Chemistry of Life: Foundations for Anatomy & Physiology

Chemistry of Life

Introduction to Biochemistry

The study of chemistry is fundamental to understanding anatomy and physiology because all biological processes are based on chemical interactions. Biochemistry focuses on the chemical substances and vital processes occurring in living organisms. The basic building blocks of matter are atoms, which combine to form molecules and compounds essential for life.

Levels of Chemical Organization

Atoms and Subatomic Particles

• Atom: The smallest unit of matter, composed of subatomic particles: protons, neutrons, and electrons.

• Proton: Positively charged particle located in the nucleus.

• Neutron: Uncharged particle in the nucleus.

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

• Atomic number: Number of protons in the nucleus.

• Atomic mass: Number of protons and neutrons combined.

Energy Levels (Shells)

• Electrons occupy energy levels around the nucleus.

• Each shell can hold a specific number of electrons (up to 8 in the outermost shell).

• Energy levels increase with distance from the nucleus.

Elements, Molecules, and Compounds

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

• Molecule: Two or more atoms bonded together (e.g., O2).

• Compound: Molecule containing more than one kind of atom (e.g., H2O).

Chemical Bonding

Overview of Chemical Bonds

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

• Ions: Atoms that gain or lose electrons, becoming charged.

• Positive ion (cation): Has lost electrons (e.g., Na+).

• Negative ion (anion): Has gained electrons (e.g., Cl−).

• Ionic bond: Attraction between oppositely charged ions (e.g., NaCl).

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

Covalent Bonds

• Formed when atoms share electrons to fill their outer shells.

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

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

Hydrogen Bonds

• Weak attractions between a hydrogen atom in one molecule and an electronegative atom in another.

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

Inorganic and Organic Chemistry

Classification of Compounds

• Inorganic compounds: Generally do not contain C–C or C–H bonds (e.g., water, salts).

• Organic compounds: Contain C–C and/or C–H bonds; usually larger and more complex (e.g., carbohydrates, proteins).

Water

• Essential inorganic compound; acts as a solvent forming aqueous solutions.

• Participates in chemical reactions such as dehydration synthesis and hydrolysis.

• Involved in energy transfer reactions (e.g., ATP synthesis).

Chemical Equations

• Represent how reactants interact to form products.

• Single arrow ($A + B \rightarrow C$) indicates an irreversible reaction.

• Double arrows ($D + E \rightleftharpoons F$) indicate a reversible reaction.

Acids, Bases, and Salts

• Water dissociates into equal amounts of H+ and OH−.

• Acid: Increases H+ concentration in solution.

• Base (alkaline): Decreases H+ concentration (increases OH−).

• Salt: Compound formed from the neutralization of an acid and a base.

• Buffer: Chemical system that maintains stable pH by absorbing excess acids or bases.

pH Scale

• Measures the concentration of H+ ions in solution.

• pH 7 is neutral; below 7 is acidic, above 7 is basic.

• Human blood pH is slightly alkaline (7.35–7.45).

Organic Compounds

Carbohydrates

• Composed of carbon, hydrogen, and oxygen.

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

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

• Polysaccharides: Complex carbohydrates (e.g., glycogen, starch).

• Primary function: Energy source and storage.

Lipids

• Triglycerides: Glycerol joined to three fatty acids; stores energy.

• Phospholipids: Glycerol, two fatty acids, and a phosphate group; form cell membranes (bilayers).

• Cholesterol: Steroid structure; 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: Include enzymes, hormones, and membrane channels.

• Enzymes: Biological catalysts that speed up chemical reactions (lock-and-key model).

Nucleic Acids

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

• DNA: Contains deoxyribose sugar; bases are adenine (A), thymine (T), cytosine (C), guanine (G); double helix structure; stores genetic information.

• RNA: Contains ribose sugar; bases are adenine (A), uracil (U), cytosine (C), guanine (G); single-stranded; involved in protein synthesis.

Adenosine Triphosphate (ATP)

• Modified nucleotide; main energy carrier in cells.

• Stores and transfers energy for cellular processes.

• ATP hydrolysis releases energy for biological work.

Summary Table: Major Types of Organic Compounds

Example	Components	Functions
Carbohydrate	Monosaccharide units	Energy source, energy storage
Lipid	Glycerol, fatty acids, phosphate	Energy storage, membrane structure, hormones
Protein	Amino acids	Structure, enzymes, regulation
Nucleic Acid	Nucleotides	Genetic information, protein synthesis, energy transfer (ATP)

Summary Table: Important Ions in Body Fluids

Name	Symbol
Sodium (Natrium)	Na+
Chloride	Cl−
Potassium (Kalium)	K+
Calcium	Ca++
Hydrogen	H+
Magnesium	Mg++
Hydroxide	OH−
Phosphate	PO4=
Bicarbonate	HCO3−

Review Questions (Selected)

1. Which of the following are subatomic particles? Answer: Protons, Neutrons, Electrons (All of these)

2. Which chemical bond involves the sharing of electrons to satisfy the outermost energy level? Answer: Covalent

3. Our blood pH typically falls within the range of 7.35 to 7.45. Which of the following describes the pH of the blood? Answer: Slightly alkaline

4. Which of the following is an inorganic molecule? Answer: Water

5. _______ is a sterol lipid that performs several important functions in the body. Answer: Cholesterol

6. Which type of organic molecule is responsible for the structure of enzymes? Answer: Protein

7. Maintaining a relative constancy of the internal environment is defined as: Answer: Homeostasis

8. The events that cause rapid increases in uterine contractions before the birth of a baby are controlled by what feedback loop? Answer: Positive feedback