Chemical Organization & Molecules

Overview

This lecture covers the chemical level of organization, focusing on matter, atomic structure, chemical bonds, reactions, and the major classes of biological molecules essential for life.

Matter and Its Properties

• Matter has mass and occupies space; exists as solid, liquid, or gas.
• Solids have definite shape and volume; liquids have definite volume, variable shape; gases have variable shape and volume.
• Elements are pure substances that cannot be broken down by ordinary chemical means.

Elements and Atoms

• Major elements in the human body: oxygen (O), carbon (C), hydrogen (H), nitrogen (N).
• Atoms consist of protons (+), neutrons (0), and electrons (–).
• Atomic number = number of protons; mass number = protons + neutrons.
• Isotopes: atoms of same element with different neutron numbers; some are radioactive.

Chemical Bonds and Molecules

• Ions are charged atoms: cations (+, lost electron), anions (–, gained electron).
• Ionic bonds form by electron transfer; covalent bonds by electron sharing.
• Polar covalent bonds have unequal electron sharing (e.g., water); nonpolar have equal sharing.
• Hydrogen bonds occur between polar molecules and influence properties like water's surface tension.

Chemical Reactions and Energy

• Chemical reactions form or break bonds; reactants turn into products.
• Kinetic energy is energy of motion; potential energy is stored energy.
• Synthesis (anabolic), decomposition (catabolic), and exchange reactions are types of chemical reactions.
• Enzymes lower activation energy, speeding reaction rates; can be affected by temp, size, concentration, and pH.

Water, pH, and Buffers

• Water is the universal solvent; dissolves polar substances (hydrophilic), not nonpolar (hydrophobic).
• Electrolytes conduct electricity and are essential for functions like nerve signaling and muscle contraction.
• pH scale (0-14): acids (<7), bases (>7), neutral (7); acids donate H+, bases accept H+.
• Buffers stabilize pH by absorbing/releasing H+ ions.

Biological Macromolecules

Carbohydrates

• Contain C, H, O in 1:2:1 ratio; main function is energy (glucose).
• Monosaccharides (simple sugars), disaccharides (2 sugars), polysaccharides (many sugars, e.g., glycogen, starch).

Lipids

• Nonpolar molecules, insoluble in water, main types: fats, oils, waxes.
• Fatty acids can be saturated (no double bonds) or unsaturated (one/more double bonds).
• Triglycerides: glycerol + 3 fatty acids; phospholipids important for cell membranes; steroids have 4-ring structure.

Proteins

• Made of amino acids linked by peptide bonds; contain C, H, O, N (sometimes S, P).
• Four levels of structure: primary, secondary, tertiary, quaternary.
• Can be denatured by heat or pH; function as enzymes, structural materials, etc.

Nucleic Acids and ATP

• DNA and RNA are nucleic acids made of nucleotides (base + sugar + phosphate).
• DNA is double-stranded, stores genetic info; RNA is single-stranded, helps in protein synthesis.
• ATP is the cell’s energy currency, releases energy when phosphate bonds are hydrolyzed.

Key Terms & Definitions

• Element — Substance that cannot be chemically broken down.
• Isotope — Atom with same protons, different neutrons.
• Ion — Charged atom or molecule.
• Ionic bond — Bond from electron transfer between atoms.
• Covalent bond — Bond from sharing electrons.
• Hydrogen bond — Weak bond between polar molecules.
• Enzyme — Protein catalyst that speeds up reactions.
• Electrolyte — Substance forming ions in solution, conducts electricity.
• Buffer — Substance resisting changes in pH.
• Monosaccharide — Simple sugar.
• Triglyceride — Three fatty acids + glycerol lipid.
• Amino acid — Building block of proteins.
• Nucleotide — Building block of nucleic acids.
• ATP (Adenosine triphosphate) — Main energy molecule in the cell.

Action Items / Next Steps

• Review chemical symbols and major elements in the human body.
• Study pH scale, acid/base definitions, and examples.
• Memorize macromolecule classes, structures, and functions.
• Understand types of chemical bonds and reactions.
• Prepare for questions on the structure and function of water, proteins, and ATP.