Cell Biology
The molecular machines inside every cell, in motion: pumps, motors, ribosomes, and the signals that make them move.
19 units · 132 topics · 646 questions
Why carbon builds everything, why water behaves like nothing else, and how four families of polymers get assembled from small repeating parts.
Carbon's Bonding Versatility and Functional Groups · Water, Hydrogen Bonding, and Life's Solvent · pH, Buffers, and Biological Systems · Carbohydrates: From Monosaccharides to Polysaccharides · +3 more
How a floppy chain of amino acids becomes an exact three-dimensional machine, what happens when folding fails, and how biologists actually see the result.
Primary and Secondary Protein Structure · Tertiary and Quaternary Protein Structure · Molecular Chaperones and Assisted Folding · Protein Misfolding, Aggregation, and Prion Disease · +2 more
How a protein speeds up a reaction by a million-fold without being consumed, and the math that turns a saturating rate curve into two numbers.
Activation Energy and Enzyme Catalysis · The Active Site, Binding, and Specificity · Michaelis-Menten Kinetics · Finding Km and Vmax from a Lineweaver-Burk Plot · +3 more
The plasma membrane as a two-dimensional fluid: how it assembles itself, why its two faces differ, and what actually controls how loose or stiff it is.
The Fluid Mosaic Model · The Hydrophobic Effect and Bilayer Self-Assembly · Membrane Fluidity and Fatty Acid Saturation · Cholesterol's Role in Membrane Fluidity · +3 more
How a cell decides what crosses its membrane and how, and how those transport decisions add up to a voltage sitting across every living cell.
Simple Diffusion Across a Lipid Bilayer · Osmosis and Tonicity · Facilitated Diffusion Through Channels and Carriers · Aquaporins and Water Channel Specificity · +4 more
How a cell addresses, folds, modifies, and ships every protein it makes to the exact compartment it belongs in, one vesicle at a time.
Signal Sequences and Protein Sorting Decisions · Co-translational Translocation into the Rough ER · Protein Folding and Quality Control in the ER · The Golgi Apparatus and Sequential Protein Modification · +4 more
Three filament systems and the motor proteins that walk, pull, and crawl along them to move cargo, divide a cell, and drive a whole cell across a surface.
Actin Filament Structure and Treadmilling · Actin-Binding Proteins and the Cell Cortex · Microtubule Structure and Dynamic Instability · The Centrosome and Microtubule Organization · +4 more
What holds a tissue together from the outside in: the fibers cells build around themselves, and the junctions that seal, anchor, and connect them to each other.
Collagen Structure and Assembly · Proteoglycans and the Ground Substance · Integrins and Cell-Matrix Adhesion · Tight Junctions and the Paracellular Barrier · +2 more
ATP as the cell's spendable energy currency, and the ten-step pathway that pulls the first small yield of it out of a glucose molecule.
Free Energy, ATP, and the Energy Currency of the Cell · Coupled Reactions and ATP Hydrolysis · Glycolysis: Substrate-Level Phosphorylation Step by Step · Regulation of Glycolysis by Phosphofructokinase · +2 more
Where most of a glucose molecule's energy actually gets extracted: a spinning loop of oxidations feeding a proton gradient that spins a molecular turbine.
Pyruvate Oxidation and the Citric Acid Cycle · Electron Carriers: NADH and FADH2 · The Electron Transport Chain · Chemiosmosis and the Proton Motive Force · +2 more
How a chloroplast captures light, turns it into a proton gradient, and spends that gradient's ATP and NADPH pulling carbon out of the air.
Chloroplast Structure and the Thylakoid Membrane · Light Absorption and the Light Reactions · Chemiosmosis in the Chloroplast · The Calvin Cycle and Carbon Fixation · +2 more
The checkpoints that decide when a cell is allowed to divide, the choreography that splits its chromosomes, and the extra round that halves them again for sex.
The Phases of the Cell Cycle · Cyclins, CDKs, and Checkpoint Control · Mitosis: Prophase Through Telophase · The Mitotic Spindle and Chromosome Segregation · +4 more
The cell's own self-destruct program, and what happens to a lineage of cells when that program and the checkpoints that call it both fail.
Apoptosis and the Caspase Cascade · Intrinsic and Extrinsic Apoptotic Pathways · Cancer as a Disease of Cell Cycle Control · Oncogenes and Tumor Suppressor Genes · +2 more
The double helix as an information-carrying molecule: how it's copied with almost no errors, and what fixes the errors that slip through anyway.
The Double Helix and Base Pairing · Semiconservative Replication · The Replication Fork: Helicase, Primase, and Polymerase · Leading and Lagging Strands and Okazaki Fragments · +3 more
From a promoter recruiting RNA polymerase to a ribosome ratcheting out a finished protein, with the RNA editing steps in between.
RNA Polymerase and the Promoter · Transcription: Initiation, Elongation, and Termination · Pre-mRNA Splicing and the Spliceosome · Alternative Splicing and Protein Diversity · +4 more
How a cell decides which genes to switch on, from a bacterium sensing one sugar to the chromatin marks that lock in a whole expression pattern across divisions.
The Lac Operon and Prokaryotic Gene Regulation · Eukaryotic Transcription Factors and Enhancers · Chromatin Structure and the Nucleosome · Histone Modification and the Histone Code · +2 more
How a molecule that never enters a cell still changes its behavior: receptors, second messengers, kinase cascades, and the amplification built into every step.
Signal Transduction from Ligand to Response · G-Protein-Coupled Receptors and Heterotrimeric G Proteins · Second Messengers: cAMP and Protein Kinase A · Calcium and IP3 Signaling · +3 more
How one fertilized cell commits to hundreds of fates, why some fates can be reversed, and how a whole animal can be rebuilt from a single adult nucleus.
Cell Differentiation and the Stability of Cell Fate · Embryonic Stem Cells and Pluripotency · Induced Pluripotent Stem Cells · Morphogen Gradients and Positional Information · +2 more
The tools that let anyone see, sort, copy, cut, or read what a cell is made of and doing — from a microscope's resolution limit to editing a genome on purpose.
Light and Fluorescence Microscopy · Electron Microscopy: TEM and SEM · Cell Fractionation by Differential Centrifugation · Gel Electrophoresis of Proteins and Nucleic Acids · +5 more