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Atom
The smallest unit of an element.
Proton
A subatomic particle with a positive charge (+).
Neutron
A subatomic particle with no charge (neutral).
Electron
A subatomic particle with a negative charge (-).
Nucleus
The central part of an atom containing protons and neutrons.
Electron Shell
The region around the nucleus where electrons are found.
Atomic Number
The number of protons in an atom.
Atomic Mass
The sum of protons and neutrons in an atom.
Isotopes
Variants of an element differing in neutron count.
Atomic Weight
The average mass of an element’s isotopes based on abundance.
Chemical Bond
The force that holds atoms together in a molecule.
Ionic Bond
A bond formed when electrons are transferred between atoms, creating charged ions.
Cation
A positively charged ion (+).
Anion
A negatively charged ion (-).
Covalent Bond
A bond where atoms share electrons.
Nonpolar Covalent Bond
Equal sharing of electrons (e.g., carbon-carbon bonds).
Polar Covalent Bond
Unequal sharing of electrons (e.g., oxygen-hydrogen bonds).
Hydrogen Bond
A weak attraction between a hydrogen atom and an oxygen/nitrogen atom.
Metabolism
The sum of all chemical reactions in the body.
Reactants
Substances that participate in a chemical reaction.
Products
Substances formed in a chemical reaction.
Decomposition Reaction
A reaction that breaks molecules into smaller parts (AB → A + B).
Synthesis Reaction
A reaction that combines smaller molecules into larger ones (A + B → AB).
Exchange Reaction
A reaction where molecular components are swapped (AB + CD → AC + BD).
Reversible Reaction
A reaction that can proceed in both directions (A + B ⇌ AB).
Enzyme
A protein that speeds up chemical reactions by lowering activation energy.
Activation Energy
The energy required to start a chemical reaction.
Exergonic Reaction
A reaction that releases energy.
Endergonic Reaction
A reaction that absorbs energy.
Nutrient
Essential elements and molecules obtained from the diet.
Metabolite
A molecule synthesized or broken down in the body.
Inorganic Compound
A compound that lacks carbon-hydrogen bonds (e.g., water, oxygen).
Organic Compound
A compound containing carbon, hydrogen, and often oxygen.
Carbon Dioxide (CO₂)
A gas produced by metabolism and exhaled from the lungs.
Oxygen (O₂)
A gas necessary for cellular respiration.
Water (H₂O)
The most important chemical in the body, essential for life.
Acid
A substance that releases hydrogen ions (H⁺) in a solution.
Base
A substance that removes hydrogen ions from a solution.
pH Scale
A measure of hydrogen ion concentration in a solution (0-14).
Neutral
pH = 7
Acidic
pH < 7
Basic (Alkaline)
pH > 7
Buffer
A substance that helps maintain a stable pH in the body.
Salt
An ionic compound that does not contain H⁺ or OH⁻.
Electrolyte
A compound that dissociates in water to conduct electricity (e.g., NaCl → Na⁺ + Cl⁻).
Carbohydrate
The primary energy source for metabolism.
Monosaccharide
A simple sugar (e.g., glucose).
Disaccharide
Two linked monosaccharides (e.g., sucrose).
Polysaccharide
Multiple monosaccharides linked together (e.g., glycogen).
Lipid
A water-insoluble molecule used for energy storage and cell structure.
Fatty Acid
A long hydrocarbon chain with a carboxyl group.
Triglyceride
A lipid formed by three fatty acids and glycerol.
Steroid
A lipid with a four-ring structure (e.g., cholesterol).
Phospholipid
A major component of cell membranes with water-soluble and water-insoluble parts.
Protein
A molecule made of amino acids that performs various functions in the body.
Amino Acid
The building block of proteins.
Peptide Bond
A bond linking amino acids in a protein.
Protein Structure
The complex shape of a protein that determines its function.
Denaturation
The distortion of a protein’s shape due to high temperature or other factors.
Substrate
The reactant in an enzymatic reaction.
Active Site
The region on an enzyme where the substrate binds.
Catalyst
A substance that speeds up a chemical reaction without being consumed.
Nucleic Acid
A large molecule storing and processing genetic information.
DNA (Deoxyribonucleic Acid)
The molecule that contains genetic instructions.
RNA (Ribonucleic Acid)
The molecule involved in protein synthesis.
Nucleotide
The building block of nucleic acids, consisting of a sugar, phosphate, and base.
Double Helix
The two-stranded structure of DNA held together by hydrogen bonds.
ATP (Adenosine Triphosphate)
The primary energy carrier in cells.
ADP (Adenosine Diphosphate)
The lower-energy form of ATP.
Catabolism
The breakdown of molecules to release energy.
Anabolism
The synthesis of complex molecules using energy.
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