CELLS

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.