Overview
This lecture introduces the chemical foundations of the human body, including the structure and behavior of atoms, chemical bonds, energy in reactions, and the significance of both inorganic and organic compounds, especially as they relate to human physiology.
Composition of Matter
- Matter is anything that occupies space and has mass.
- Elements are pure substances that cannot be broken down by normal chemical means.
- The four most abundant elements in the human body are oxygen, carbon, hydrogen, and nitrogen.
- Atoms are the smallest units of elements, made of protons, neutrons, and electrons.
Atomic Structure and Stability
- Protons have a positive charge, neutrons are neutral, and electrons are negatively charged.
- The atomic number equals the number of protons and determines the element.
- Mass number equals protons plus neutrons.
- Isotopes are atoms of the same element with different numbers of neutrons; some are radioactive.
- Electrons occupy shells; stability is greatest when the outer shell is full (octet rule).
Chemical Bonds and Molecules
- Chemical bonds form when atoms interact via their valence electrons.
- Ionic bonds occur when electrons are transferred, forming charged ions (cations and anions).
- Covalent bonds involve sharing electrons; can be nonpolar (equal sharing) or polar (unequal sharing).
- Hydrogen bonds are weak bonds involving a hydrogen atom and an electronegative atom, important in water and biomolecules.
Chemical Reactions and Energy
- Chemical reactions involve breaking and forming bonds, exchanging matter and energy.
- Kinetic energy is energy of motion; potential (chemical) energy is stored in bonds.
- Exergonic reactions release energy; endergonic reactions require energy input.
- Synthesis (anabolic) reactions build larger molecules; decomposition (catabolic) reactions break them down.
- Enzymes (protein catalysts) speed up reactions by lowering activation energy.
Inorganic Compounds Essential to Life
- Inorganic compounds lack both carbon and hydrogen.
- Water acts as a lubricant, heat sink, medium for mixtures, and solvent for reactions.
- Salts dissociate into electrolytes, essential for nerve and muscle function.
- Acids release hydrogen ions (H+); bases release hydroxyl ions (OH−) or accept H+.
- pH measures solution acidity/alkalinity; buffers help maintain blood and tissue pH homeostasis.
Organic Compounds
- Organic compounds contain both carbon and hydrogen; main types are carbohydrates, lipids, proteins, nucleic acids.
- Carbohydrates (sugars and polymers) provide energy and cell structure.
- Lipids (fats, oils) store energy, insulate, and form cell membranes.
- Proteins (amino acid polymers) build tissues, catalyze reactions (enzymes), and regulate body functions.
- Nucleic acids (DNA, RNA) store and transmit genetic information; ATP carries energy within cells.
Key Terms & Definitions
- Atom — smallest unit of an element with its properties.
- Element — pure substance of one type of atom.
- Isotope — atom with the same number of protons but different neutrons.
- Ion — atom with a net charge due to gaining or losing electrons.
- Ionic bond — bond from transfer of electrons between ions.
- Covalent bond — bond from sharing electron pairs.
- Hydrogen bond — weak bond between a hydrogen atom and electronegative atom.
- Enzyme — protein that catalyzes (speeds up) chemical reactions.
- Electrolyte — ion in solution that conducts electricity.
- Buffer — chemical that stabilizes pH by neutralizing acids or bases.
- Monomer/Polymer — single unit/many connected units in macromolecules.
Action Items / Next Steps
- Review the periodic table, focusing on elements common to the human body.
- Complete assigned end-of-chapter questions on chemical bonding and macromolecules.
- Read about enzyme function and properties of water in preparation for the next class.