Chemistry of Life: Foundations for Anatomy & Physiology

Chemistry of Life

Introduction

The chemistry of life forms the foundation for understanding anatomy and physiology. This section explores the structure of atoms, types of chemical bonds, the distinction between organic and inorganic compounds, and the chemical properties of water, acids, bases, and biological macromolecules essential for life.

Levels of Chemical Organization

Atoms

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

• Nucleus: The central core of the atom, containing protons and neutrons.

• Proton: Positively charged particle in the nucleus.

• Neutron: Uncharged particle in the nucleus.

• Atomic number: Number of protons in the nucleus (defines the element).

• Atomic mass: Total number of protons and neutrons in the nucleus.

Energy Levels and Electrons

• Electron: Negatively charged particle found in energy levels (shells) surrounding the nucleus.

• Each energy level can hold up to eight electrons (octet rule).

• Energy levels farther from the nucleus have higher energy.

Elements, Molecules, and Compounds

• Element: Pure substance made of only one kind of atom (e.g., Oxygen, Carbon).

• Molecule: Group of atoms bonded together (e.g., O2).

• Compound: Substance whose molecules contain more than one kind of atom (e.g., H2O).

Chemical Bonding

Overview

• Chemical bonds form to make atoms more stable by filling their outermost energy levels.

• Atoms may share, donate, or borrow electrons to achieve stability.

Ionic Bonds

• Formed when atoms gain or lose electrons, resulting in charged particles called ions.

• Positive ion (cation): Atom that has lost electrons (e.g., Na+).

• Negative ion (anion): Atom that has gained electrons (e.g., Cl-).

• Ionic bonds result from the attraction between oppositely charged ions.

• Electrolyte: Ionic compound that dissociates in water to form ions, conducting electricity.

Covalent Bonds

• Formed when atoms share electrons to fill their outer energy levels.

• Covalent bonds are strong and do not easily dissociate in water.

• All major organic compounds in the body are formed by covalent bonds.

Hydrogen Bonds

• Weak attractions between the positive end of one polar molecule and the negative end of another.

• Do not create new molecules but stabilize structures like water, DNA, and proteins.

Organic vs. Inorganic Compounds

• Organic molecules: Contain carbon-carbon (C–C) and/or carbon-hydrogen (C–H) covalent bonds; generally larger and more complex (e.g., carbohydrates, proteins).

• Inorganic molecules: Do not contain C–C or C–H bonds (e.g., water, salts).

Water: Properties and Functions

• Water is an inorganic compound essential for life.

• Solvent: Dissolves solutes to form aqueous solutions in the body.

• Participates in chemical reactions:

  • Dehydration synthesis: Water is removed to join small molecules into larger ones.

  • Hydrolysis: Water is added to break large molecules into smaller subunits.

• Chemical reactions involve energy transfers, such as the formation of ATP.

Acids, Bases, and Salts

• Water can dissociate into equal amounts of hydrogen ions (H+) and hydroxide ions (OH-).

• Acid: Substance that increases H+ concentration in solution.

• Base (alkaline): Substance that decreases H+ concentration (or increases OH-).

• Salt: Compound formed when acids and bases neutralize each other.

pH Scale

• pH is a mathematical expression of the relative H+ concentration in an aqueous solution.

• $\text{pH} = -\log_{10}[\text{H}^+]$

• pH 7 is neutral; pH > 7 is basic; pH < 7 is acidic.

• Buffers: Chemical systems that absorb excess acids or bases to maintain stable pH.

Organic Molecules

Carbohydrates

• Composed of carbon (C), hydrogen (H), and oxygen (O).

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

• Disaccharides: Double sugars (e.g., sucrose, lactose).

• Polysaccharides: Complex carbohydrates (e.g., glycogen, stored in the body).

Lipids

• Triglycerides: Formed by a glycerol molecule joined to three fatty acids; store energy for later use.

• Phospholipids: Similar to triglycerides but contain a phosphate group; have hydrophilic heads and hydrophobic tails, forming cell membranes.

• Cholesterol: Steroid molecule with multiple rings; stabilizes cell membranes and is a precursor for steroid hormones.

Proteins

• Large molecules made of amino acids linked by peptide bonds.

• Structural proteins: Provide support (e.g., collagen, keratin).

• Functional proteins: Participate in chemical processes (e.g., enzymes, hormones, receptors).

• Enzymes: Biological catalysts that speed up chemical reactions; often described by the lock-and-key model.

Nucleic Acids

• Made of nucleotides (phosphate, sugar, nitrogen base).

• DNA (Deoxyribonucleic Acid): Double helix; contains deoxyribose sugar and bases A, T, C, G; stores genetic code.

• RNA (Ribonucleic Acid): Single-stranded; contains ribose sugar and bases A, U, C, G; acts as a temporary copy of genetic information.

• ATP (Adenosine Triphosphate): Main energy carrier in cells; releases energy when phosphate bonds are broken.

Table: Comparison of Major Biological Molecules

Type	Elements	Monomer	Function	Example
Carbohydrate	C, H, O	Monosaccharide	Energy source, structure	Glucose, glycogen
Lipid	C, H, O (P in phospholipids)	Fatty acid, glycerol	Energy storage, membranes, hormones	Triglyceride, phospholipid, cholesterol
Protein	C, H, O, N, (S)	Amino acid	Structure, enzymes, signaling	Collagen, enzyme, keratin
Nucleic Acid	C, H, O, N, P	Nucleotide	Genetic information, energy transfer	DNA, RNA, ATP

Summary

• The chemistry of life underpins all biological structure and function, from the atomic level to complex macromolecules.

• Understanding chemical bonds, water chemistry, acids, bases, and the structure of organic molecules is essential for studying anatomy and physiology.