| Term | Definition |
|---|---|
| activation energy | The minimum energy required for a chemical reaction to proceed; enzymes lower this energy barrier to facilitate reactions. |
| active site | The specific region on an enzyme where the substrate binds and the chemical reaction is catalyzed. |
| biological catalysts | Substances that speed up biological reactions without being consumed in the process; enzymes are the primary biological catalysts in cells. |
| enzyme | Proteins that act as biological catalysts to speed up chemical reactions in cells by lowering activation energy. |
| enzyme-substrate complex | The temporary complex formed when a substrate binds to the active site of an enzyme during a catalyzed reaction. |
| substrate | The molecule or substance upon which an enzyme acts during a chemical reaction. |
| Term | Definition |
|---|---|
| active site | The specific region on an enzyme where the substrate binds and the chemical reaction is catalyzed. |
| allosteric site | A binding site on an enzyme other than the active site, where regulatory molecules can bind to affect enzyme activity. |
| cellular environment | The internal conditions of a cell, including temperature, pH, and concentrations of molecules, that affect enzyme function. |
| chemical environment | The composition of substances surrounding an enzyme that can affect its structure and function. |
| collision frequency | The rate at which enzyme and substrate molecules encounter each other in solution, affecting the rate of enzymatic reaction. |
| competitive inhibitor | A molecule that binds reversibly to the active site of an enzyme, competing with substrate for binding and reducing enzyme activity. |
| denaturation | The disruption of a protein's three-dimensional structure, causing loss of its biological function. |
| enzymatic reaction rate | The speed at which an enzyme catalyzes the conversion of substrate to product. |
| enzyme | Proteins that act as biological catalysts to speed up chemical reactions in cells by lowering activation energy. |
| enzyme activity | The rate at which an enzyme catalyzes a biochemical reaction under specific cellular conditions. |
| enzyme efficiency | The rate at which an enzyme catalyzes a reaction under given conditions. |
| enzyme function | The ability of an enzyme to catalyze specific biochemical reactions efficiently. |
| hydrogen bond | Weak attractive forces between a hydrogen atom bonded to an electronegative atom and another electronegative atom, occurring between or within biological molecules. |
| noncompetitive inhibitor | A molecule that binds to an allosteric site on an enzyme, changing the enzyme's shape and reducing its activity without competing with substrate. |
| optimal pH | The pH at which an enzyme exhibits maximum catalytic activity and efficiency. |
| optimal temperature | The temperature at which an enzyme exhibits maximum catalytic activity and efficiency. |
| product | The molecule produced as a result of an enzymatic reaction. |
| product concentration | The relative amount of product molecules present in a solution, which can affect the efficiency of an enzymatic reaction. |
| protein structure | The three-dimensional arrangement of amino acids in a protein, which determines its properties and function. |
| reversible denaturation | The process by which a denatured enzyme can regain its original structure and catalytic activity when environmental conditions are restored. |
| substrate | The molecule or substance upon which an enzyme acts during a chemical reaction. |
| substrate concentration | The relative amount of substrate molecules available for an enzyme to catalyze, which affects the rate of enzymatic reaction. |
| temperature | An environmental factor that affects the kinetic energy and collision frequency of molecules, influencing enzyme activity. |
| Term | Definition |
|---|---|
| cellular processes | Biochemical reactions and activities that occur within cells to maintain life and carry out functions. |
| common ancestry | The concept that all organisms share a common evolutionary origin and are related through descent from earlier ancestral species. |
| conserved process | Biological processes that are maintained relatively unchanged across different organisms and evolutionary time, indicating shared ancestry. |
| core metabolic pathways | Essential biochemical sequences that are conserved across different organisms and domains of life, such as glycolysis and oxidative phosphorylation. |
| coupled reactions | Cellular processes where energy-releasing reactions are linked to energy-requiring reactions to transfer energy efficiently. |
| domain | The three major categories of life (Archaea, Bacteria, and Eukarya) that represent the highest taxonomic rank in biological classification. |
| energy | The capacity to do work or cause change in living systems; required by all organisms to maintain order and power cellular processes. |
| energy transfer | The movement of energy from one form or location to another through sequential reactions in metabolic pathways. |
| first law of thermodynamics | The principle that energy cannot be created or destroyed, only transformed from one form to another. |
| glycolysis | A biochemical pathway in the cytosol that breaks down glucose and releases energy to form ATP, NADH, and pyruvate. |
| living systems | Organized biological entities that require energy input to maintain their structure and functions. |
| metabolic pathway | A series of sequential chemical reactions in cells where the product of one reaction serves as the reactant for the next reaction. |
| order | The organized, structured state of a living system that requires continuous energy input to maintain. |
| oxidative phosphorylation | The synthesis of ATP coupled to electron transport in the electron transport chain during aerobic cellular respiration. |
| second law of thermodynamics | The principle that in any energy transformation, some energy is lost as heat and disorder (entropy) in the universe increases. |
| Term | Definition |
|---|---|
| adenosine triphosphate | The primary energy currency of cells that powers cellular functions. |
| ADP | Adenosine diphosphate; a molecule that is phosphorylated to form ATP during oxidative phosphorylation. |
| ATP synthase | A membrane-bound enzyme that uses the proton gradient to drive the synthesis of ATP from ADP and inorganic phosphate. |
| Calvin cycle | The light-independent reactions of photosynthesis that use ATP and NADPH to produce carbohydrates from carbon dioxide in the stroma. |
| carbohydrates | Biological molecules composed of carbon, hydrogen, and oxygen that serve as a primary source of energy and structural support in living organisms. |
| carbon fixation | The process in the Calvin cycle that incorporates carbon dioxide into organic molecules. |
| chemiosmosis | The process by which the flow of protons across a membrane through ATP synthase drives ATP synthesis. |
| chlorophyll | A pigment in chloroplasts that absorbs light energy and transfers electrons to higher energy levels in photosystems. |
| chloroplast | An organelle in plant cells where photosynthesis occurs, containing thylakoids and stroma. |
| cyanobacteria | Prokaryotic photosynthetic organisms responsible for producing an oxygenated atmosphere through photosynthesis. |
| electrochemical gradient | The combined effect of the concentration gradient and electrical potential difference across a membrane that influences ion movement. |
| electron transport | A series of protein complexes in thylakoid membranes that transfer electrons and help generate ATP and NADPH during the light reactions. |
| electron transport chain | A series of protein complexes in membranes that transfer electrons and establish an electrochemical gradient to generate ATP during photosynthesis and cellular respiration. |
| grana | Stacks of thylakoid membranes organized within the chloroplast where light reactions of photosynthesis occur. |
| inorganic phosphate | A free phosphate group (Pi) that is added to ADP to form ATP during ATP synthesis. |
| light reactions | The light-dependent stage of photosynthesis that occurs in the thylakoid membrane and produces ATP and NADPH. |
| NADP⁺ | An electron carrier molecule that accepts electrons during photosynthesis and is reduced to NADPH to carry energy for the Calvin cycle. |
| NADPH | The reduced form of NADP⁺ that carries electrons and energy from the light reactions to power the Calvin cycle. |
| oxidation/reduction reactions | Chemical reactions in which electrons are transferred between molecules, occurring in the electron transport chain during photosynthesis. |
| photophosphorylation | The synthesis of ATP from ADP and inorganic phosphate using energy from the proton gradient established during the light reactions of photosynthesis. |
| photosynthesis | The series of reactions that use carbon dioxide, water, and light energy to produce carbohydrates and oxygen, allowing organisms to capture and store energy from the sun. |
| photosystem | Organized complexes of chlorophyll pigments and proteins in thylakoid membranes that capture light energy during the light reactions. |
| photosystem I | A light-harvesting complex embedded in the thylakoid membrane that uses light energy to boost electrons to a higher energy level and reduce NADP⁺ to NADPH. |
| photosystem II | A light-harvesting complex embedded in the thylakoid membrane that uses light energy to boost electrons and splits water to replace lost electrons. |
| prokaryotic photosynthesis | Photosynthetic processes in prokaryotic organisms, particularly cyanobacteria, that were the evolutionary foundation for eukaryotic photosynthesis. |
| proton gradient | A difference in proton concentration across a membrane, with higher concentration on one side than the other. |
| stroma | The fluid-filled space inside the chloroplast where the Calvin cycle occurs. |
| thylakoid | Membrane structures within the chloroplast that contain chlorophyll pigments and electron transport proteins, where light reactions occur. |
| thylakoid membrane | The membrane system within chloroplasts where light-dependent reactions of photosynthesis occur, containing photosystems and electron transport chains. |
| water splitting | The photolysis of water molecules during photosystem II that releases electrons, protons, and oxygen. |
| Term | Definition |
|---|---|
| adenosine triphosphate | The primary energy currency of cells that powers cellular functions. |
| ADP | Adenosine diphosphate; a molecule that is phosphorylated to form ATP during oxidative phosphorylation. |
| aerobic cellular respiration | The metabolic pathway that uses oxygen as the terminal electron acceptor to generate ATP from biological macromolecules. |
| ATP synthase | A membrane-bound enzyme that uses the proton gradient to drive the synthesis of ATP from ADP and inorganic phosphate. |
| biological macromolecules | Large organic molecules such as carbohydrates, lipids, and proteins that store chemical energy used in cellular respiration. |
| carbon dioxide | A gas released during the Krebs cycle as organic molecules are oxidized. |
| cellular respiration | The metabolic process by which cells break down biological macromolecules to release energy and synthesize ATP. |
| chemiosmosis | The process by which the flow of protons across a membrane through ATP synthase drives ATP synthesis. |
| decoupling | The separation of oxidative phosphorylation from electron transport, resulting in heat generation instead of ATP synthesis. |
| electrochemical gradient | The combined effect of the concentration gradient and electrical potential difference across a membrane that influences ion movement. |
| electron acceptor | A molecule that receives electrons during a redox reaction; oxygen is the terminal electron acceptor in aerobic respiration. |
| electron transport chain | A series of protein complexes in membranes that transfer electrons and establish an electrochemical gradient to generate ATP during photosynthesis and cellular respiration. |
| endothermic organisms | Organisms that generate and regulate their own body heat through metabolic processes. |
| enzyme-catalyzed reactions | Chemical reactions in cells that are accelerated by enzymes, which act as biological catalysts. |
| eukaryotes | Organisms whose cells contain a membrane-bound nucleus and other membrane-bound organelles. |
| FAD | A coenzyme that accepts electrons during the Krebs cycle, forming FADH₂. |
| FADH₂ | Flavin adenine dinucleotide (reduced form); an electron carrier that delivers electrons to the electron transport chain. |
| fermentation | An anaerobic metabolic process that regenerates ATP and NAD+ without using the electron transport chain or oxygen. |
| glucose | A six-carbon sugar whose energy is released through cellular respiration to power cellular functions. |
| glycolysis | A biochemical pathway in the cytosol that breaks down glucose and releases energy to form ATP, NADH, and pyruvate. |
| heat | Thermal energy generated when oxidative phosphorylation is uncoupled from electron transport in cellular respiration. |
| inner mitochondrial membrane | The innermost membrane of the mitochondrion that contains the electron transport chain and is the site of ATP synthesis. |
| inorganic phosphate | A free phosphate group (Pi) that is added to ADP to form ATP during ATP synthesis. |
| intermembrane space | The region between the inner and outer mitochondrial membranes where protons accumulate during the electron transport chain. |
| Krebs cycle | A biochemical cycle in the mitochondrial matrix that oxidizes pyruvate, releases CO₂, generates ATP, and transfers electrons via NAD⁺ and FAD. |
| lactic acid | An organic molecule produced during fermentation in the absence of oxygen. |
| mitochondria | Membrane-bound organelles in eukaryotic cells that are the primary site of aerobic cellular respiration and ATP synthesis. |
| mitochondrial matrix | The innermost compartment of the mitochondrion where the Krebs cycle occurs. |
| mitochondrion | An organelle where pyruvate is oxidized and ATP is generated through the Krebs cycle and electron transport chain. |
| NAD⁺ | A coenzyme that accepts electrons during glycolysis and the Krebs cycle, forming NADH. |
| NADH | Nicotinamide adenine dinucleotide (reduced form); an electron carrier that delivers electrons to the electron transport chain. |
| oxidation | The process of losing electrons, which occurs when pyruvate and other molecules are broken down in the Krebs cycle. |
| oxidation-reduction reactions | Chemical reactions involving the transfer of electrons between molecules, where one molecule is oxidized and another is reduced. |
| oxidative phosphorylation | The synthesis of ATP coupled to electron transport in the electron transport chain during aerobic cellular respiration. |
| oxygen | An element that is a prevalent component of biological molecules and is found in carbohydrates, lipids, proteins, and nucleic acids. |
| plasma membrane | The selectively permeable membrane that surrounds the cell, composed of phospholipids, proteins, and other molecules that regulate what enters and exits the cell. |
| prokaryotes | Single-celled organisms without a membrane-bound nucleus, such as bacteria and archaea. |
| proton gradient | A difference in proton concentration across a membrane, with higher concentration on one side than the other. |
| pyruvate | A three-carbon molecule produced from glycolysis that is transported to the mitochondrion for further oxidation. |