🔬 Cell Biology: One Night Revision & Cram Sheet
Explain how the structure of a cell produces its functions: boundary, compartments, energy conversion, protein sorting, shape, division, communication, and death.
🌟 Core Axioms & High-Yield Golden Rules
9 Core PrinciplesNon-negotiable foundational truths frequently tested in direct conceptual and numerical exam questions. Click checkbox to mark as mastered.
Fluid Mosaic Model: Phospholipid bilayer is fluid; cholesterol buffers membrane fluidity (prevents extremes of fluidity at high temperatures and stiffness at low temperatures).
💡 Cholesterol = Fluidity BufferPhosphatidylserine is normally restricted to the inner leaflet by flippases; externalization to the outer leaflet serves as an 'eat-me' signal for phagocytes in apoptosis.
💡 PS outside = Apoptosis signalNa+/K+ ATPase pumps 3 Na+ out of the cell and 2 K+ into the cell per ATP hydrolyzed; it is electrogenic and inhibited by cardiac glycosides (ouabain, digitalis).
💡 3 Na+ OUT, 2 K+ IN (NOKI)Nuclear import requires NLS (nuclear localization signal), Importin alpha/beta, and Ran-GTP in the nucleus; Ran-GAP in cytoplasm drives GTP hydrolysis.
💡 Ran-GTP high in nucleus, low in cytoplasmVesicle coat proteins: COPII mediates anterograde transport (ER to cis-Golgi); COPI mediates retrograde transport (Golgi to ER); Clathrin mediates endocytosis and trans-Golgi to lysosome.
💡 COPII = Forward | COPI = BackwardCytoskeleton polarities: Microtubules polymerize at (+) end toward cell periphery; Kinesin moves anterograde toward (+) end; Dynein moves retrograde toward (-) end (centrosome).
💡 Kinesin kicks out (+), Dynein drags in (-)Cilia and flagella axoneme exhibits 9+2 microtubule doublet arrangement; basal body and centrioles exhibit 9+0 triplet arrangement.
💡 Axoneme = 9+2 | Centriole = 9+0Cell cycle engine: Cyclins bind and activate CDKs; Cyclin B-CDK1 (MPF) triggers entry into mitosis; p53 arrests cell at G1 checkpoint by transcribing p21 (CDK inhibitor).
💡 p53 -> p21 -> CDK arrestedExtrinsic apoptosis is triggered by FasL/TNF binding death receptors -> Caspase-8; Intrinsic apoptosis is triggered by mitochondrial cytochrome c release -> Apaf-1 apoptosome -> Caspase-9.
💡 Extrinsic = 8 | Intrinsic = 9 | Executioner = 3, 7📚 Chapter-by-Chapter Rapid Cram Breakdown
13 ModulesHigh-density review of every curriculum chapter. Click any chapter title to view full in-depth lecture notes.
The cell →
- Master Cell theory: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master prokaryotes: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master eukaryotes: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master model organisms: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
How cells are studied →
- Master Light microscopy: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master electron microscopy: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master centrifugation: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Bilayer and fluid mosaic: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master diffusion and proteins: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master pumps and potential: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Nucleus: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master ER: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Golgi: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master lysosomes: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master peroxisomes: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Bacterial and plant walls: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master ECM: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master cell–cell and cell–matrix junctions: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Actin: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master microtubules: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master intermediate filaments: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master motors: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master cilia: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Signal hypothesis: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master ER translocation: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master folding and quality control: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Golgi processing: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master coats: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master fusion: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master secretion: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master endocytosis: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Nuclear pores and Ran: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master TOM/TIM: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master TOC/TIC: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master PTS receptors: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Interphase: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master mitotic stages: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master meiosis I and II: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Cyclins and CDKs: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master checkpoints: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master licensing of replication: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
Cell signaling →
- Master Signal range: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master GPCRs: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master RTKs: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master second messengers: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master steroid receptors: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Apoptosis: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master necrosis: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master stem cells: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master the transformed cell: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master flow cytometry: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
⚖️ Must-Know Comparison & Distinction Tables
2 TablesSide-by-side matrices comparing commonly confused biological mechanisms, kinetic types, and pathways.
Vesicle Trafficking Coat Proteins & Functions
| Coat Type | Transport Direction | GTPase Involved | Cargo / Markers |
|---|---|---|---|
| COPII | Anterograde (Rough ER -> cis-Golgi) | Sar1 GTPase | Newly synthesized proteins, secretory cargo |
| COPI | Retrograde (cis-Golgi -> Rough ER) | Arf1 GTPase | Escaped ER resident proteins bearing KDEL signal |
| Clathrin | Trans-Golgi -> Lysosomes / Plasma Membrane -> Endosomes | Dynamin (vesicle fission) | Mannose-6-phosphate receptor, LDL receptor |
Cytoskeletal Filament Systems
| Filament Type | Subunit Protein | Diameter | Polarity & Motor Proteins |
|---|---|---|---|
| Microfilaments | G-actin / F-actin | 7 nm | Polar (+ and - ends); Myosin motors |
| Intermediate Filaments | Keratins, Vimentin, Lamin, Neurofilaments | 10 nm | Non-polar; NO motor proteins (structural support) |
| Microtubules | alpha- and beta-tubulin heterodimers | 25 nm | Polar (+ and - ends); Kinesin (+) and Dynein (-) motors |
⚠️ Examiner Traps & Common Student Mistakes
2 PitfallsClassic trap questions designed by examiners to catch uncritical students. Don't lose easy marks here!
Centriole vs Axoneme Microtubule Architecture
Saying all microtubule structures are 9+2 doublets.
The axoneme of mobile cilia/flagella has a 9+2 doublet pattern. The basal body and centriole have a 9+0 triplet pattern and lack central singlets.
Motor Protein Direction Confusion
Thinking dynein moves outward to the membrane.
Dynein moves toward the MINUS end (retrograde, toward MTOC/centrosome). Kinesin moves toward the PLUS end (anterograde, toward plasma membrane).
📐 Key Formulas & Numerical Constants
2 FormulasNernst Equation for Single Ion Equilibrium
E_ion = (61.5 / z) * log10([ion]_out / [ion]_in) mVCalculates electrical potential required to balance concentration gradient of an ion at 37°C.
Goldman-Hodgkin-Katz (GHK) Equation
Vm = 61.5 * log10((P_K[K+]o + P_Na[Na+]o + P_Cl[Cl-]i) / (P_K[K+]i + P_Na[Na+]i + P_Cl[Cl-]o))Calculates true resting membrane potential considering multiple permeable ions and their permeability ratios.
🏛️ Landmark Scientists & Nobel Discoveries
6 PioneersFrequently tested in historical milestone and match-the-following exam questions.
Sir Hans Adolf Krebs
🏅 Nobel Prize in Physiology or Medicine (1953) for his discovery of the citric acid cycleMajor landmark discoveries
Peter Dennis Mitchell
🏅 Nobel Prize in Chemistry (1978) for his contribution to the understanding of biological energy transfer through the chemiosmotic theoryMajor landmark discoveries
Robert Hooke
🏅 Pre-dated the Nobel Prize; England's Leonardo da Vinci; co-founder of microscopy and cytologyMajor landmark discoveries
George Emil Palade
🏅 Nobel Prize in Physiology or Medicine (1974) for discoveries concerning the structural and functional organization of the cellMajor landmark discoveries
Christian René de Duve
🏅 Nobel Prize in Physiology or Medicine (1974) for discoveries concerning the structural and functional organization of the cellMajor landmark discoveries
Lynn Margulis
🏅 National Medal of Science (1999); Member of the National Academy of Sciences (1983)Major landmark discoveries
🎯 Rapid-Fire Active Recall Checklist
5 QuestionsTest your memory before stepping into the exam hall. Try to answer mentally, then tap "Reveal Answer" to verify!