Biochemistry is the study of the chemical substances, molecular structures and chemical reactions that occur in living organisms. It combines principles of chemistry with biological questions and examines how molecules such as proteins, nucleic acids, lipids, carbohydrates, metabolites and inorganic ions interact to sustain cellular life. Biochemistry explains processes including enzyme catalysis, energy production, biosynthesis, molecular signalling, DNA replication and degradation of nutrients. It operates across scales from individual chemical bonds to integrated metabolic pathways and cellular networks.
Whereas Chemistry studies matter and chemical reactions generally, Biochemistry focuses particularly on chemical processes in biological systems and the distinctive constraints imposed by cellular organisation, aqueous environments, temperature, pH and biological regulation. Biochemistry consequently provides much of the mechanistic foundation for understanding physiology, Cell Biology and Molecular Biology.
Proteins are among the most important biochemical macromolecules. They consist of amino-acid chains whose sequences determine tendencies to fold into particular structures and interact with other molecules. Protein functions include catalysis, transport, structural support, movement, recognition, signalling and regulation. Enzymes are catalytic proteins in most biological systems, although some RNA molecules also have catalytic activity. Enzymes increase reaction rates by providing pathways with lower activation-energy barriers and often show high specificity for particular substrates or reaction types. Enzyme activity can be influenced by temperature, pH, substrate concentration, cofactors, inhibitors and regulatory molecules. Michaelis-Menten kinetics provides a classical framework for analysing many enzyme-catalysed reactions, although real biological systems often exhibit more complicated kinetics involving multiple substrates, allosteric regulation or cooperative behaviour.
Nucleic acids are central biochemical molecules for storing, transmitting and expressing genetic information. DNA and RNA consist of nucleotide building blocks containing sugars, phosphate groups and nitrogenous bases. Their chemical structures permit complementary base pairing, which supports processes such as DNA replication and RNA interactions. RNA has numerous functions beyond serving as an intermediary in protein synthesis, including structural, catalytic and regulatory roles.
Biochemistry also examines nucleotide metabolism, including synthesis and degradation of nucleotides and the role of nucleotide triphosphates such as ATP in cellular energy transfer. The chemical properties of nucleic acids influence their stability, folding, interactions with proteins and susceptibility to damage. These properties provide the molecular basis for many techniques used in molecular biology and biotechnology.
Lipids are chemically diverse molecules that include fatty acids, triglycerides, phospholipids, sterols and other hydrophobic or amphipathic compounds. Phospholipids are major components of biological membranes because their amphipathic structures permit formation of bilayers in aqueous environments. Lipids also function as energy stores, signalling molecules, membrane components and precursors for other biologically active substances. Carbohydrates include simple sugars and larger polymers and participate in energy metabolism, storage, molecular recognition and structural functions. Glycoproteins and glycolipids contain carbohydrate components attached to proteins or lipids and contribute to cell recognition and communication. The biological roles of these molecule classes depend heavily on their chemical structures, demonstrating why Biochemistry must consider molecular architecture as well as gross composition.
Cellular reactions occur within interconnected networks rather than as isolated chemical events. Metabolic pathways consist of sequences of enzyme-catalysed reactions in which products can become substrates for subsequent steps. Pathways can be linear, branched, cyclic or organised into larger networks. Cells regulate pathway activity through enzyme abundance, allosteric control, covalent modification, substrate availability, compartmentalisation and hormonal signalling. Thermodynamics determines whether reactions are energetically favourable under particular conditions, while kinetics determines how rapidly reactions proceed. ATP is a major energy-transfer molecule, but cells also use reducing equivalents such as NADH and NADPH to transfer electrons. Redox reactions are central to energy metabolism and biosynthesis because controlled electron transfer can be coupled to energy conservation.
Biochemical reactions occur in controlled chemical environments. pH affects the ionisation state of molecules and can substantially alter enzyme activity and protein structure. Buffers resist changes in hydrogen-ion concentration and help maintain suitable conditions within cells and experimental systems. Metal ions can function as structural components or enzyme cofactors, while organic cofactors derived from vitamins can participate in catalytic reactions. Water is both solvent and reactant in many biological processes, including hydrolysis. Molecular interactions include hydrogen bonds, ionic interactions, hydrophobic effects and van der Waals forces. Individually these interactions may be relatively weak, but their combined effects determine molecular recognition, protein folding, membrane assembly and macromolecular complexes.
Biochemical research uses a wide range of analytical methods. Chromatography separates molecules according to properties such as size, charge, polarity or affinity. Electrophoresis separates nucleic acids or proteins, while mass spectrometry can identify and quantify molecules based on mass-to-charge ratios. Spectroscopy measures interactions between matter and electromagnetic radiation and can provide information about concentration or molecular structure. Enzyme assays measure catalytic activity, while calorimetric and structural methods can investigate molecular interactions and thermodynamic properties.
Recombinant protein expression permits production of selected proteins for study, and structural methods reveal how molecular shape relates to function. Biochemical experiments require controls, appropriate standards and careful consideration of reaction conditions because changes in concentration, temperature, pH or sample purity can substantially affect results.
Biochemistry has extensive applications in medicine, nutrition, pharmacology and biotechnology. Clinical biochemistry measures substances in biological samples to assist diagnosis or monitoring, including enzymes, electrolytes, metabolites, hormones and proteins. Pharmacology frequently depends on understanding how drugs interact chemically with enzymes, receptors, transporters and other molecular targets. Nutritional biochemistry examines how nutrients are absorbed, transformed and incorporated into biological pathways. Biotechnology uses enzymes and metabolic pathways for industrial production of pharmaceuticals, food ingredients, chemicals and other materials. Biochemistry also helps explain disease mechanisms by identifying how mutations, toxins, nutrient deficiencies or altered regulation disrupt molecular reactions. Its central role is to connect the chemical properties of biological molecules with the organised processes that sustain cells and organisms.
