopes differ in neutron number; ions are charged atoms.

• Chemical Bonds:

  • Ionic Bonds: Transfer of electrons.

  • Covalent Bonds: Sharing of electrons (polar: unequal sharing; nonpolar: equal sharing).

  • Hydrogen Bonds: Weak attractions between polar molecules.

  • Van der Waals Forces: Weak, transient interactions.

Water and pH

• Properties of Water: Cohesion, adhesion, high specific heat, high heat of vaporization, excellent solvent, hydrophobic interactions, and lower density as ice.

• pH: Acids donate H+; bases accept H+; buffers stabilize pH.

• pH Equation: $\mathrm{pH} = -\log_{10}[\mathrm{H}^+]$

Biomolecules

Carbohydrates

• Types: Monosaccharides, disaccharides, polysaccharides.

• Functions: Energy storage (starch in plants, glycogen in animals); structural (cellulose in plants, chitin in fungi and arthropods).

Lipids

• Types: Triglycerides (saturated and unsaturated), phospholipids (form bilayers), steroids, waxes.

• Functions: Energy storage, membrane structure, signaling molecules.

Proteins

• Structure: Composed of amino acids linked by peptide bonds; four levels of structure (primary, secondary, tertiary, quaternary).

• Denaturation: Loss of structure and function due to environmental changes.

• Chaperones: Assist in protein folding.

Nucleic Acids

• Types: DNA and RNA, composed of nucleotides joined by phosphodiester bonds.

• Functions: Genetic information storage (DNA), information transfer and protein synthesis (RNA), energy currency (ATP).

Cell Structure and Function

Prokaryotic vs. Eukaryotic Cells

• Prokaryotes: Lack nucleus and membrane-bound organelles; DNA is circular.

• Eukaryotes: Have nucleus, organelles, endomembrane system, mitochondria, and (in plants) chloroplasts (endosymbiotic origin), and cytoskeleton.

Cell Walls and Junctions

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

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

Membranes and Transport

Membrane Structure

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

Transport Mechanisms

• Passive Transport: Diffusion, osmosis, facilitated diffusion via channels/carriers.

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

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

• Tonicity: Hypertonic, hypotonic, isotonic solutions affect cell volume.

Energy and Metabolism

Thermodynamics and Free Energy

• First Law: Energy cannot be created or destroyed.

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

• Free Energy Equation: $\Delta G = \Delta H - T\Delta S$

• Spontaneity: Negative $\Delta G$ = spontaneous; positive $\Delta G$ = requires energy input.

Enzymes and ATP

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

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

Cellular Respiration

Stages of Aerobic Respiration

1. Glycolysis: Occurs in cytosol; 1 glucose → 2 pyruvate, 2 ATP, 2 NADH.

2. Pyruvate Oxidation: In mitochondrial matrix; pyruvate → acetyl-CoA, NADH, CO2.

3. Citric Acid Cycle: Acetyl-CoA → 3 NADH, 1 FADH2, 1 ATP, CO2 per turn.

4. Electron Transport Chain (ETC) & 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 to control pathway flux.

Photosynthesis

Overview and Pathways

• 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: Occur in thylakoid membranes; involve PSII and PSI, water splitting (produces O2), ATP, and NADPH.

• Calvin Cycle: Occurs in stroma; carbon fixation (Rubisco), reduction (G3P), regeneration of RuBP.

• Photorespiration: Rubisco uses O2 instead of CO2, wasting carbon; C4 (spatial separation) and CAM (temporal separation) plants minimize this.

Cell Communication

Types of Signals and Receptors

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

• Receptors: Intracellular (e.g., steroid hormones) and cell-surface (ion channels, enzyme-linked receptors like RTKs, G protein-coupled receptors [GPCRs]).

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

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

• GPCRs: Activate GTP-binding proteins, which regulate effector enzymes.

Cell Cycle and Mitosis

Phases and Regulation

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

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

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

Meiosis and Sexual Reproduction

Process and 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.

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

• Errors: Nondisjunction leads to aneuploidies (abnormal chromosome numbers).

Mendelian Genetics

Principles and Extensions

• Law of Segregation: Alleles separate during gamete formation.

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

• Monohybrid Cross: 3:1 phenotype ratio, 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.

Chromosomes and Human Genetics

Inheritance Patterns and Disorders

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

• Dosage Compensation: X inactivation forms Barr bodies in females.

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

• Gene Linkage and Mapping: Recombination frequency used to estimate map units (distance between genes).

DNA Structure and Replication

Structure and Enzymes

• 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; demonstrated by Meselson-Stahl experiment).

• 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 Strands: Lagging strand synthesized in Okazaki fragments.

• Telomeres and Telomerase: Protect chromosome ends from degradation.

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

Gene Expression

Central Dogma and Processes

• 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 mutations (silent, missense, nonsense), frameshift, trinucleotide repeat expansions, structural variants.

Control of Gene Expression

Regulation in Eukaryotes

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

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

Integrative Concepts and Exam Strategies

Location, Sequence, and Inputs/Outputs

• Location Matters: Know where processes occur (e.g., light reactions in thylakoid, Calvin cycle in stroma, 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; central dogma: DNA → RNA → protein).

• Inputs vs. Outputs: Distinguish what goes into and comes out of each process (e.g., photosynthesis light reactions produce ATP/NADPH; Calvin cycle uses them to make sugar).

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

• Similar Terms: Do not confuse related but distinct terms (e.g., transcription vs. translation, mitosis vs. meiosis).

Exam Tips

• Read questions carefully for qualifiers like “best describes,” “most likely,” etc.

• Focus on application, not just definitions.

• Review areas where you mix up locations, sequences, or similar terms.

• Be able to explain where a process happens, what goes in and out, and what changes.

Summary Table: Key Processes and Locations

Process	Location	Inputs	Outputs
Glycolysis	Cytosol	Glucose, 2 ATP, 2 NAD+	2 Pyruvate, 4 ATP (net 2), 2 NADH
Citric Acid Cycle	Mitochondrial matrix	Acetyl-CoA, NAD+, FAD	CO2, NADH, FADH2, ATP
Electron Transport Chain	Inner mitochondrial membrane	NADH, FADH2, O2	ATP, H2O
Light Reactions (Photosynthesis)	Thylakoid membrane	Light, H2O, NADP+, ADP	O2, ATP, NADPH
Calvin Cycle	Stroma (chloroplast)	CO2, ATP, NADPH	G3P (sugar), ADP, NADP+
Transcription	Nucleus (eukaryotes)	DNA, RNA nucleotides	Pre-mRNA
Translation	Cytoplasm (ribosomes)	mRNA, tRNA, amino acids	Polypeptide (protein)