BIG IDEA I: Structure Relates to Function

Biological Hierarchy

Biological systems are organized into a hierarchy of complexity, from atoms to ecosystems. Understanding these levels helps explain how structure and function are interrelated in living organisms.

• Levels of Biological Organization: Atoms → Molecules → Organelles → Cells → Tissues → Organs → Organ Systems → Organisms → Populations → Communities → Ecosystems → Biosphere.

• Emergent Properties: New properties arise at each level due to interactions among components (e.g., consciousness emerges from neural networks).

• Experimental Design: Scientists use controlled experiments, hypothesis testing, and data analysis to develop theories and laws.

• Example: The heart is made of muscle cells (tissue) that together pump blood (organ function).

Chemistry for Biology

The structure and properties of chemicals determine the behavior and functions of molecules in organisms.

• Stable Biological Molecules: Constructed from C, H, O, N, S, P atoms via covalent bonds. Polar covalent bonds (unequal sharing) vs. nonpolar covalent bonds (equal sharing).

• Covalent vs. Non-covalent Bonds: Covalent bonds involve shared electrons; non-covalent interactions include ionic bonds, hydrogen bonds, dipole interactions, and hydrophobic/hydrophilic effects.

• Hydrogen Bonding: Polar regions (e.g., water) form hydrogen bonds; nonpolar molecules (e.g., oils) do not.

• Water Properties: High cohesion, adhesion, heat capacity, solvent abilities due to hydrogen bonding. Supports life by facilitating reactions and temperature regulation.

• pH and Ion Concentration: ; low pH = acidic, high pH = basic. Buffers maintain stable pH in biological systems.

• Example: Water's high heat capacity helps organisms maintain temperature.

Biological Molecules

Cells are composed of biological molecules with specific chemical properties.

• Carbon Compounds: Diverse due to carbon's ability to form four bonds; functional groups (e.g., hydroxyl, carboxyl) determine polarity and charge.

• Monomers and Polymers: Four groups: carbohydrates (monosaccharides), lipids (fatty acids/glycerol), proteins (amino acids), nucleic acids (nucleotides).

• Condensation and Hydrolysis: Polymers form by condensation (dehydration synthesis), break down by hydrolysis.

• Carbohydrate Polymers: Glycogen (animal storage), starch (plant storage), cellulose (plant structure).

• Lipids: Triglycerides, phospholipids, steroids; saturated (no double bonds) vs. unsaturated (double bonds) fatty acids affect fluidity.

• Protein Structure: Four levels: primary (sequence), secondary (alpha helix/beta sheet), tertiary (3D folding), quaternary (multiple polypeptides). Bonds: peptide, hydrogen, ionic, hydrophobic interactions.

• DNA vs. RNA: DNA: double helix, deoxyribose, A-T, G-C; RNA: single-stranded, ribose, A-U, G-C. Purines (A, G), pyrimidines (C, T, U).

• Example: Cellulose's structure makes it rigid and insoluble, ideal for plant cell walls.

Origin of Life

The first living cells originated by chemical evolution on pre-biotic Earth.

• Hypotheses: Miller-Urey experiment showed amino acids could form under early Earth conditions.

• First Hereditary Molecule: RNA is a candidate due to its ability to store information and catalyze reactions.

• Evidence for Common Ancestor: Universal genetic code, conserved metabolic pathways.

• Endosymbiosis: Mitochondria and chloroplasts originated from engulfed prokaryotes.

• Example: Mitochondria have their own DNA, supporting endosymbiotic theory.

Cell Structure

Cell structure has evolved to perform essential functions.

• Cell Biology Methods: Microscopy, cell fractionation, molecular markers.

• Three Domains: Bacteria, Archaea, Eukarya differ in membrane, cell wall, genome structure.

• Eukaryotic Organelles: Nucleus (DNA storage), mitochondria (energy), ER (protein/lipid synthesis), Golgi (processing), lysosomes (digestion).

• Organelle Defects: Mitochondrial diseases, lysosomal storage disorders.

• Specialized Cells: Macrophages have abundant lysosomes; lymphocytes have extensive ER.

• Protein Pathway: Synthesis in ribosomes → ER → Golgi → membrane or secretion.

• Plant vs. Animal Cells: Plant cells have cell walls, chloroplasts, plasmodesmata; animal cells have centrioles, tight junctions.

• Example: Red blood cells lack nuclei to maximize space for hemoglobin.

Biological Membrane

Cell membranes are selectively permeable barriers.

• Membrane Components: Phospholipids (bilayer), cholesterol (fluidity), proteins (transport, signaling), oligosaccharides (recognition).

• Fluidity: Influenced by lipid composition and temperature.

• Transport Modes: Simple diffusion (no energy), facilitated diffusion (channels), active transport (ATP), coupled transport, bulk transport (endocytosis/exocytosis).

• Electrochemical Gradients: Ion transport generates gradients used in nerve impulses.

• Osmosis: Water moves across membranes via aquaporins or bilayer; direction depends on solute concentration.

• Example: Sodium-potassium pump maintains cell potential.

Cell Communication

Cells communicate and convert environmental signals to integrated responses.

• Signal Molecules: Lipid-soluble (e.g., steroids) vs. water-soluble (e.g., peptides); receptors can be intracellular or membrane-bound.

• Signal Transduction Pathways: Components include receptors, signals, enzymes, second messengers (e.g., cAMP).

• Amplification: Binding a few signal molecules can trigger phosphorylation cascades and gene expression changes.

• Regulation: Feedback mechanisms, receptor desensitization.

• Example: Epinephrine triggers a cascade leading to glucose release.

BIG IDEA II: Energy is Stored, Used, and Transformed in Living Systems

Metabolism

Energy transfer and transformation are critical to all aspects of biology.

• Free Energy: Spontaneous reactions (), non-spontaneous (); governed by thermodynamics.

• Endergonic vs. Exergonic: Endergonic absorbs energy; exergonic releases energy.

• ATP: Hydrolysis releases energy for cellular work; energy coupling links exergonic and endergonic reactions.

• Enzymes: Lower activation energy, increase reaction rate; affected by pH, temperature, substrate concentration.

• Regulation: Activators, inhibitors, allosteric regulation, feedback inhibition.

• Example: ATP powers muscle contraction.

Respiration

Organic molecules are broken down in cellular respiration to make ATP.

• Overview: Cellular respiration involves redox reactions and energy coupling.

• Stages: Glycolysis, acetyl CoA formation, citric acid cycle, oxidative phosphorylation; linked by electron carriers (NADH, FADH2).

• Fuel Molecules: Carbohydrates, lipids, proteins can all be used to produce ATP.

• Phosphorylation: Oxidative (ETC, ATP synthase) vs. substrate-level (direct transfer).

• Sites: Prokaryotes (cytoplasm, membrane), eukaryotes (mitochondria).

• Regulation: Feedback mechanisms, substrate availability.

• Fermentation vs. Respiration: Fermentation (alcohol/lactate) occurs without oxygen; respiration (aerobic/anaerobic) with/without oxygen.

• Example: Yeast ferments glucose to ethanol in anaerobic conditions.

Photosynthesis

Light energy is harnessed into chemical bond energy in photosynthesis.

• Leaf Anatomy & Chloroplasts: Structure enables efficient light capture; photosystems harvest energy.

• Light Reactions & Calvin Cycle: Light reactions produce ATP/NADPH; Calvin cycle fixes CO2 into carbohydrates.

• RuBisCO: Enzyme can limit Calvin cycle rate under certain conditions.

• C4 and CAM Pathways: Adaptations to improve efficiency in hot/dry environments.

• Mitochondria vs. Chloroplasts: Both make ATP; mitochondria via oxidative phosphorylation, chloroplasts via photophosphorylation.

• Global Carbon Cycle: Photosynthesis fixes CO2; respiration releases CO2.

• Example: CAM plants open stomata at night to conserve water.

BIG IDEA III: Genetic Information is Transmitted and Expressed

Cell Cycle

Mitotic cell division allows for growth, development, repair, and asexual reproduction.

• Phases: G1, S (DNA synthesis), G2, M (mitosis), cytokinesis.

• Processes: Cell signaling, DNA replication, mitosis, cytokinesis produce identical daughter cells.

• Control Systems: Checkpoints regulate progression; mutations can lead to cancer.

• Example: Loss of checkpoint control in p53 leads to tumor formation.

Meiosis

Genetic information is transmitted through mitosis, meiosis, and fertilization.

• Mitosis vs. Meiosis: Mitosis produces identical somatic cells; meiosis produces genetically diverse gametes.

• Genome: Diploid cells have maternal and paternal chromosomes.

• Chromosome Number: Changes during meiosis and fertilization (haploid → diploid).

• Genetic Variation: Independent assortment and crossing over generate diversity.

• Example: Tracking alleles through meiosis explains inheritance patterns.

Mendelian Inheritance

Mendel’s laws explain many patterns of trait inheritance.

• Genotype vs. Phenotype: Genotype (genetic makeup), phenotype (observable traits); dominant/recessive alleles.

• Law of Segregation: Alleles separate during gamete formation.

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

• Punnett Squares: Used to predict offspring genotypes/phenotypes.

• Molecular Basis: Dominant traits often gain-of-function; recessive traits often loss-of-function.

• Example: Cystic fibrosis is caused by a homozygous recessive mutation.

DNA Structure & Replication

DNA is the molecule of heredity in all organisms.

• Double Helix: Sugar-phosphate backbone, 5’ and 3’ ends, complementary base pairing.

• Evidence: Experiments (e.g., Hershey-Chase) showed DNA is hereditary material.

• Semi-conservative Replication: Each new DNA has one old and one new strand.

• Enzymes: DNA polymerase (synthesis), DNA ligase (joining fragments).

• Leading vs. Lagging Strands: Anti-parallel arrangement causes Okazaki fragments on lagging strand.

• Example: Meselson-Stahl experiment demonstrated semi-conservative replication.

Transcription & Translation

Genetic information flows from DNA to RNA to protein.

• Gene Structure: Includes regulatory regions (promoter, enhancer).

• Transcription: RNA polymerase binds promoter, synthesizes RNA from template strand.

• RNA Processing: Introns removed, exons spliced; alternate splicing produces multiple proteins.

• Translation: Ribosome reads mRNA, tRNA brings amino acids; universal codon table used.

• Mutations: Can alter protein structure/function; types include point, frameshift, nonsense.

• Locations: Prokaryotes: transcription/translation in cytoplasm; eukaryotes: transcription in nucleus, translation in cytoplasm.

• Example: Sickle cell anemia caused by a single nucleotide mutation.

Gene Regulation

Cells regulate gene expression at multiple points.

• Prokaryotic Regulation: Operons (e.g., lac operon) control transcription initiation.

• Inducible vs. Repressible Operons: Inducible (activated by substrate), repressible (inactivated by product).

• Eukaryotic Regulation: Chromatin packing, regulatory DNA sequences, proteins.

• Differential Expression: Regulation at transcriptional, post-transcriptional, translational, post-translational levels.

• Cell Specialization: Tissue-specific gene expression determines cell function.

• Example: Hemoglobin genes expressed only in red blood cells.

Recombinant DNA

Scientists use gene structure and regulation knowledge to express modified genes.

• Tools: Restriction enzymes, plasmid/viral vectors, host cells.

• Techniques: Gel electrophoresis, sequencing, PCR.

• Cloning Flowchart: Insert gene into plasmid → transform bacteria → express protein.

• Applications: Recombinant insulin production, gene therapy.

• Example: Recombinant DNA technology used to treat diabetes.

Core Competencies for Biology Students

• Process of Science: Practice observation, hypothesis generation, experiment design, data manipulation.

• Quantitative Reasoning: Manipulate numerical data, use mathematical/statistical methods.

• Critical Thinking: Apply concepts to novel situations, evaluate sources.

• Independent Learning: Set goals, self-assess progress.

• Exchange of Ideas: Collaborate, discuss, explore creative solutions.

• Biology and Society: Apply concepts to daily life and societal issues.