CELLS

Index of Terms and Definitions

Atoms and Subatomic Particles

• 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 (-).

Structure of Atoms

• 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 Bonds and Compounds

• 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.

Chemical Reactions

• 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.

Inorganic Compounds

• 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.

Acids, Bases, and pH

• 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.

Electrolytes and Salts

• 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⁻).

Organic Compounds

• 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.

• Enzyme Function:

• 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 Acids

• 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.

High-Energy Compounds

• 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.