Explore the archive
Ask a biology question, or look up a molecule, gene, pathway, or identifier.
Popular Starting Points
104 recordsGlycolysis · Glycolysis (human)
The ten-step cytosolic pathway that splits one glucose into two pyruvate, with a net gain of 2 ATP and 2 NADH.
Cellular Respiration · Cellular respiration
How cells transfer energy from fuel molecules into ATP, often using oxygen in the final electron-accepting step.
Citric Acid cycle · Citric acid cycle in human metabolism
The citric acid cycle oxidizes the acetyl group of acetyl-CoA to two carbon dioxide molecules while regenerating oxaloacetate. Each turn yields three NADH, one FADH2, and one GTP (or ATP), which feed biosynthesis and oxidative phosphorylation.
Photosynthesis
The capture of light energy and transfer of carbon from carbon dioxide into organic molecules by plants, algae, and some bacteria.
DNA Replication · DNA replication
How a cell copies its DNA before division.
Translation
How ribosomes read mRNA and build a protein from amino acids.
Acquired Drug resistance · Acquired drug resistance
A reduction in drug response that develops as cells or tumors adapt under treatment pressure.
Action Potential · Action potential
A rapid, regenerative change in membrane voltage that carries signals along excitable cells such as neurons.
Active Membrane Transport
Transport that moves substances against a gradient by coupling movement to an energy source.
Adaptive Immune Response
Antigen-specific B- and T-cell responses that can form immunological memory.
Adipose Tissue metabolism · Adipose tissue metabolism
Adipose tissue stores triglycerides after feeding and releases fatty acids during energy demand.
Allosteric Regulation · Allosteric regulation
Control of a protein's activity when a molecule binds at a site other than its main working site.
Antigen Presentation · Antigen presentation
Display of peptide fragments on major histocompatibility complex molecules for recognition by T cells.
Antimicrobial Resistance · Antimicrobial resistance
A heritable or acquired microbial property that reduces susceptibility to an antimicrobial agent.
Apoptosis · Programmed cell death
A regulated form of cell death that helps remove cells during development and in response to certain stresses.
Apoptosis Signaling · Apoptosis signaling
The regulated pathways cells use to initiate and execute programmed cell death.
Bacterial Conjugation · Bacterial conjugation
Contact-associated transfer of DNA between bacterial cells, often involving a conjugative plasmid.
Bacterial Transduction · Bacterial transduction
Transfer of bacterial DNA between cells by a bacteriophage.
Bacterial Transformation · Bacterial transformation
Uptake and incorporation of extracellular DNA by a competent bacterial cell.
Brain Metabolism · Brain metabolism
The brain requires a continuous energy supply and can adapt fuel use during prolonged fasting.
Branched-chain Amino acid catabolism · Branched-chain amino acid catabolism in human metabolism
Leucine, isoleucine, and valine share transamination and oxidative decarboxylation steps, then diverge. Leucine is ketogenic; isoleucine is both ketogenic and glucogenic; valine is glucogenic. Their carbon enters metabolism as acetyl-CoA, acetoacetate, or succinyl-CoA.
Calvin Cycle · Calvin cycle
A chloroplast-stroma cycle that uses ATP and NADPH to incorporate carbon dioxide into triose phosphate and regenerate its carbon acceptor.
Carbohydrate Biosynthesis · Carbohydrate biosynthesis
The conversion of triose phosphates from carbon fixation into sucrose, starch, and other carbohydrates.
Carbon Cycle · Carbon cycle
The movement of carbon among atmospheric, aquatic, geological, and living reservoirs through biological and physical processes.
Carbon Fixation · Carbon fixation
Incorporation of inorganic carbon, such as CO₂, into organic molecules by an organism.
Cell Cycle · Cell cycle
The ordered stages a cell follows as it grows and divides.
Cellular Metabolism · Cellular metabolism
The connected reactions cells use to obtain energy and build the molecules they need.
Chemiosmosis
The use of an ion gradient across a membrane to power a cellular process such as ATP synthesis.
Cholesterol Biosynthesis · Cholesterol biosynthesis in human metabolism
Cells build cholesterol from acetyl-CoA through the mevalonate pathway. Acetyl units form HMG-CoA, HMG-CoA reductase makes mevalonate, and activated isoprenes assemble into squalene, lanosterol, and finally cholesterol.
Cholesterol Homeostasis · Cholesterol homeostasis
The balance of cholesterol synthesis, uptake, transport, and removal across tissues.
Covalent KRAS inhibition
A drug strategy that forms a covalent bond with a mutant cysteine in KRAS G12C to inhibit selected KRAS states.
Crossing Over · Crossing over
Exchange of corresponding DNA segments between nonsister chromatids of homologous chromosomes during meiosis.
Crossing The blood–brain barrier · Crossing the blood–brain barrier
A delivery challenge because many therapeutic proteins and other large molecules do not readily enter the brain from blood.
Delivering Therapeutic oligonucleotides · Delivering therapeutic oligonucleotides
Getting an antisense or siRNA drug into the right tissue, cell, and intracellular compartment.
DNA Repair · DNA repair
Cellular systems that detect and fix many forms of DNA damage.
Endocytosis
A family of processes that internalize extracellular material or plasma-membrane components into membrane-bound vesicles.
Endosomal Escape · Endosomal escape
The release of internalized therapeutic molecules from endosomes into the cytoplasm or other site where their target resides.
Exon Skipping · Exon skipping
A splicing strategy that omits a selected exon from pre-mRNA, sometimes restoring the reading frame of a disease-associated transcript.
Fatty Acid synthesis · Fatty acid synthesis in human metabolism
In the fed state, cytosolic acetyl-CoA is converted to malonyl-CoA. Fatty acid synthase uses an acetyl primer, repeated malonyl additions, and NADPH to build palmitate, which can then be elongated or desaturated.
Fatty Acid β-oxidation · Fatty acid β-oxidation in human metabolism
Mitochondrial beta-oxidation repeatedly oxidizes, hydrates, oxidizes again, and cleaves fatty acyl-CoA. Each complete turn shortens the chain by two carbons and yields acetyl-CoA, NADH, and electrons that reach ubiquinone.
Fatty-acid Oxidation · Fatty-acid oxidation
The stepwise breakdown of fatty acids that supplies acetyl-CoA and electron carriers to other pathways.
Feedback In signaling · Feedback in signaling
Signals can feed back to strengthen, weaken, or reshape the pathway that produced them.
Feedback Inhibition · Feedback inhibition
A control pattern in which a later product reduces activity earlier in the process that makes it.
Gene Expression · Gene expression
The regulated use of information in a gene to make functional RNA or, for protein-coding genes, protein.
Gene Regulation · Gene regulation
How cells control when, where, and how strongly genes are used.
GLP-1 Receptor signaling · GLP-1 receptor signaling
Signaling through a class B GPCR activated by glucagon-like peptide 1 and related agonists.
Gluconeogenesis · Gluconeogenesis in human metabolism
Gluconeogenesis makes glucose from lactate, glycerol, and glucogenic amino acids, mainly in liver and kidney. It bypasses the three irreversible glycolysis reactions and shares the other reversible steps in the opposite direction.
GLUT4 Glucose uptake · GLUT4 glucose uptake
Insulin and muscle contraction can move GLUT4 transporters to the surface of muscle and adipose cells.
Glycogen Metabolism · Glycogen metabolism in human metabolism
Glycogen metabolism stores glucose when it is plentiful and mobilizes the branched polymer between meals or during muscle work. Liver glycogen can support blood glucose; muscle glycogen is used locally.
Glycogen Storage and breakdown · Glycogen storage and breakdown
How cells build glycogen from glucose and break it down when glucose or energy is needed.
GPCR Signaling · GPCR signaling
How G-protein-coupled receptors convert outside signals into intracellular changes.
Graded Potential · Graded potential
A local change in membrane voltage whose size varies with the input and that can spread passively over a limited distance.
Gs–cAMP–PKA Signaling · G alpha(s)-coupled receptor signaling through cyclic AMP and protein kinase A
A common GPCR branch in which Gαs stimulates cyclic AMP production and cAMP regulates protein kinase A and other effectors.
Heme Biosynthesis · human heme biosynthetic pathway
A multi-step route builds heme, the iron-containing cofactor used by hemoglobin and many other proteins.
Homeostasis
Regulation that keeps internal conditions within ranges compatible with organism function despite ongoing change.
Horizontal Gene transfer · Horizontal gene transfer
Movement of genetic material between organisms outside parent-to-offspring inheritance.
How Statins lower cholesterol · How statins lower cholesterol
Statins inhibit HMG-CoA reductase and can increase hepatic uptake of LDL from the circulation.
Independent Assortment · Independent assortment
The largely independent orientation and segregation of different homologous chromosome pairs during meiosis I.
Innate Immune Response
Rapid, pattern-based defenses that limit infection and help activate adaptive immunity.
Insulin Signaling · Insulin signaling
How insulin receptor signaling coordinates glucose uptake and nutrient storage.
Intracellular Oxygen transport · globin-mediated oxygen binding in cells
Globin proteins bind oxygen reversibly; hemoglobin carries it in blood, while myoglobin stores and moves oxygen within muscle.
JAK–STAT Signaling · JAK–STAT signaling
A direct route from selected cytokine receptors to transcriptional responses.
Kidney Metabolism · Kidney metabolism
The kidney supports transport-intensive work and can contribute to glucose production during fasting.
LDL Clearance and PCSK9 · Human LDL receptor-mediated clearance and PCSK9-dependent receptor degradation
An LDLR trafficking route that helps clear LDL particles from circulation and is regulated by PCSK9.
Light-dependent Reactions · Light-dependent reactions
Thylakoid-membrane reactions that convert absorbed light into ATP and NADPH while oxidizing water and releasing oxygen.
Liver Metabolism · Liver metabolism
The liver coordinates blood glucose, fuel storage and release, lipid metabolism, and nitrogen disposal.
Mannose-6-phosphate Lysosomal targeting · Mannose-6-phosphate lysosomal targeting
A sorting signal used by many soluble lysosomal enzymes to reach lysosomes through receptor-mediated trafficking.
Meiosis
Two coordinated divisions that reduce chromosome-set number and generate genetically varied haploid cells in sexual life cycles.
Membrane Transport · Membrane transport
How molecules cross cell membranes through channels, carriers, and pumps.
Mendelian Inheritance · Mendelian inheritance
Inheritance patterns explained by allele segregation and, for unlinked genes, independent assortment.
Mitosis
Eukaryotic nuclear division that separates replicated chromosomes into two daughter nuclei.
Nondisjunction
An error in chromosome segregation that can produce cells with an abnormal number of chromosomes.
Oxidation And reduction · Oxidation and reduction
Paired chemical changes in which electrons move from one molecule to another.
Oxidative Phosphorylation · Oxidative phosphorylation in human metabolism
The respiratory chain transfers electrons from NADH and FAD-linked sources to oxygen. Complexes I, III, and IV pump protons; ATP synthase uses the proton-motive force to make ATP from ADP and phosphate.
Oxidative Phosphorylation · Oxidative phosphorylation
Mitochondrial ATP production driven by electron transport and a proton gradient across the inner membrane.
Oxidative Stress · imbalance between oxidant challenge and cellular defenses
Oxidative stress describes a redox disturbance in which oxidant production or exposure exceeds the capacity of protective systems.
Oxygen Exchange in red blood cells · O2/CO2 exchange in erythrocytes
Hemoglobin takes up oxygen in the lungs and releases it in body tissues while red blood cells help transport carbon dioxide in the opposite direction.
p53 Signaling · p53-dependent stress response
A connected response in which stress signals stabilize p53 and influence cell-cycle arrest, repair, or apoptosis.
Passive Membrane transport · Passive membrane transport
Movement across a membrane down a concentration or electrochemical gradient without direct energy input from ATP hydrolysis.
Pentose Phosphate pathway · Pentose phosphate pathway in human metabolism
The pentose phosphate pathway branches from glucose 6-phosphate. Its oxidative branch makes NADPH and ribulose 5-phosphate; its reversible non-oxidative reactions interconvert pentoses with glycolytic intermediates to match biosynthetic demand.
Phenylalanine Metabolism · Phenylalanine metabolism
An amino-acid route that includes conversion of phenylalanine to tyrosine by PAH.
PI3K-AKT-mTOR Signaling · Human PI3K-AKT-mTOR signaling network
A growth- and nutrient-responsive network in which PI3K lipid signals regulate AKT and connect with mTORC1, metabolism, survival, and biosynthesis.
Protein Folding and Quality Control
How a protein chain adopts and maintains a functional structure, with cellular systems handling misfolded products.
Protein Phosphorylation · Protein phosphorylation
A reversible chemical modification that can change a protein's activity or interactions.
Purine Nucleotide synthesis · Purine nucleotide synthesis in human metabolism
De novo purine synthesis builds the purine ring atom by atom on activated ribose phosphate. The pathway makes IMP, which branches to AMP and GMP. Ring atoms come from glycine, glutamine, aspartate, carbon dioxide, and folate-bound one-carbon units.
Pyrimidine Nucleotide synthesis · Pyrimidine nucleotide synthesis in human metabolism
De novo pyrimidine synthesis builds the ring first, then attaches it to activated ribose. CAD performs the first three reactions, dihydroorotate dehydrogenase forms orotate at the inner mitochondrial membrane, and UMPS produces UMP.
Pyruvate Oxidation · Pyruvate oxidation in human metabolism
The pyruvate dehydrogenase complex links glycolysis to the citric acid cycle by converting pyruvate to acetyl-CoA. It releases carbon dioxide and captures electrons in NADH; its reaction is effectively irreversible in cells.
RAS-RAF-MEK-ERK Signaling (MAPK) · Human RAF/MAP kinase cascade
A growth-signal network whose core RAS-RAF-MEK-ERK relay regulates cell responses, with output shaped by feedback, location, and cell context.
Receptor Tyrosine kinase signaling · Receptor tyrosine kinase signaling
How growth-factor receptors use phosphorylation to assemble signaling networks.
Red Blood cell metabolism · Red blood cell metabolism
Mature red blood cells use glucose for ATP and reducing power because they lack mitochondria.
RNA Interference · RNA interference
A cellular process in which small RNAs guide protein complexes to reduce or regulate matching RNA molecules.
RNA Processing · RNA processing
How many eukaryotic RNA transcripts are modified before they are used.
RNase H1-Dependent ASO Cleavage
A gapmer antisense oligonucleotide binds a complementary RNA sequence and recruits RNase H1 to cleave the RNA strand of the hybrid.
Signal Amplification · Signal amplification
A signaling process in which one activated component influences many downstream molecules.
Skeletal Muscle metabolism · Skeletal muscle metabolism
Muscle uses circulating and stored fuels to meet the changing energy demand of contraction.
Steric-Blocking ASO Mechanisms
An antisense oligonucleotide binds RNA and blocks access by selected molecular partners, potentially changing splicing, translation, or RNA stability without RNase H1 cleavage.
Substrate-level Phosphorylation · Substrate-level phosphorylation
Direct formation of ATP or GTP when an enzyme transfers a phosphate group from a reaction intermediate.
Synaptic Transmission · Synaptic transmission
Communication from a neuron to another cell at a specialized junction, often using neurotransmitter release and receptors.
TGF-β Signaling · TGF-β signaling
A receptor-kinase network that regulates development, immune responses, and tissue remodeling.
The Small GTPase switch · The small GTPase switch
A molecular switch in which a small GTPase's bound GDP or GTP helps control its interactions with signaling partners.
Transcription
The process of making an RNA copy from a DNA template.
Urea Cycle · Urea cycle in human metabolism
The liver urea cycle packages two nitrogen atoms into urea for excretion. One nitrogen enters as mitochondrial ammonia and the other as cytosolic aspartate; ornithine is regenerated after each turn.
Vesicle Transport · Vesicle transport
Membrane-bound carriers that move selected cargo between compartments or to and from the cell surface.
Wnt Signaling · Wnt signaling
A family of signals with important roles in development, tissue renewal, and cell fate.