🧬 Biochemistry Glossary

A comprehensive reference of key biochemical terms — over 200 entries with quick alphabet navigation.

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A-DNA
A right-handed helical form of DNA with a wider, more compact structure than B-DNA; often found in dehydrated samples.
Abiotic
Non-living chemical and physical factors in the environment that can influence biochemical processes.
Acetyl-CoA
A central metabolite that carries acetyl groups in biochemical reactions; key in the Krebs cycle and fatty acid synthesis.
Acid Dissociation Constant (Ka)
A measure of the strength of an acid in solution, indicating its tendency to donate a proton.
Actin
A globular protein that forms microfilaments, essential for cell motility, structure, and muscle contraction.
Activation Energy
The minimum energy required to start a chemical reaction; enzymes lower this barrier.
Active Site
The region on an enzyme where substrate molecules bind and undergo a chemical reaction.
Adenine
A purine nucleobase that pairs with thymine (in DNA) or uracil (in RNA); a component of ATP.
Adenosine
A nucleoside composed of adenine and ribose; a building block of ATP, ADP, and AMP.
Adenylate Cyclase
An enzyme that catalyzes the conversion of ATP to cyclic AMP (cAMP), a second messenger.
ADP (Adenosine Diphosphate)
A nucleotide formed by the hydrolysis of ATP; it can be rephosphorylated to ATP.
Agonist
A molecule that binds to a receptor and activates it, producing a biological response.
Alanine
A non-essential amino acid involved in the glucose-alanine cycle; important for protein synthesis.
Allosteric Regulation
The regulation of an enzyme’s activity by binding a molecule at a site other than the active site.
Alpha Helix
A common secondary structure of proteins, a right-handed coiled conformation stabilized by hydrogen bonds.
Amino Acid
Organic compounds that combine to form proteins. They contain an amino group (-NH₂), a carboxyl group (-COOH), and a unique side chain (R group).
Amphipathic
Molecules that have both hydrophilic (water-loving) and hydrophobic (water-fearing) regions, such as phospholipids.
Anabolism
The set of metabolic pathways that construct larger molecules from smaller ones, requiring energy.
Anaerobic
Processes that occur without oxygen, such as glycolysis in anaerobic conditions.
Anticodon
A sequence of three nucleotides on a tRNA molecule that is complementary to a codon on mRNA.
Antioxidant
A molecule that inhibits oxidation and neutralizes free radicals, protecting cells from damage.
Apoptosis
Programmed cell death, a controlled process essential for development and tissue homeostasis.
Aqueous
Relating to or dissolved in water; the environment inside cells is aqueous.
Aromatic Amino Acids
Amino acids containing an aromatic ring, such as phenylalanine, tyrosine, and tryptophan.
ATP (Adenosine Triphosphate)
The primary energy carrier in all living organisms. It stores and transfers energy in its high-energy phosphate bonds.
ATP Synthase
An enzyme complex that synthesizes ATP from ADP and inorganic phosphate, driven by a proton gradient.
B-DNA
The most common form of DNA in cells, a right-handed helix with 10 base pairs per turn.
Base Pair
Two complementary nitrogenous bases (e.g., A-T, G-C) held together by hydrogen bonds in DNA or RNA.
Beta Sheet
A secondary protein structure where polypeptide chains are linked by hydrogen bonds in a sheet-like arrangement.
Bile Salts
Amphipathic molecules that emulsify fats in the digestive system, aiding in lipid absorption.
Biocatalysis
The acceleration of chemical reactions by biological catalysts, such as enzymes.
Bioenergetics
The study of energy flow through living systems, including ATP synthesis and metabolism.
Biomarker
A measurable indicator of a biological state or condition, often used in diagnostics.
Biomolecule
Any molecule produced by a living organism, including proteins, nucleic acids, lipids, and carbohydrates.
Biopolymer
A large polymer found in biological systems, such as proteins, DNA, and polysaccharides.
Biosynthesis
The process by which living organisms produce complex compounds from simpler precursors.
Biotin
A water-soluble B-vitamin (B7) that acts as a coenzyme in carboxylation reactions.
Buffer
A solution that resists pH changes upon addition of acid or base, crucial in maintaining physiological pH.
Calmodulin
A calcium-binding protein that mediates many cellular processes, including muscle contraction and neurotransmission.
Calvin Cycle
The set of biochemical reactions in photosynthesis that fix carbon dioxide into carbohydrates.
Carbohydrate
Biomolecules consisting of carbon, hydrogen, and oxygen (e.g., sugars, starches). They serve as energy sources and structural components.
Carboxyl Group
A functional group (-COOH) found in organic acids, including amino acids and fatty acids.
Catabolism
The breakdown of complex molecules into simpler ones, releasing energy.
Catalyst
A substance that increases the rate of a chemical reaction without being consumed. Enzymes are biological catalysts.
Cation
A positively charged ion; important in biochemistry for membrane potentials and enzyme activity.
Cell Membrane
A phospholipid bilayer with embedded proteins that separates the cell interior from the external environment.
Cell Signaling
The process by which cells communicate via chemical signals, including hormones and neurotransmitters.
Cellulose
A polysaccharide composed of β-glucose units; a major structural component of plant cell walls.
Centromere
The region of a chromosome where sister chromatids are joined and where spindle fibers attach during division.
Chaperone Protein
Proteins that assist in the proper folding of other polypeptides, preventing aggregation.
Chemiosmosis
The movement of ions across a selectively permeable membrane, driving ATP synthesis.
Chiral
A molecule that is not superimposable on its mirror image; amino acids are chiral except glycine.
Chitin
A polysaccharide of N-acetylglucosamine, found in the exoskeletons of arthropods and cell walls of fungi.
Cholesterol
A sterol that is a component of cell membranes and a precursor for steroid hormones and bile acids.
Chromatin
The complex of DNA and proteins (histones) that makes up chromosomes in eukaryotic cells.
Chromosome
A thread-like structure of nucleic acids and protein, carrying genetic information in the form of genes.
Chymotrypsin
A digestive enzyme that hydrolyzes peptide bonds, particularly at aromatic amino acid residues.
Citrate
A key intermediate in the Krebs cycle; also involved in fatty acid synthesis and regulation.
Cloning
The process of producing genetically identical copies of cells or organisms.
Coenzyme
An organic non-protein molecule that assists enzymes in catalysis, e.g., NAD+, FAD.
Cofactor
A non-protein chemical compound (metal ion or coenzyme) required for enzyme activity.
Collagen
A fibrous protein that is the main structural component of connective tissue, skin, and bones.
Complementary Base Pairing
The specific hydrogen bonding between adenine-thymine (or uracil) and guanine-cytosine in nucleic acids.
Conjugation
The transfer of genetic material between bacteria via direct cell-to-cell contact.
Cyclic AMP (cAMP)
A second messenger molecule involved in signal transduction pathways, derived from ATP.
Cysteine
A sulfur-containing amino acid that can form disulfide bonds, stabilizing protein structure.
Cytoplasm
The gel-like substance within a cell, excluding the nucleus, containing organelles and enzymes.
Cytosine
A pyrimidine nucleobase that pairs with guanine in DNA and RNA.
Deamination
The removal of an amino group from an amino acid, producing ammonia and a carbon skeleton.
Denaturation
The loss of the native structure of a protein or nucleic acid due to heat, pH, or chemicals.
Deoxyribose
The five-carbon sugar present in DNA, lacking one oxygen atom compared to ribose.
Desmosome
A cell junction that links cells together via intermediate filaments, providing mechanical strength.
Diabetes
A metabolic disorder characterized by high blood glucose levels due to insulin deficiency or resistance.
Dipeptide
A molecule consisting of two amino acids linked by a peptide bond.
DNA (Deoxyribonucleic Acid)
The molecule that carries genetic information. It consists of two strands forming a double helix, composed of nucleotide units.
DNA Ligase
An enzyme that joins DNA strands by forming phosphodiester bonds, essential in replication and repair.
DNA Polymerase
An enzyme that synthesizes DNA strands from deoxynucleotides during replication.
Domain (Protein)
A distinct structural or functional region within a protein that folds independently.
Double Helix
The structure of DNA, consisting of two coiled strands held together by hydrogen bonds.
Eicosanoids
Signaling molecules derived from fatty acids, including prostaglandins and leukotrienes.
Electron Transport Chain (ETC)
A series of protein complexes that transfer electrons, generating a proton gradient for ATP synthesis.
Electrophoresis
A technique that separates molecules (like DNA or proteins) based on size and charge using an electric field.
Endocytosis
The uptake of substances into a cell by invagination of the plasma membrane.
Endoplasmic Reticulum (ER)
An organelle involved in protein synthesis (rough ER) and lipid synthesis (smooth ER).
Energy Coupling
The use of energy released from exergonic reactions to drive endergonic reactions.
Enzyme
Proteins that act as biological catalysts, speeding up biochemical reactions. They are highly specific to their substrates.
Enzyme Kinetics
The study of the rates of enzyme-catalyzed reactions and how they are affected by various factors.
Epigenetics
Heritable changes in gene expression that do not involve changes in the DNA sequence.
Erythrocyte
A red blood cell, responsible for carrying oxygen and carbon dioxide.
Ester Bond
A bond formed between an alcohol and a carboxylic acid; found in lipids (triglycerides).
Eukaryote
An organism whose cells contain a nucleus and other membrane-bound organelles.
Exocytosis
The process by which cells expel materials by fusion of vesicles with the plasma membrane.
Exon
The coding region of a gene that is transcribed and translated into protein.
FAD (Flavin Adenine Dinucleotide)
A redox coenzyme involved in electron transfer in metabolic pathways like the Krebs cycle.
Fatty Acid
A carboxylic acid with a long hydrocarbon chain. They are key components of lipids and a major energy source.
Feedback Inhibition
A mechanism where the product of a pathway inhibits an earlier step, regulating metabolism.
Fermentation
An anaerobic metabolic process that regenerates NAD+ and produces ATP, yielding ethanol or lactate.
Fibrin
A protein involved in blood clotting, forming a mesh that stabilizes platelet plugs.
Fibrous Protein
Proteins with elongated, structural roles (e.g., collagen, keratin).
Fluorescence
The emission of light by a molecule after absorption of light; used in biochemical assays.
Folate
A B-vitamin (B9) essential for nucleotide synthesis and amino acid metabolism.
Fructose
A monosaccharide (fruit sugar) that is metabolized in the liver.
G Protein
A family of proteins that bind GTP and act as molecular switches in signal transduction.
Galactose
A monosaccharide that forms lactose with glucose; component of glycolipids.
Gamete
A haploid reproductive cell (sperm or egg) involved in sexual reproduction.
Gel Electrophoresis
A laboratory method to separate DNA, RNA, or proteins based on size and charge.
Gene
A sequence of DNA that encodes a functional product (RNA or protein).
Gene Expression
The process by which information from a gene is used to synthesize a functional product.
Genetic Code
The set of rules by which nucleotide triplets (codons) are translated into amino acids.
Genomics
The study of genomes, including mapping, sequencing, and functional analysis of genes.
Gluconeogenesis
The biosynthesis of glucose from non-carbohydrate precursors, such as amino acids.
Glucose
A simple sugar (monosaccharide) that is a primary energy source for cellular metabolism.
Glutamate
An amino acid that functions as a neurotransmitter and plays a role in metabolism.
Glycogen
A branched polysaccharide that stores glucose in animals and fungi.
Glycolysis
The metabolic pathway that converts glucose into pyruvate, generating ATP and NADH. It occurs in the cytoplasm.
Glycosylation
The enzymatic attachment of carbohydrates to proteins or lipids, affecting function and stability.
Golgi Apparatus
An organelle that modifies, sorts, and packages proteins and lipids for secretion.
Guanine
A purine nucleobase that pairs with cytosine in nucleic acids.
GTP (Guanosine Triphosphate)
A nucleotide involved in energy transfer and signal transduction; similar to ATP.
Heme
A prosthetic group containing iron that is found in hemoglobin and cytochromes.
Hemoglobin
A protein in red blood cells that transports oxygen from the lungs to tissues.
Heparin
A glycosaminoglycan that acts as an anticoagulant by binding to antithrombin.
Heterochromatin
Tightly packed chromatin that is transcriptionally inactive.
Hexokinase
An enzyme that catalyzes the phosphorylation of glucose, trapping it inside the cell.
Histone
Proteins that package DNA into nucleosomes, playing a role in gene regulation.
Homeostasis
The maintenance of a stable internal environment in an organism, regulated by biochemical feedback mechanisms.
Hormone
A signaling molecule released into the blood that regulates physiological processes.
Hydrogen Bond
A weak bond between a hydrogen atom and an electronegative atom, important in DNA and protein structure.
Hydrolysis
A chemical reaction in which water is used to break down a compound. It is essential in digestion and metabolism.
Hydrophilic
Substances that dissolve in water, typically polar or charged.
Hydrophobic
Substances that do not dissolve in water, typically nonpolar.
Hydroxyapatite
A mineral form of calcium phosphate found in bones and teeth.
Hyperglycemia
High blood glucose levels, often associated with diabetes.
Hypoglycemia
Low blood glucose levels, which can cause symptoms like dizziness and confusion.
Inhibitor
A molecule that decreases enzyme activity, either competitively or non-competitively.
Inositol
A sugar alcohol that is a component of phospholipids and involved in cell signaling.
Insulin
A peptide hormone that regulates blood glucose by promoting cellular uptake of glucose.
Integral Protein
A protein that is embedded in the cell membrane, often spanning the bilayer.
Interleukin
A type of cytokine that mediates immune responses and inflammation.
Intermediate Filament
Structural components of the cytoskeleton, providing mechanical support.
Intron
A non-coding sequence within a gene that is removed during RNA splicing.
Ion Channel
Protein pores in cell membranes that allow specific ions to pass through, critical for nerve signaling and muscle contraction.
Ion Pump
A protein that transports ions across a membrane against a concentration gradient using ATP.
Isoelectric Point
The pH at which a molecule carries no net electrical charge.
Isomerase
An enzyme that catalyzes the rearrangement of atoms within a molecule (e.g., glucose-6-phosphate isomerase).
Keratin
A fibrous protein that forms the structural basis of hair, nails, and skin.
Ketone Body
Water-soluble molecules (acetoacetate, beta-hydroxybutyrate) produced during fatty acid metabolism.
Kinase
An enzyme that transfers phosphate groups from ATP to a substrate (protein kinase).
Krebs Cycle (Citric Acid Cycle)
A series of chemical reactions used by aerobic organisms to generate energy through the oxidation of acetyl-CoA.
Lactate
The ionized form of lactic acid; produced during anaerobic glycolysis.
Lactose
A disaccharide composed of glucose and galactose; present in milk.
Laminin
A protein component of the extracellular matrix, important for cell adhesion.
Ligand
A molecule that binds to a receptor or protein, often initiating a signal.
Ligase
An enzyme that joins two molecules together, often using ATP; e.g., DNA ligase.
Lipase
An enzyme that catalyzes the hydrolysis of lipids into fatty acids and glycerol.
Lipid
Hydrophobic or amphipathic molecules including fats, oils, waxes, and steroids. They store energy and form membranes.
Lipid Bilayer
A double layer of phospholipids that forms the basic structure of cell membranes.
Lipoprotein
A complex of lipids and proteins that transports lipids in the blood.
Lysine
An essential amino acid important for protein synthesis and collagen formation.
Lysosome
A membrane-bound organelle containing digestive enzymes for intracellular breakdown.
Macromolecule
A large molecule, such as a protein, nucleic acid, or polysaccharide.
Magnesium (Mg²⁺)
A divalent cation that acts as a cofactor for many enzymes, including kinases.
Maltose
A disaccharide composed of two glucose units; produced by starch digestion.
Messenger RNA (mRNA)
RNA that carries genetic information from DNA to the ribosome for protein synthesis.
Metabolism
The sum of all chemical reactions occurring in an organism, including catabolism and anabolism.
Metabolite
A small molecule that is a substrate or product of metabolism.
Methylation
The addition of a methyl group to DNA or proteins, affecting gene expression and function.
MicroRNA (miRNA)
Small non-coding RNA molecules that regulate gene expression post-transcriptionally.
Microtubule
Hollow cylindrical polymers of tubulin, involved in cell division and intracellular transport.
Mitochondria
Organelles that generate ATP through oxidative phosphorylation; the “powerhouse” of the cell.
Mitosis
Cell division that results in two genetically identical daughter cells.
Molecular Chaperone
Proteins that assist in the folding of other proteins, preventing misfolding.
Monosaccharide
A simple sugar that cannot be hydrolyzed further, e.g., glucose, fructose.
Mutagen
A physical or chemical agent that causes mutations in DNA.
Mutation
A change in the nucleotide sequence of DNA, which can affect gene function.
Myoglobin
An oxygen-binding protein found in muscle tissue, with higher affinity than hemoglobin.
NAD⁺ (Nicotinamide Adenine Dinucleotide)
A coenzyme that carries electrons in redox reactions, essential for metabolism.
NADP⁺
A coenzyme used in anabolic reactions, such as fatty acid and nucleotide synthesis.
Neurotransmitter
A chemical messenger that transmits signals across synapses between neurons.
Nitrogen Fixation
The conversion of atmospheric nitrogen into ammonia by microbes, essential for biosynthesis.
Nucleotide
The building block of nucleic acids (DNA and RNA), consisting of a sugar, phosphate, and a nitrogenous base.
Nucleus
The organelle that contains the cell’s genetic material and controls gene expression.
Oligosaccharide
A carbohydrate composed of a small number of monosaccharides (3–10 units).
Oncogene
A gene that has the potential to cause cancer when mutated or overexpressed.
Organelle
A membrane-bound structure within a cell that performs a specific function.
Osmosis
The movement of water across a semipermeable membrane from low to high solute concentration.
Oxidation
The loss of electrons or increase in oxidation state. Often coupled with reduction in biochemical redox reactions.
Oxidative Phosphorylation
The process by which ATP is synthesized using the energy from electron transport in the mitochondria.
Oxygenase
An enzyme that incorporates oxygen into a substrate, often involved in biosynthesis.
p53
A tumor suppressor protein that regulates the cell cycle and prevents cancer.
Peptide Bond
The covalent bond linking amino acids in a protein, formed between the carboxyl and amino groups.
pH
A measure of hydrogen ion concentration. Enzymes and biochemical processes are highly sensitive to pH changes.
Phagocytosis
The process by which cells engulf large particles, such as pathogens, into vesicles.
Phenylalanine
An essential aromatic amino acid that is a precursor to tyrosine and neurotransmitters.
Phospholipid
A lipid with a phosphate head and fatty acid tails, forming the basis of cell membranes.
Phosphorylation
The addition of a phosphate group to a molecule, often used to regulate enzyme activity.
Photosynthesis
The process by which plants, algae, and some bacteria convert light energy into chemical energy.
Plasmid
A small, circular DNA molecule found in bacteria, often used in genetic engineering.
Polymerase
An enzyme that synthesizes polymers of nucleic acids or proteins.
Polypeptide
A chain of amino acids linked by peptide bonds; a protein may consist of one or more polypeptides.
Polysaccharide
A carbohydrate polymer composed of many monosaccharide units (e.g., glycogen, starch).
Porphyrin
A ring-shaped molecule that binds metal ions, such as heme in hemoglobin.
Primary Structure
The linear sequence of amino acids in a protein.
Prion
An infectious protein that misfolds and propagates, causing neurodegenerative diseases.
Prokaryote
An organism lacking a nucleus and membrane-bound organelles, such as bacteria.
Prosthetic Group
A tightly bound cofactor that is essential for enzyme activity, such as heme.
Protease
An enzyme that hydrolyzes peptide bonds in proteins.
Protein
Macromolecules composed of amino acid chains folded into specific 3D structures. They perform a vast array of functions.
Protein Kinase
An enzyme that phosphorylates proteins, regulating their activity.
Proteoglycan
Proteins with glycosaminoglycan chains, important in the extracellular matrix.
Proteome
The entire set of proteins expressed by a cell or organism at a given time.
Proton
A subatomic particle with a positive charge; in biochemistry, often refers to a hydrogen ion (H⁺).
Proton Gradient
An electrochemical gradient of protons across a membrane, driving ATP synthesis.
Purine
A nitrogenous base with a double-ring structure (adenine, guanine).
Pyrimidine
A nitrogenous base with a single-ring structure (cytosine, thymine, uracil).
Pyruvate
The end product of glycolysis; can enter the Krebs cycle or be converted to lactate.
Quaternary Structure
The assembly of multiple polypeptide chains into a functional protein complex.
Receptor
A protein that binds a ligand and transmits a signal into the cell.
Redox Reaction
A reaction involving the transfer of electrons between two species (reduction and oxidation).
Reduction
The gain of electrons or decrease in oxidation state.
Replication
The process by which DNA is copied before cell division.
Repressor
A protein that binds to DNA and inhibits transcription of a gene.
Ribose
A five-carbon sugar present in RNA.
Ribosome
The molecular machine that synthesizes proteins by translating mRNA.
RNA (Ribonucleic Acid)
A nucleic acid that plays roles in coding, decoding, regulation, and expression of genes. It is usually single-stranded.
RNA Polymerase
An enzyme that synthesizes RNA from a DNA template during transcription.
Saturated Fatty Acid
A fatty acid with no double bonds; solid at room temperature.
Second Messenger
A small molecule (e.g., cAMP, Ca²⁺) that relays signals from receptors to target molecules.
Secondary Structure
Local folded structures in proteins, such as alpha helices and beta sheets.
Signal Peptide
A short amino acid sequence that directs a protein to its cellular destination.
Signal Transduction
The process by which a cell converts an extracellular signal into a cellular response.
Small Interfering RNA (siRNA)
Small RNA molecules that interfere with gene expression by degrading mRNA.
Sodium-Potassium Pump
An ion pump that maintains electrochemical gradients by exchanging Na⁺ and K⁺ across the membrane.
Splicing
The removal of introns and joining of exons in pre-mRNA to form mature mRNA.
Starch
A polysaccharide of glucose used for energy storage in plants.
Steroid
A lipid molecule with a four-ring structure; includes cholesterol, hormones, and bile acids.
Substrate
The reactant molecule upon which an enzyme acts. The enzyme binds to its substrate to form an enzyme-substrate complex.
Substrate-Level Phosphorylation
ATP formation directly from ADP and a phosphorylated intermediate, without the ETC.
Succinate
A four-carbon intermediate in the Krebs cycle, involved in electron transfer.
Sucrose
A disaccharide composed of glucose and fructose; table sugar.
Synapse
The junction between neurons where neurotransmitters transmit signals.
Telomere
Repetitive nucleotide sequences at chromosome ends that protect them from degradation.
Tertiary Structure
The overall three-dimensional structure of a single polypeptide chain.
Thymine
A pyrimidine nucleobase that pairs with adenine in DNA.
Transcription
The synthesis of RNA from a DNA template by RNA polymerase.
Transcription Factor
Proteins that bind to DNA and regulate transcription, controlling gene expression.
Translation
The process by which ribosomes synthesize proteins from mRNA sequences.
Transmembrane Protein
A protein that spans the cell membrane, often acting as a channel or receptor.
Triglyceride
A lipid composed of glycerol and three fatty acids; the main form of fat storage.
tRNA (Transfer RNA)
RNA molecules that carry amino acids to the ribosome during translation.
Tryptophan
An essential aromatic amino acid; a precursor to serotonin and niacin.
Tyrosine
A non-essential amino acid derived from phenylalanine; precursor to neurotransmitters and hormones.
Ubiquitin
A small protein that tags other proteins for degradation by the proteasome.
Unsaturated Fatty Acid
A fatty acid with one or more double bonds; liquid at room temperature.
Uracil
A pyrimidine nucleobase present in RNA, replacing thymine.
Urea
A waste product from nitrogen metabolism, excreted in urine.
Valine
An essential branched-chain amino acid important for muscle metabolism.
Vector (Molecular)
A DNA molecule used to carry foreign genetic material into a host cell.
Vesicle
A small membrane-bound sac that transports substances within a cell.
Virion
A complete virus particle, consisting of nucleic acid and a protein coat.
Vitamin
An organic molecule required in small amounts for metabolism, often as a coenzyme precursor.
Watson-Crick Base Pairing
The specific hydrogen bonding between A-T (or A-U) and G-C in nucleic acids.
Xanthine
A purine base that is a breakdown product of adenine and guanine metabolism.
Xenobiotic
A chemical compound that is foreign to an organism, often metabolized by enzymes.
Y chromosome
The sex chromosome that determines male sex in mammals.
Yeast
A eukaryotic microorganism used in fermentation and as a model organism in biochemistry.
Z-DNA
A left-handed helical form of DNA, with a zigzag backbone.
Zinc Finger
A protein structural motif that binds zinc and interacts with DNA, often in transcription factors.
Zwitterion
A molecule with both positive and negative charges but net neutral, such as amino acids at physiological pH.
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