The Chemistry of Life

Introduction

Chemistry forms the foundation of human anatomy and physiology. All structures and functions of the body are based on chemical principles, from the composition of bones to the transmission of nerve impulses. Understanding the chemical level of organization is essential for comprehending higher levels of biological complexity.

Atoms and Elements

Basic Definitions

• Matter: Anything that has mass and occupies space.

• Chemistry: The study of matter and its interactions.

• Atom: The smallest unit of matter that retains the properties of an element.

• Element: A substance composed of one type of atom; cannot be broken down by chemical means.

Atomic Structure

• Protons: Positively charged particles in the atomic nucleus.

• Neutrons: Uncharged particles, slightly larger than protons, also in the nucleus.

• Electrons: Negatively charged particles that orbit the nucleus in electron shells.

• Atoms are electrically neutral when the number of protons equals the number of electrons.

• Electron shells: 1st shell holds 2 electrons, 2nd holds 8, 3rd holds up to 18 (satisfied with 8).

Elements in the Human Body

• Elements are defined by their atomic number (number of protons).

• The Periodic Table organizes elements by atomic number and recurring properties.

• Four major elements make up 96% of body mass: Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N).

• Mineral elements (e.g., Na, K, Ca, Cl, Mg, P, S) and trace elements (e.g., Fe, Cu, I, Zn) are also essential.

Isotopes and Radioactivity

• Isotopes: Atoms of the same element with different numbers of neutrons (different mass numbers).

• Radioisotopes: Unstable isotopes that emit radiation; used in nuclear medicine (e.g., cancer therapy, thyroid treatment).

Matter Combined: Mixtures and Chemical Bonds

Mixtures

• Mixture: Physical combination of two or more substances; components retain their properties and can be separated physically.

• Molecule: Chemical combination of two or more atoms; properties differ from constituent atoms; separation requires chemical means.

Types of Mixtures

• Suspensions: Large particles, visible, settle out (e.g., blood).

• Colloids: Small particles, not visible, do not settle (e.g., milk).

• Solutions: Solute dissolves in solvent, appears clear (e.g., glucose in water).

Chemical Bonds

• Chemical bond: Attractive force holding atoms together.

• Valence electrons: Electrons in the outermost shell; involved in bonding.

• Octet Rule: Atoms are most stable with 8 electrons in their valence shell (2 for very small atoms).

Ionic Bonds

• Formed by transfer of electrons from a metal to a nonmetal.

• Cation: Positively charged ion (lost electrons).

• Anion: Negatively charged ion (gained electrons).

• Resulting compounds are called salts.

Covalent Bonds

• Formed by sharing electrons between nonmetals; strongest type of bond.

• Single, double, or triple bonds possible depending on number of shared electron pairs.

• Nonpolar covalent bond: Electrons shared equally (e.g., O2, H2).

• Polar covalent bond: Electrons shared unequally, creating partial charges (e.g., H2O).

Hydrogen Bonds

• Weak attractions between partially positive hydrogen and partially negative atoms in polar molecules.

• Responsible for properties like surface tension in water.

Chemical Notation and Reactions

Chemical Equations

• Reactants: Substances that undergo change (left side).

• Products: Substances formed (right side).

• Reversible reactions: Indicated by double arrows; can proceed in both directions.

• Irreversible reactions: Indicated by a single arrow; proceed in one direction.

Energy in Chemical Reactions

• Energy: Capacity to do work; can be potential (stored) or kinetic (in motion).

• Chemical energy: Stored in bonds; fuels cellular processes.

• Endergonic reactions: Require energy input; products have more energy than reactants.

• Exergonic reactions: Release energy; products have less energy than reactants.

Types of Chemical Reactions in the Body

• Catabolic reactions: Break down large molecules; generally exergonic.

• Exchange reactions: Atoms or electrons are exchanged between reactants (includes redox reactions).

• Anabolic reactions: Build new molecules; generally endergonic.

Enzymes and Reaction Rates

• Activation energy: Minimum energy required for a reaction to occur.

• Catalysts: Lower activation energy, increasing reaction rate; biological catalysts are called enzymes.

• Enzymes are highly specific, not consumed in reactions, and dramatically speed up reactions.

Enzyme Deficiencies

• Tay-Sachs Disease: Deficiency of hexosaminidase; leads to fatal accumulation of lipids in brain cells.

• SCIDS: Deficiency of adenosine deaminase; results in severe immune deficiency.

• Phenylketonuria: Deficiency of phenylalanine hydroxylase; can cause intellectual disability if untreated.

Inorganic Compounds: Water, Acids, Bases, and Salts

Water

• Makes up 50–65% of body mass; vital for life.

• Absorbs and carries heat, cushions and protects, acts as a lubricant, and is the primary solvent in the body.

• Hydrophilic substances dissolve in water; hydrophobic substances do not.

Acids and Bases

• Acids: Proton (H+) donors; increase H+ concentration in water.

• Bases: Proton acceptors; decrease H+ concentration in water.

• pH scale: Measures hydrogen ion concentration; 7 is neutral, below 7 is acidic, above 7 is basic.

• Buffers: Chemical systems that resist changes in pH; essential for maintaining homeostasis (e.g., carbonic acid–bicarbonate buffer in blood).

Salts and Electrolytes

• Salts: Compounds formed from the reaction of an acid and a base; dissociate into ions in water.

• Electrolytes: Ions in solution that conduct electricity; essential for nerve and muscle function.

Organic Compounds

Hydrocarbons

• Organic compounds containing only carbon and hydrogen; form chains and rings that serve as the backbone for all organic molecules.

Monomers and Polymers

• Four main organic compounds: Carbohydrates, Lipids, Proteins, Nucleic Acids.

• Monomers: Single subunits; Polymers: Chains of monomers.

• Dehydration synthesis: Joins monomers by removing water.

• Hydrolysis: Breaks polymers by adding water.

Carbohydrates

• Composed of C, H, O (1:2:1 ratio); polar and hydrophilic.

• Primary function: fuel; also structural roles.

• Monosaccharides: Simple sugars (e.g., glucose, fructose, galactose).

• Disaccharides: Two monosaccharides joined (e.g., sucrose, lactose).

• Polysaccharides: Long chains (e.g., glycogen in animals, starch in plants).

Lipids

• Composed mainly of C, H, and some O; nonpolar and hydrophobic.

• Functions: energy storage, cell membrane structure, hormone production.

• Fatty acids: Saturated (no double bonds), monounsaturated (one double bond), polyunsaturated (multiple double bonds).

• Triglycerides: Three fatty acids + glycerol; main storage form of fat.

• Phospholipids: Glycerol, two fatty acids, phosphate group; amphiphilic; main component of cell membranes.

• Steroids: Four-ring structure; includes cholesterol, bile acids, and hormones.

Proteins

• Composed of C, H, O, N, and sometimes S; may be polar or nonpolar.

• Functions: structure, enzymes, defense, communication, movement, fuel.

• Amino acids: 21 types; monomers of proteins.

• Peptide bonds: Link amino acids via dehydration synthesis.

• Protein structure: Primary (sequence), secondary (alpha helix, beta sheet), tertiary (3D folding), quaternary (multiple polypeptides).

• Denaturation: Loss of structure and function due to heat, pH, or chemicals.

Nucleotides and Nucleic Acids

• Composed of C, H, O, N, P; include DNA and RNA.

• Nucleotides: Monomers with a nitrogenous base, five-carbon sugar, and phosphate group.

• ATP: Main energy currency of the cell; formed from ADP and phosphate.

• DNA: Double helix; stores genetic code; bases: A, T, G, C.

• RNA: Single strand; involved in protein synthesis; bases: A, U, G, C.

Additional info: This summary covers all major concepts from Chapter 2, providing foundational chemistry knowledge essential for understanding anatomy and physiology. Students are encouraged to use these notes alongside practice questions and concept maps for effective exam preparation.