DNA replication is the process by which a cell makes an exact copy of its DNA before dividing. This study note covers the semiconservative model (Meselson-Stahl), the replication fork structure, the major enzymes (helicase, primase, DNA polymerase, ligase, topoisomerase), the leading vs lagging strand distinction with Okazaki fragments, proofreading and mismatch repair, and the telomere end-replication problem.
Biology
The immune system is the body’s defense against pathogens and transformed cells. This study note covers the two branches (innate vs adaptive), the cells involved (phagocytes, NK cells, T cells, B cells), antibodies and their five classes, immunological memory and vaccination, self-tolerance mechanisms, and the failure modes (immunodeficiency, allergies, autoimmunity, sepsis, cancer immune evasion).
The cell cycle is the ordered sequence a eukaryotic cell goes through from its birth to its division. This study note covers the four phases (G1, S, G2, M), their relative durations in a typical 24-hour human cycle, the three major checkpoints (G1/S restriction point, G2/M, spindle assembly), the cyclin/CDK regulatory engine, the G0 resting state, and how cell-cycle dysregulation is the central problem in cancer.
Osmosis is the passive movement of water across a semipermeable membrane from low solute to high solute concentration. This study note covers the precise definition, why water moves (kinetic theory), tonicity vocabulary (hypotonic, hypertonic, isotonic), osmotic pressure and the van’t Hoff equation, biological roles (cell volume regulation, plant turgor, kidney function, IV fluids), and the difference between osmosis and diffusion.
Meiosis halves chromosome-set number through 2 nuclear divisions after 1 round of DNA replication. Study homologues, sister chromatids, genetic variation, animal gamete formation and plant spores with diagrams and practice.
The standard glycolytic pathway splits glucose into 2 pyruvate in the cytosol, giving 2 net ATP and 2 NADH. Learn its investment and payoff stages, carrier regeneration and the distinction between fermentation and respiration.
The Krebs cycle (citric acid cycle, TCA cycle) is the second stage of aerobic cellular respiration. This study note covers where the cycle sits in the bigger picture of respiration, the per-acetyl-CoA inputs and outputs (3 NADH, 1 FADH2, 1 GTP, 2 CO2), the eight enzymatic steps, why the cycle’s intermediates also feed biosynthesis, and how it is regulated by energy demand.
Natural selection is the process by which heritable traits affecting survival and reproduction become more or less common over generations. This study note covers the four conditions for natural selection, the peppered moth example, directional vs stabilizing vs disruptive selection, sexual selection, common misconceptions, and how natural selection fits into the broader modern evolutionary synthesis.
A Punnett square is a 2D grid that predicts the genotype and phenotype ratios of offspring from a known parental cross. This study note covers vocabulary (gene, allele, genotype, phenotype, dominant, recessive), how to build the basic 2×2 cross, the famous 3:1 phenotypic ratio, common cross types, the 4×4 dihybrid square and 9:3:3:1 ratio, and the limitations where the Punnett square breaks down.
The human nervous system is the body’s electrical and chemical communication network — 86 billion neurons connecting through 150 trillion synapses. This study note covers the CNS and PNS divisions, somatic vs autonomic, sympathetic vs parasympathetic, the neuron, action potentials, synapses and neurotransmitters, and glial cells.
Ribosomes read mRNA and build proteins. Compare bacterial 70S, eukaryotic cytosolic 80S and mammalian mitochondrial 55S particles, then study translation, polysomes and antibiotic targets.
Homeostasis is the maintenance of stable internal conditions across changing external environments. This study note covers the four components of a homeostatic loop (setpoint, sensor, control center, effector), negative vs positive feedback, examples across temperature, glucose, pH, blood pressure, and what happens when homeostasis fails.